| Message ID | 20190822134551.18924-1-iii@linux.ibm.com |
|---|---|
| Headers | show |
| Series | S/390: Use signaling FP comparison instructions | expand |
> Am 22.08.2019 um 15:45 schrieb Ilya Leoshkevich <iii@linux.ibm.com>: > > Bootstrap and regtest running on x86_64-redhat-linux and > s390x-redhat-linux. > > This patch series adds signaling FP comparison support (both scalar and > vector) to s390 backend. I'm running into a problem on ppc64 with this patch, and it would be great if someone could help me figure out the best way to resolve it. vector36.C test is failing because gimplifier produces the following _5 = _4 > { 2.0e+0, 2.0e+0, 2.0e+0, 2.0e+0 }; _6 = VEC_COND_EXPR <_5, { -1, -1, -1, -1 }, { 0, 0, 0, 0 }>; from VEC_COND_EXPR < (*b > { 2.0e+0, 2.0e+0, 2.0e+0, 2.0e+0 }) , { -1, -1, -1, -1 } , { 0, 0, 0, 0 } > Since the comparison tree code is now hidden behind a temporary, my code does not have anything to pass to the backend. The reason for creating a temporary is that the comparison can trap, and so the following check in gimplify_expr fails: if (gimple_seq_empty_p (internal_post) && (*gimple_test_f) (*expr_p)) goto out; gimple_test_f is is_gimple_condexpr, and it eventually calls operation_could_trap_p (GT). My current solution is to simply state that backend does not support SSA_NAME in vector comparisons, however, I don't like it, since it may cause performance regressions due to having to fall back to scalar comparisons. I was thinking about two other possible solutions: 1. Change the gimplifier to allow trapping vector comparisons. That's a bit complicated, because tree_could_throw_p checks not only for floating point traps, but also e.g. for array index out of bounds traps. So I would have to create a tree_could_throw_p version which disregards specific kinds of traps. 2. Change expand_vector_condition to follow SSA_NAME_DEF_STMT and use its tree_code instead of SSA_NAME. The potential problem I see with this is that there appears to be no guarantee that _5 will be inlined into _6 at a later point. So if we say that we don't need to fall back to scalar comparisons based on availability of vector > instruction and inlining does not happen, then what's actually will be required is vector selection (vsel on S/390), which might not be available in general case. What would be a better way to proceed here?
On Thu, Aug 29, 2019 at 5:39 PM Ilya Leoshkevich <iii@linux.ibm.com> wrote: > > > Am 22.08.2019 um 15:45 schrieb Ilya Leoshkevich <iii@linux.ibm.com>: > > > > Bootstrap and regtest running on x86_64-redhat-linux and > > s390x-redhat-linux. > > > > This patch series adds signaling FP comparison support (both scalar and > > vector) to s390 backend. > > I'm running into a problem on ppc64 with this patch, and it would be > great if someone could help me figure out the best way to resolve it. > > vector36.C test is failing because gimplifier produces the following > > _5 = _4 > { 2.0e+0, 2.0e+0, 2.0e+0, 2.0e+0 }; > _6 = VEC_COND_EXPR <_5, { -1, -1, -1, -1 }, { 0, 0, 0, 0 }>; > > from > > VEC_COND_EXPR < (*b > { 2.0e+0, 2.0e+0, 2.0e+0, 2.0e+0 }) , > { -1, -1, -1, -1 } , > { 0, 0, 0, 0 } > > > Since the comparison tree code is now hidden behind a temporary, my code > does not have anything to pass to the backend. The reason for creating > a temporary is that the comparison can trap, and so the following check > in gimplify_expr fails: > > if (gimple_seq_empty_p (internal_post) && (*gimple_test_f) (*expr_p)) > goto out; > > gimple_test_f is is_gimple_condexpr, and it eventually calls > operation_could_trap_p (GT). > > My current solution is to simply state that backend does not support > SSA_NAME in vector comparisons, however, I don't like it, since it may > cause performance regressions due to having to fall back to scalar > comparisons. > > I was thinking about two other possible solutions: > > 1. Change the gimplifier to allow trapping vector comparisons. That's > a bit complicated, because tree_could_throw_p checks not only for > floating point traps, but also e.g. for array index out of bounds > traps. So I would have to create a tree_could_throw_p version which > disregards specific kinds of traps. > > 2. Change expand_vector_condition to follow SSA_NAME_DEF_STMT and use > its tree_code instead of SSA_NAME. The potential problem I see with > this is that there appears to be no guarantee that _5 will be inlined > into _6 at a later point. So if we say that we don't need to fall > back to scalar comparisons based on availability of vector > > instruction and inlining does not happen, then what's actually will > be required is vector selection (vsel on S/390), which might not be > available in general case. > > What would be a better way to proceed here? On GIMPLE there isn't a good reason to split out trapping comparisons from [VEC_]COND_EXPR - the gimplifier does this for GIMPLE_CONDs where it is important because we'd have no way to represent EH info when not done. It might be a bit awkward to preserve EH across RTL expansion though in case the [VEC_]COND_EXPR are not expanded as a single pattern, but I'm not sure. To go this route you'd have to split the is_gimple_condexpr check I guess and eventually users turning [VEC_]COND_EXPR into conditional code (do we have any?) have to be extra careful then. Richard. >
On Fri, Aug 30, 2019 at 9:12 AM Richard Biener <richard.guenther@gmail.com> wrote: > > On Thu, Aug 29, 2019 at 5:39 PM Ilya Leoshkevich <iii@linux.ibm.com> wrote: > > > > > Am 22.08.2019 um 15:45 schrieb Ilya Leoshkevich <iii@linux.ibm.com>: > > > > > > Bootstrap and regtest running on x86_64-redhat-linux and > > > s390x-redhat-linux. > > > > > > This patch series adds signaling FP comparison support (both scalar and > > > vector) to s390 backend. > > > > I'm running into a problem on ppc64 with this patch, and it would be > > great if someone could help me figure out the best way to resolve it. > > > > vector36.C test is failing because gimplifier produces the following > > > > _5 = _4 > { 2.0e+0, 2.0e+0, 2.0e+0, 2.0e+0 }; > > _6 = VEC_COND_EXPR <_5, { -1, -1, -1, -1 }, { 0, 0, 0, 0 }>; > > > > from > > > > VEC_COND_EXPR < (*b > { 2.0e+0, 2.0e+0, 2.0e+0, 2.0e+0 }) , > > { -1, -1, -1, -1 } , > > { 0, 0, 0, 0 } > > > > > Since the comparison tree code is now hidden behind a temporary, my code > > does not have anything to pass to the backend. The reason for creating > > a temporary is that the comparison can trap, and so the following check > > in gimplify_expr fails: > > > > if (gimple_seq_empty_p (internal_post) && (*gimple_test_f) (*expr_p)) > > goto out; > > > > gimple_test_f is is_gimple_condexpr, and it eventually calls > > operation_could_trap_p (GT). > > > > My current solution is to simply state that backend does not support > > SSA_NAME in vector comparisons, however, I don't like it, since it may > > cause performance regressions due to having to fall back to scalar > > comparisons. > > > > I was thinking about two other possible solutions: > > > > 1. Change the gimplifier to allow trapping vector comparisons. That's > > a bit complicated, because tree_could_throw_p checks not only for > > floating point traps, but also e.g. for array index out of bounds > > traps. So I would have to create a tree_could_throw_p version which > > disregards specific kinds of traps. > > > > 2. Change expand_vector_condition to follow SSA_NAME_DEF_STMT and use > > its tree_code instead of SSA_NAME. The potential problem I see with > > this is that there appears to be no guarantee that _5 will be inlined > > into _6 at a later point. So if we say that we don't need to fall > > back to scalar comparisons based on availability of vector > > > instruction and inlining does not happen, then what's actually will > > be required is vector selection (vsel on S/390), which might not be > > available in general case. > > > > What would be a better way to proceed here? > > On GIMPLE there isn't a good reason to split out trapping comparisons > from [VEC_]COND_EXPR - the gimplifier does this for GIMPLE_CONDs > where it is important because we'd have no way to represent EH info > when not done. It might be a bit awkward to preserve EH across RTL > expansion though in case the [VEC_]COND_EXPR are not expanded > as a single pattern, but I'm not sure. > > To go this route you'd have to split the is_gimple_condexpr check > I guess and eventually users turning [VEC_]COND_EXPR into conditional > code (do we have any?) have to be extra careful then. Oh, btw - the fact that we have an expression embedded in [VEC_]COND_EXPR is something that bothers me for quite some time already and it makes things like VN awkward and GIMPLE fincky. We've discussed alternatives to dead with the simplest being moving the comparison out to a separate stmt and others like having four operand [VEC_]COND_{EQ,NE,...}_EXPR codes or simply treating {EQ,NE,...}_EXPR as quarternary on GIMPLE with either optional 3rd and 4th operand (defaulting to boolean_true/false_node) or always explicit ones (and thus dropping [VEC_]COND_EXPR). What does LLVM do here? Richard. > Richard. > > >
On Fri, Aug 30, 2019 at 09:12:11AM +0200, Richard Biener wrote: > On GIMPLE there isn't a good reason to split out trapping comparisons > from [VEC_]COND_EXPR - the gimplifier does this for GIMPLE_CONDs > where it is important because we'd have no way to represent EH info > when not done. It might be a bit awkward to preserve EH across RTL > expansion though in case the [VEC_]COND_EXPR are not expanded > as a single pattern, but I'm not sure. The *language* specifies which comparisons trap on unordered and which do not. (Hopefully it is similar for all or this is going to be a huge mess :-) ) So Gimple needs to at least keep track of this. There also are various optimisations that can be done -- two signaling comparisons with the same arguments can be folded to just one, for example -- so it seems to me you want to represent this in Gimple, never mind if you do EH for them or just a magical trap or whatever. Segher
On Fri, Aug 30, 2019 at 12:06 PM Segher Boessenkool <segher@kernel.crashing.org> wrote: > > On Fri, Aug 30, 2019 at 09:12:11AM +0200, Richard Biener wrote: > > On GIMPLE there isn't a good reason to split out trapping comparisons > > from [VEC_]COND_EXPR - the gimplifier does this for GIMPLE_CONDs > > where it is important because we'd have no way to represent EH info > > when not done. It might be a bit awkward to preserve EH across RTL > > expansion though in case the [VEC_]COND_EXPR are not expanded > > as a single pattern, but I'm not sure. > > The *language* specifies which comparisons trap on unordered and which > do not. (Hopefully it is similar for all or this is going to be a huge > mess :-) ) So Gimple needs to at least keep track of this. There also > are various optimisations that can be done -- two signaling comparisons > with the same arguments can be folded to just one, for example -- so it > seems to me you want to represent this in Gimple, never mind if you do > EH for them or just a magical trap or whatever. The issue with GIMPLE_CONDs is that we can't have EH edges out of blocks ending in them so to represent the compare-and-jump single GIMPLE insn raising exceptions we need to split the actually trapping compare away. For [VEC_]COND_EXPR we'd need to say the whole expression can throw/trap if the embedded comparison can. On GIMPLE this is enough precision but we of course have to handle it that way then. Currently operation_could_trap* do not consider [VEC_]COND_EXPR trapping nor does tree_could_trap_p. stmt_could_throw_1_p looks fine by means of falling back to checking individual operands and then running into the embedded comparison. But we do have operation_could_trap* callers which would need to be adjusted on the GIMPLE side. Richard. > > Segher
> Am 30.08.2019 um 09:16 schrieb Richard Biener <richard.guenther@gmail.com>: > > On Fri, Aug 30, 2019 at 9:12 AM Richard Biener > <richard.guenther@gmail.com> wrote: >> >> On Thu, Aug 29, 2019 at 5:39 PM Ilya Leoshkevich <iii@linux.ibm.com> wrote: >>> >>>> Am 22.08.2019 um 15:45 schrieb Ilya Leoshkevich <iii@linux.ibm.com>: >>>> >>>> Bootstrap and regtest running on x86_64-redhat-linux and >>>> s390x-redhat-linux. >>>> >>>> This patch series adds signaling FP comparison support (both scalar and >>>> vector) to s390 backend. >>> >>> I'm running into a problem on ppc64 with this patch, and it would be >>> great if someone could help me figure out the best way to resolve it. >>> >>> vector36.C test is failing because gimplifier produces the following >>> >>> _5 = _4 > { 2.0e+0, 2.0e+0, 2.0e+0, 2.0e+0 }; >>> _6 = VEC_COND_EXPR <_5, { -1, -1, -1, -1 }, { 0, 0, 0, 0 }>; >>> >>> from >>> >>> VEC_COND_EXPR < (*b > { 2.0e+0, 2.0e+0, 2.0e+0, 2.0e+0 }) , >>> { -1, -1, -1, -1 } , >>> { 0, 0, 0, 0 } > >>> >>> Since the comparison tree code is now hidden behind a temporary, my code >>> does not have anything to pass to the backend. The reason for creating >>> a temporary is that the comparison can trap, and so the following check >>> in gimplify_expr fails: >>> >>> if (gimple_seq_empty_p (internal_post) && (*gimple_test_f) (*expr_p)) >>> goto out; >>> >>> gimple_test_f is is_gimple_condexpr, and it eventually calls >>> operation_could_trap_p (GT). >>> >>> My current solution is to simply state that backend does not support >>> SSA_NAME in vector comparisons, however, I don't like it, since it may >>> cause performance regressions due to having to fall back to scalar >>> comparisons. >>> >>> I was thinking about two other possible solutions: >>> >>> 1. Change the gimplifier to allow trapping vector comparisons. That's >>> a bit complicated, because tree_could_throw_p checks not only for >>> floating point traps, but also e.g. for array index out of bounds >>> traps. So I would have to create a tree_could_throw_p version which >>> disregards specific kinds of traps. >>> >>> 2. Change expand_vector_condition to follow SSA_NAME_DEF_STMT and use >>> its tree_code instead of SSA_NAME. The potential problem I see with >>> this is that there appears to be no guarantee that _5 will be inlined >>> into _6 at a later point. So if we say that we don't need to fall >>> back to scalar comparisons based on availability of vector > >>> instruction and inlining does not happen, then what's actually will >>> be required is vector selection (vsel on S/390), which might not be >>> available in general case. >>> >>> What would be a better way to proceed here? >> >> On GIMPLE there isn't a good reason to split out trapping comparisons >> from [VEC_]COND_EXPR - the gimplifier does this for GIMPLE_CONDs >> where it is important because we'd have no way to represent EH info >> when not done. It might be a bit awkward to preserve EH across RTL >> expansion though in case the [VEC_]COND_EXPR are not expanded >> as a single pattern, but I'm not sure. >> >> To go this route you'd have to split the is_gimple_condexpr check >> I guess and eventually users turning [VEC_]COND_EXPR into conditional >> code (do we have any?) have to be extra careful then. > > Oh, btw - the fact that we have an expression embedded in [VEC_]COND_EXPR > is something that bothers me for quite some time already and it makes > things like VN awkward and GIMPLE fincky. We've discussed alternatives > to dead with the simplest being moving the comparison out to a separate > stmt and others like having four operand [VEC_]COND_{EQ,NE,...}_EXPR > codes or simply treating {EQ,NE,...}_EXPR as quarternary on GIMPLE > with either optional 3rd and 4th operand (defaulting to boolean_true/false_node) > or always explicit ones (and thus dropping [VEC_]COND_EXPR). > > What does LLVM do here? For void f(long long * restrict w, double * restrict x, double * restrict y, int n) { for (int i = 0; i < n; i++) w[i] = x[i] == y[i] ? x[i] : y[i]; } LLVM does %26 = fcmp oeq <2 x double> %21, %25 %27 = extractelement <2 x i1> %26, i32 0 %28 = select <2 x i1> %26, <2 x double> %21, <2 x double> %25 So they have separate operations for comparisons and ternary operator (fcmp + select).
> Am 30.08.2019 um 09:12 schrieb Richard Biener <richard.guenther@gmail.com>: > > On Thu, Aug 29, 2019 at 5:39 PM Ilya Leoshkevich <iii@linux.ibm.com> wrote: >> >>> Am 22.08.2019 um 15:45 schrieb Ilya Leoshkevich <iii@linux.ibm.com>: >>> >>> Bootstrap and regtest running on x86_64-redhat-linux and >>> s390x-redhat-linux. >>> >>> This patch series adds signaling FP comparison support (both scalar and >>> vector) to s390 backend. >> >> I'm running into a problem on ppc64 with this patch, and it would be >> great if someone could help me figure out the best way to resolve it. >> >> vector36.C test is failing because gimplifier produces the following >> >> _5 = _4 > { 2.0e+0, 2.0e+0, 2.0e+0, 2.0e+0 }; >> _6 = VEC_COND_EXPR <_5, { -1, -1, -1, -1 }, { 0, 0, 0, 0 }>; >> >> from >> >> VEC_COND_EXPR < (*b > { 2.0e+0, 2.0e+0, 2.0e+0, 2.0e+0 }) , >> { -1, -1, -1, -1 } , >> { 0, 0, 0, 0 } > >> >> Since the comparison tree code is now hidden behind a temporary, my code >> does not have anything to pass to the backend. The reason for creating >> a temporary is that the comparison can trap, and so the following check >> in gimplify_expr fails: >> >> if (gimple_seq_empty_p (internal_post) && (*gimple_test_f) (*expr_p)) >> goto out; >> >> gimple_test_f is is_gimple_condexpr, and it eventually calls >> operation_could_trap_p (GT). >> >> My current solution is to simply state that backend does not support >> SSA_NAME in vector comparisons, however, I don't like it, since it may >> cause performance regressions due to having to fall back to scalar >> comparisons. >> >> I was thinking about two other possible solutions: >> >> 1. Change the gimplifier to allow trapping vector comparisons. That's >> a bit complicated, because tree_could_throw_p checks not only for >> floating point traps, but also e.g. for array index out of bounds >> traps. So I would have to create a tree_could_throw_p version which >> disregards specific kinds of traps. >> >> 2. Change expand_vector_condition to follow SSA_NAME_DEF_STMT and use >> its tree_code instead of SSA_NAME. The potential problem I see with >> this is that there appears to be no guarantee that _5 will be inlined >> into _6 at a later point. So if we say that we don't need to fall >> back to scalar comparisons based on availability of vector > >> instruction and inlining does not happen, then what's actually will >> be required is vector selection (vsel on S/390), which might not be >> available in general case. >> >> What would be a better way to proceed here? > > On GIMPLE there isn't a good reason to split out trapping comparisons > from [VEC_]COND_EXPR - the gimplifier does this for GIMPLE_CONDs > where it is important because we'd have no way to represent EH info > when not done. It might be a bit awkward to preserve EH across RTL > expansion though in case the [VEC_]COND_EXPR are not expanded > as a single pattern, but I'm not sure. Ok, so I'm testing the following now - for the problematic test that helped: diff --git a/gcc/gimple-expr.c b/gcc/gimple-expr.c index b0c9f9b671a..940aa394769 100644 --- a/gcc/gimple-expr.c +++ b/gcc/gimple-expr.c @@ -602,17 +602,33 @@ is_gimple_lvalue (tree t) || TREE_CODE (t) == BIT_FIELD_REF); } -/* Return true if T is a GIMPLE condition. */ +/* Helper for is_gimple_condexpr and is_possibly_trapping_gimple_condexpr. */ -bool -is_gimple_condexpr (tree t) +static bool +is_gimple_condexpr_1 (tree t, bool allow_traps) { return (is_gimple_val (t) || (COMPARISON_CLASS_P (t) - && !tree_could_throw_p (t) + && (allow_traps || !tree_could_throw_p (t)) && is_gimple_val (TREE_OPERAND (t, 0)) && is_gimple_val (TREE_OPERAND (t, 1)))); } +/* Return true if T is a GIMPLE condition. */ + +bool +is_gimple_condexpr (tree t) +{ + return is_gimple_condexpr_1 (t, false); +} + +/* Like is_gimple_condexpr, but allow the T to trap. */ + +bool +is_possibly_trapping_gimple_condexpr (tree t) +{ + return is_gimple_condexpr_1 (t, true); +} + /* Return true if T is a gimple address. */ bool diff --git a/gcc/gimple-expr.h b/gcc/gimple-expr.h index 1ad1432bd17..20546ca5b99 100644 --- a/gcc/gimple-expr.h +++ b/gcc/gimple-expr.h @@ -41,6 +41,7 @@ extern void gimple_cond_get_ops_from_tree (tree, enum tree_code *, tree *, tree *); extern bool is_gimple_lvalue (tree); extern bool is_gimple_condexpr (tree); +extern bool is_possibly_trapping_gimple_condexpr (tree); extern bool is_gimple_address (const_tree); extern bool is_gimple_invariant_address (const_tree); extern bool is_gimple_ip_invariant_address (const_tree); diff --git a/gcc/gimplify.c b/gcc/gimplify.c index daa0b71c191..4e6256390c0 100644 --- a/gcc/gimplify.c +++ b/gcc/gimplify.c @@ -12973,6 +12973,7 @@ gimplify_expr (tree *expr_p, gimple_seq *pre_p, gimple_seq *post_p, else if (gimple_test_f == is_gimple_val || gimple_test_f == is_gimple_call_addr || gimple_test_f == is_gimple_condexpr + || gimple_test_f == is_possibly_trapping_gimple_condexpr || gimple_test_f == is_gimple_mem_rhs || gimple_test_f == is_gimple_mem_rhs_or_call || gimple_test_f == is_gimple_reg_rhs @@ -13814,7 +13815,7 @@ gimplify_expr (tree *expr_p, gimple_seq *pre_p, gimple_seq *post_p, enum gimplify_status r0, r1, r2; r0 = gimplify_expr (&TREE_OPERAND (*expr_p, 0), pre_p, - post_p, is_gimple_condexpr, fb_rvalue); + post_p, is_possibly_trapping_gimple_condexpr, fb_rvalue); r1 = gimplify_expr (&TREE_OPERAND (*expr_p, 1), pre_p, post_p, is_gimple_val, fb_rvalue); r2 = gimplify_expr (&TREE_OPERAND (*expr_p, 2), pre_p, diff --git a/gcc/tree-cfg.c b/gcc/tree-cfg.c index b75fdb2e63f..175b858f56b 100644 --- a/gcc/tree-cfg.c +++ b/gcc/tree-cfg.c @@ -4121,8 +4121,11 @@ verify_gimple_assign_ternary (gassign *stmt) return true; } - if (((rhs_code == VEC_COND_EXPR || rhs_code == COND_EXPR) - ? !is_gimple_condexpr (rhs1) : !is_gimple_val (rhs1)) + if ((rhs_code == VEC_COND_EXPR + ? !is_possibly_trapping_gimple_condexpr (rhs1) + : (rhs_code == COND_EXPR + ? !is_gimple_condexpr (rhs1) + : !is_gimple_val (rhs1))) || !is_gimple_val (rhs2) || !is_gimple_val (rhs3)) { > > To go this route you'd have to split the is_gimple_condexpr check > I guess and eventually users turning [VEC_]COND_EXPR into conditional > code (do we have any?) have to be extra careful then. > We have expand_vector_condition, which turns VEC_COND_EXPR into COND_EXPR - but this should be harmless, right? I could not find anything else.
> Am 30.08.2019 um 16:40 schrieb Ilya Leoshkevich <iii@linux.ibm.com>: > >> Am 30.08.2019 um 09:12 schrieb Richard Biener <richard.guenther@gmail.com>: >> >> On Thu, Aug 29, 2019 at 5:39 PM Ilya Leoshkevich <iii@linux.ibm.com> wrote: >>> >>>> Am 22.08.2019 um 15:45 schrieb Ilya Leoshkevich <iii@linux.ibm.com>: >>>> >>>> Bootstrap and regtest running on x86_64-redhat-linux and >>>> s390x-redhat-linux. >>>> >>>> This patch series adds signaling FP comparison support (both scalar and >>>> vector) to s390 backend. >>> >>> I'm running into a problem on ppc64 with this patch, and it would be >>> great if someone could help me figure out the best way to resolve it. >>> >>> vector36.C test is failing because gimplifier produces the following >>> >>> _5 = _4 > { 2.0e+0, 2.0e+0, 2.0e+0, 2.0e+0 }; >>> _6 = VEC_COND_EXPR <_5, { -1, -1, -1, -1 }, { 0, 0, 0, 0 }>; >>> >>> from >>> >>> VEC_COND_EXPR < (*b > { 2.0e+0, 2.0e+0, 2.0e+0, 2.0e+0 }) , >>> { -1, -1, -1, -1 } , >>> { 0, 0, 0, 0 } > >>> >>> Since the comparison tree code is now hidden behind a temporary, my code >>> does not have anything to pass to the backend. The reason for creating >>> a temporary is that the comparison can trap, and so the following check >>> in gimplify_expr fails: >>> >>> if (gimple_seq_empty_p (internal_post) && (*gimple_test_f) (*expr_p)) >>> goto out; >>> >>> gimple_test_f is is_gimple_condexpr, and it eventually calls >>> operation_could_trap_p (GT). >>> >>> My current solution is to simply state that backend does not support >>> SSA_NAME in vector comparisons, however, I don't like it, since it may >>> cause performance regressions due to having to fall back to scalar >>> comparisons. >>> >>> I was thinking about two other possible solutions: >>> >>> 1. Change the gimplifier to allow trapping vector comparisons. That's >>> a bit complicated, because tree_could_throw_p checks not only for >>> floating point traps, but also e.g. for array index out of bounds >>> traps. So I would have to create a tree_could_throw_p version which >>> disregards specific kinds of traps. >>> >>> 2. Change expand_vector_condition to follow SSA_NAME_DEF_STMT and use >>> its tree_code instead of SSA_NAME. The potential problem I see with >>> this is that there appears to be no guarantee that _5 will be inlined >>> into _6 at a later point. So if we say that we don't need to fall >>> back to scalar comparisons based on availability of vector > >>> instruction and inlining does not happen, then what's actually will >>> be required is vector selection (vsel on S/390), which might not be >>> available in general case. >>> >>> What would be a better way to proceed here? >> >> On GIMPLE there isn't a good reason to split out trapping comparisons >> from [VEC_]COND_EXPR - the gimplifier does this for GIMPLE_CONDs >> where it is important because we'd have no way to represent EH info >> when not done. It might be a bit awkward to preserve EH across RTL >> expansion though in case the [VEC_]COND_EXPR are not expanded >> as a single pattern, but I'm not sure. > > Ok, so I'm testing the following now - for the problematic test that > helped: > > diff --git a/gcc/gimple-expr.c b/gcc/gimple-expr.c > index b0c9f9b671a..940aa394769 100644 > --- a/gcc/gimple-expr.c > +++ b/gcc/gimple-expr.c > @@ -602,17 +602,33 @@ is_gimple_lvalue (tree t) > || TREE_CODE (t) == BIT_FIELD_REF); > } > > -/* Return true if T is a GIMPLE condition. */ > +/* Helper for is_gimple_condexpr and is_possibly_trapping_gimple_condexpr. */ > > -bool > -is_gimple_condexpr (tree t) > +static bool > +is_gimple_condexpr_1 (tree t, bool allow_traps) > { > return (is_gimple_val (t) || (COMPARISON_CLASS_P (t) > - && !tree_could_throw_p (t) > + && (allow_traps || !tree_could_throw_p (t)) > && is_gimple_val (TREE_OPERAND (t, 0)) > && is_gimple_val (TREE_OPERAND (t, 1)))); > } > > +/* Return true if T is a GIMPLE condition. */ > + > +bool > +is_gimple_condexpr (tree t) > +{ > + return is_gimple_condexpr_1 (t, false); > +} > + > +/* Like is_gimple_condexpr, but allow the T to trap. */ > + > +bool > +is_possibly_trapping_gimple_condexpr (tree t) > +{ > + return is_gimple_condexpr_1 (t, true); > +} > + > /* Return true if T is a gimple address. */ > > bool > diff --git a/gcc/gimple-expr.h b/gcc/gimple-expr.h > index 1ad1432bd17..20546ca5b99 100644 > --- a/gcc/gimple-expr.h > +++ b/gcc/gimple-expr.h > @@ -41,6 +41,7 @@ extern void gimple_cond_get_ops_from_tree (tree, enum tree_code *, tree *, > tree *); > extern bool is_gimple_lvalue (tree); > extern bool is_gimple_condexpr (tree); > +extern bool is_possibly_trapping_gimple_condexpr (tree); > extern bool is_gimple_address (const_tree); > extern bool is_gimple_invariant_address (const_tree); > extern bool is_gimple_ip_invariant_address (const_tree); > diff --git a/gcc/gimplify.c b/gcc/gimplify.c > index daa0b71c191..4e6256390c0 100644 > --- a/gcc/gimplify.c > +++ b/gcc/gimplify.c > @@ -12973,6 +12973,7 @@ gimplify_expr (tree *expr_p, gimple_seq *pre_p, gimple_seq *post_p, > else if (gimple_test_f == is_gimple_val > || gimple_test_f == is_gimple_call_addr > || gimple_test_f == is_gimple_condexpr > + || gimple_test_f == is_possibly_trapping_gimple_condexpr > || gimple_test_f == is_gimple_mem_rhs > || gimple_test_f == is_gimple_mem_rhs_or_call > || gimple_test_f == is_gimple_reg_rhs > @@ -13814,7 +13815,7 @@ gimplify_expr (tree *expr_p, gimple_seq *pre_p, gimple_seq *post_p, > enum gimplify_status r0, r1, r2; > > r0 = gimplify_expr (&TREE_OPERAND (*expr_p, 0), pre_p, > - post_p, is_gimple_condexpr, fb_rvalue); > + post_p, is_possibly_trapping_gimple_condexpr, fb_rvalue); > r1 = gimplify_expr (&TREE_OPERAND (*expr_p, 1), pre_p, > post_p, is_gimple_val, fb_rvalue); > r2 = gimplify_expr (&TREE_OPERAND (*expr_p, 2), pre_p, > diff --git a/gcc/tree-cfg.c b/gcc/tree-cfg.c > index b75fdb2e63f..175b858f56b 100644 > --- a/gcc/tree-cfg.c > +++ b/gcc/tree-cfg.c > @@ -4121,8 +4121,11 @@ verify_gimple_assign_ternary (gassign *stmt) > return true; > } > > - if (((rhs_code == VEC_COND_EXPR || rhs_code == COND_EXPR) > - ? !is_gimple_condexpr (rhs1) : !is_gimple_val (rhs1)) > + if ((rhs_code == VEC_COND_EXPR > + ? !is_possibly_trapping_gimple_condexpr (rhs1) > + : (rhs_code == COND_EXPR > + ? !is_gimple_condexpr (rhs1) > + : !is_gimple_val (rhs1))) > || !is_gimple_val (rhs2) > || !is_gimple_val (rhs3)) > { > >> >> To go this route you'd have to split the is_gimple_condexpr check >> I guess and eventually users turning [VEC_]COND_EXPR into conditional >> code (do we have any?) have to be extra careful then. >> > > We have expand_vector_condition, which turns VEC_COND_EXPR into > COND_EXPR - but this should be harmless, right? I could not find > anything else. Ugh, I've realized I need to check not only VEC_COND_EXPR, but also COND_EXPR usages. There is, of course, a great deal more code, so I'm not sure whether I looked exhaustively through it, but there are at least store_expr and do_jump which do exactly this during expansion. Should we worry about EH edges at this point?
On Fri, Aug 30, 2019 at 5:25 PM Ilya Leoshkevich <iii@linux.ibm.com> wrote: > > > Am 30.08.2019 um 16:40 schrieb Ilya Leoshkevich <iii@linux.ibm.com>: > > > >> Am 30.08.2019 um 09:12 schrieb Richard Biener <richard.guenther@gmail.com>: > >> > >> On Thu, Aug 29, 2019 at 5:39 PM Ilya Leoshkevich <iii@linux.ibm.com> wrote: > >>> > >>>> Am 22.08.2019 um 15:45 schrieb Ilya Leoshkevich <iii@linux.ibm.com>: > >>>> > >>>> Bootstrap and regtest running on x86_64-redhat-linux and > >>>> s390x-redhat-linux. > >>>> > >>>> This patch series adds signaling FP comparison support (both scalar and > >>>> vector) to s390 backend. > >>> > >>> I'm running into a problem on ppc64 with this patch, and it would be > >>> great if someone could help me figure out the best way to resolve it. > >>> > >>> vector36.C test is failing because gimplifier produces the following > >>> > >>> _5 = _4 > { 2.0e+0, 2.0e+0, 2.0e+0, 2.0e+0 }; > >>> _6 = VEC_COND_EXPR <_5, { -1, -1, -1, -1 }, { 0, 0, 0, 0 }>; > >>> > >>> from > >>> > >>> VEC_COND_EXPR < (*b > { 2.0e+0, 2.0e+0, 2.0e+0, 2.0e+0 }) , > >>> { -1, -1, -1, -1 } , > >>> { 0, 0, 0, 0 } > > >>> > >>> Since the comparison tree code is now hidden behind a temporary, my code > >>> does not have anything to pass to the backend. The reason for creating > >>> a temporary is that the comparison can trap, and so the following check > >>> in gimplify_expr fails: > >>> > >>> if (gimple_seq_empty_p (internal_post) && (*gimple_test_f) (*expr_p)) > >>> goto out; > >>> > >>> gimple_test_f is is_gimple_condexpr, and it eventually calls > >>> operation_could_trap_p (GT). > >>> > >>> My current solution is to simply state that backend does not support > >>> SSA_NAME in vector comparisons, however, I don't like it, since it may > >>> cause performance regressions due to having to fall back to scalar > >>> comparisons. > >>> > >>> I was thinking about two other possible solutions: > >>> > >>> 1. Change the gimplifier to allow trapping vector comparisons. That's > >>> a bit complicated, because tree_could_throw_p checks not only for > >>> floating point traps, but also e.g. for array index out of bounds > >>> traps. So I would have to create a tree_could_throw_p version which > >>> disregards specific kinds of traps. > >>> > >>> 2. Change expand_vector_condition to follow SSA_NAME_DEF_STMT and use > >>> its tree_code instead of SSA_NAME. The potential problem I see with > >>> this is that there appears to be no guarantee that _5 will be inlined > >>> into _6 at a later point. So if we say that we don't need to fall > >>> back to scalar comparisons based on availability of vector > > >>> instruction and inlining does not happen, then what's actually will > >>> be required is vector selection (vsel on S/390), which might not be > >>> available in general case. > >>> > >>> What would be a better way to proceed here? > >> > >> On GIMPLE there isn't a good reason to split out trapping comparisons > >> from [VEC_]COND_EXPR - the gimplifier does this for GIMPLE_CONDs > >> where it is important because we'd have no way to represent EH info > >> when not done. It might be a bit awkward to preserve EH across RTL > >> expansion though in case the [VEC_]COND_EXPR are not expanded > >> as a single pattern, but I'm not sure. > > > > Ok, so I'm testing the following now - for the problematic test that > > helped: > > > > diff --git a/gcc/gimple-expr.c b/gcc/gimple-expr.c > > index b0c9f9b671a..940aa394769 100644 > > --- a/gcc/gimple-expr.c > > +++ b/gcc/gimple-expr.c > > @@ -602,17 +602,33 @@ is_gimple_lvalue (tree t) > > || TREE_CODE (t) == BIT_FIELD_REF); > > } > > > > -/* Return true if T is a GIMPLE condition. */ > > +/* Helper for is_gimple_condexpr and is_possibly_trapping_gimple_condexpr. */ > > > > -bool > > -is_gimple_condexpr (tree t) > > +static bool > > +is_gimple_condexpr_1 (tree t, bool allow_traps) > > { > > return (is_gimple_val (t) || (COMPARISON_CLASS_P (t) > > - && !tree_could_throw_p (t) > > + && (allow_traps || !tree_could_throw_p (t)) > > && is_gimple_val (TREE_OPERAND (t, 0)) > > && is_gimple_val (TREE_OPERAND (t, 1)))); > > } > > > > +/* Return true if T is a GIMPLE condition. */ > > + > > +bool > > +is_gimple_condexpr (tree t) > > +{ > > + return is_gimple_condexpr_1 (t, false); > > +} > > + > > +/* Like is_gimple_condexpr, but allow the T to trap. */ > > + > > +bool > > +is_possibly_trapping_gimple_condexpr (tree t) > > +{ > > + return is_gimple_condexpr_1 (t, true); > > +} > > + > > /* Return true if T is a gimple address. */ > > > > bool > > diff --git a/gcc/gimple-expr.h b/gcc/gimple-expr.h > > index 1ad1432bd17..20546ca5b99 100644 > > --- a/gcc/gimple-expr.h > > +++ b/gcc/gimple-expr.h > > @@ -41,6 +41,7 @@ extern void gimple_cond_get_ops_from_tree (tree, enum tree_code *, tree *, > > tree *); > > extern bool is_gimple_lvalue (tree); > > extern bool is_gimple_condexpr (tree); > > +extern bool is_possibly_trapping_gimple_condexpr (tree); > > extern bool is_gimple_address (const_tree); > > extern bool is_gimple_invariant_address (const_tree); > > extern bool is_gimple_ip_invariant_address (const_tree); > > diff --git a/gcc/gimplify.c b/gcc/gimplify.c > > index daa0b71c191..4e6256390c0 100644 > > --- a/gcc/gimplify.c > > +++ b/gcc/gimplify.c > > @@ -12973,6 +12973,7 @@ gimplify_expr (tree *expr_p, gimple_seq *pre_p, gimple_seq *post_p, > > else if (gimple_test_f == is_gimple_val > > || gimple_test_f == is_gimple_call_addr > > || gimple_test_f == is_gimple_condexpr > > + || gimple_test_f == is_possibly_trapping_gimple_condexpr > > || gimple_test_f == is_gimple_mem_rhs > > || gimple_test_f == is_gimple_mem_rhs_or_call > > || gimple_test_f == is_gimple_reg_rhs > > @@ -13814,7 +13815,7 @@ gimplify_expr (tree *expr_p, gimple_seq *pre_p, gimple_seq *post_p, > > enum gimplify_status r0, r1, r2; > > > > r0 = gimplify_expr (&TREE_OPERAND (*expr_p, 0), pre_p, > > - post_p, is_gimple_condexpr, fb_rvalue); > > + post_p, is_possibly_trapping_gimple_condexpr, fb_rvalue); > > r1 = gimplify_expr (&TREE_OPERAND (*expr_p, 1), pre_p, > > post_p, is_gimple_val, fb_rvalue); > > r2 = gimplify_expr (&TREE_OPERAND (*expr_p, 2), pre_p, > > diff --git a/gcc/tree-cfg.c b/gcc/tree-cfg.c > > index b75fdb2e63f..175b858f56b 100644 > > --- a/gcc/tree-cfg.c > > +++ b/gcc/tree-cfg.c > > @@ -4121,8 +4121,11 @@ verify_gimple_assign_ternary (gassign *stmt) > > return true; > > } > > > > - if (((rhs_code == VEC_COND_EXPR || rhs_code == COND_EXPR) > > - ? !is_gimple_condexpr (rhs1) : !is_gimple_val (rhs1)) > > + if ((rhs_code == VEC_COND_EXPR > > + ? !is_possibly_trapping_gimple_condexpr (rhs1) > > + : (rhs_code == COND_EXPR > > + ? !is_gimple_condexpr (rhs1) > > + : !is_gimple_val (rhs1))) > > || !is_gimple_val (rhs2) > > || !is_gimple_val (rhs3)) > > { > > > >> > >> To go this route you'd have to split the is_gimple_condexpr check > >> I guess and eventually users turning [VEC_]COND_EXPR into conditional > >> code (do we have any?) have to be extra careful then. > >> > > > > We have expand_vector_condition, which turns VEC_COND_EXPR into > > COND_EXPR - but this should be harmless, right? I could not find > > anything else. > > Ugh, I've realized I need to check not only VEC_COND_EXPR, but also > COND_EXPR usages. There is, of course, a great deal more code, so I'm > not sure whether I looked exhaustively through it, but there are at > least store_expr and do_jump which do exactly this during expansion. > Should we worry about EH edges at this point? Well, the EH edge needs to persist (and be rooted off the comparison, not the selection). That said, I'd simply stop using is_gimple_condexpr for GIMPLE_CONDs (it allows is_gimple_val which isn't proper form for GIMPLE_COND). Of course there's code using it for GIMPLE_CONDs which would need to be adjusted. Richard.
> Am 02.09.2019 um 12:37 schrieb Richard Biener <richard.guenther@gmail.com>: > > On Fri, Aug 30, 2019 at 5:25 PM Ilya Leoshkevich <iii@linux.ibm.com> wrote: >> >>> Am 30.08.2019 um 16:40 schrieb Ilya Leoshkevich <iii@linux.ibm.com>: >>> >>>> Am 30.08.2019 um 09:12 schrieb Richard Biener <richard.guenther@gmail.com>: >>>> >>>> On Thu, Aug 29, 2019 at 5:39 PM Ilya Leoshkevich <iii@linux.ibm.com> wrote: >>>>> >>>>>> Am 22.08.2019 um 15:45 schrieb Ilya Leoshkevich <iii@linux.ibm.com>: >>>>>> >>>>>> Bootstrap and regtest running on x86_64-redhat-linux and >>>>>> s390x-redhat-linux. >>>>>> >>>>>> This patch series adds signaling FP comparison support (both scalar and >>>>>> vector) to s390 backend. >>>>> >>>>> I'm running into a problem on ppc64 with this patch, and it would be >>>>> great if someone could help me figure out the best way to resolve it. >>>>> >>>>> vector36.C test is failing because gimplifier produces the following >>>>> >>>>> _5 = _4 > { 2.0e+0, 2.0e+0, 2.0e+0, 2.0e+0 }; >>>>> _6 = VEC_COND_EXPR <_5, { -1, -1, -1, -1 }, { 0, 0, 0, 0 }>; >>>>> >>>>> from >>>>> >>>>> VEC_COND_EXPR < (*b > { 2.0e+0, 2.0e+0, 2.0e+0, 2.0e+0 }) , >>>>> { -1, -1, -1, -1 } , >>>>> { 0, 0, 0, 0 } > >>>>> >>>>> Since the comparison tree code is now hidden behind a temporary, my code >>>>> does not have anything to pass to the backend. The reason for creating >>>>> a temporary is that the comparison can trap, and so the following check >>>>> in gimplify_expr fails: >>>>> >>>>> if (gimple_seq_empty_p (internal_post) && (*gimple_test_f) (*expr_p)) >>>>> goto out; >>>>> >>>>> gimple_test_f is is_gimple_condexpr, and it eventually calls >>>>> operation_could_trap_p (GT). >>>>> >>>>> My current solution is to simply state that backend does not support >>>>> SSA_NAME in vector comparisons, however, I don't like it, since it may >>>>> cause performance regressions due to having to fall back to scalar >>>>> comparisons. >>>>> >>>>> I was thinking about two other possible solutions: >>>>> >>>>> 1. Change the gimplifier to allow trapping vector comparisons. That's >>>>> a bit complicated, because tree_could_throw_p checks not only for >>>>> floating point traps, but also e.g. for array index out of bounds >>>>> traps. So I would have to create a tree_could_throw_p version which >>>>> disregards specific kinds of traps. >>>>> >>>>> 2. Change expand_vector_condition to follow SSA_NAME_DEF_STMT and use >>>>> its tree_code instead of SSA_NAME. The potential problem I see with >>>>> this is that there appears to be no guarantee that _5 will be inlined >>>>> into _6 at a later point. So if we say that we don't need to fall >>>>> back to scalar comparisons based on availability of vector > >>>>> instruction and inlining does not happen, then what's actually will >>>>> be required is vector selection (vsel on S/390), which might not be >>>>> available in general case. >>>>> >>>>> What would be a better way to proceed here? >>>> >>>> On GIMPLE there isn't a good reason to split out trapping comparisons >>>> from [VEC_]COND_EXPR - the gimplifier does this for GIMPLE_CONDs >>>> where it is important because we'd have no way to represent EH info >>>> when not done. It might be a bit awkward to preserve EH across RTL >>>> expansion though in case the [VEC_]COND_EXPR are not expanded >>>> as a single pattern, but I'm not sure. >>> >>> Ok, so I'm testing the following now - for the problematic test that >>> helped: >>> >>> diff --git a/gcc/gimple-expr.c b/gcc/gimple-expr.c >>> index b0c9f9b671a..940aa394769 100644 >>> --- a/gcc/gimple-expr.c >>> +++ b/gcc/gimple-expr.c >>> @@ -602,17 +602,33 @@ is_gimple_lvalue (tree t) >>> || TREE_CODE (t) == BIT_FIELD_REF); >>> } >>> >>> -/* Return true if T is a GIMPLE condition. */ >>> +/* Helper for is_gimple_condexpr and is_possibly_trapping_gimple_condexpr. */ >>> >>> -bool >>> -is_gimple_condexpr (tree t) >>> +static bool >>> +is_gimple_condexpr_1 (tree t, bool allow_traps) >>> { >>> return (is_gimple_val (t) || (COMPARISON_CLASS_P (t) >>> - && !tree_could_throw_p (t) >>> + && (allow_traps || !tree_could_throw_p (t)) >>> && is_gimple_val (TREE_OPERAND (t, 0)) >>> && is_gimple_val (TREE_OPERAND (t, 1)))); >>> } >>> >>> +/* Return true if T is a GIMPLE condition. */ >>> + >>> +bool >>> +is_gimple_condexpr (tree t) >>> +{ >>> + return is_gimple_condexpr_1 (t, false); >>> +} >>> + >>> +/* Like is_gimple_condexpr, but allow the T to trap. */ >>> + >>> +bool >>> +is_possibly_trapping_gimple_condexpr (tree t) >>> +{ >>> + return is_gimple_condexpr_1 (t, true); >>> +} >>> + >>> /* Return true if T is a gimple address. */ >>> >>> bool >>> diff --git a/gcc/gimple-expr.h b/gcc/gimple-expr.h >>> index 1ad1432bd17..20546ca5b99 100644 >>> --- a/gcc/gimple-expr.h >>> +++ b/gcc/gimple-expr.h >>> @@ -41,6 +41,7 @@ extern void gimple_cond_get_ops_from_tree (tree, enum tree_code *, tree *, >>> tree *); >>> extern bool is_gimple_lvalue (tree); >>> extern bool is_gimple_condexpr (tree); >>> +extern bool is_possibly_trapping_gimple_condexpr (tree); >>> extern bool is_gimple_address (const_tree); >>> extern bool is_gimple_invariant_address (const_tree); >>> extern bool is_gimple_ip_invariant_address (const_tree); >>> diff --git a/gcc/gimplify.c b/gcc/gimplify.c >>> index daa0b71c191..4e6256390c0 100644 >>> --- a/gcc/gimplify.c >>> +++ b/gcc/gimplify.c >>> @@ -12973,6 +12973,7 @@ gimplify_expr (tree *expr_p, gimple_seq *pre_p, gimple_seq *post_p, >>> else if (gimple_test_f == is_gimple_val >>> || gimple_test_f == is_gimple_call_addr >>> || gimple_test_f == is_gimple_condexpr >>> + || gimple_test_f == is_possibly_trapping_gimple_condexpr >>> || gimple_test_f == is_gimple_mem_rhs >>> || gimple_test_f == is_gimple_mem_rhs_or_call >>> || gimple_test_f == is_gimple_reg_rhs >>> @@ -13814,7 +13815,7 @@ gimplify_expr (tree *expr_p, gimple_seq *pre_p, gimple_seq *post_p, >>> enum gimplify_status r0, r1, r2; >>> >>> r0 = gimplify_expr (&TREE_OPERAND (*expr_p, 0), pre_p, >>> - post_p, is_gimple_condexpr, fb_rvalue); >>> + post_p, is_possibly_trapping_gimple_condexpr, fb_rvalue); >>> r1 = gimplify_expr (&TREE_OPERAND (*expr_p, 1), pre_p, >>> post_p, is_gimple_val, fb_rvalue); >>> r2 = gimplify_expr (&TREE_OPERAND (*expr_p, 2), pre_p, >>> diff --git a/gcc/tree-cfg.c b/gcc/tree-cfg.c >>> index b75fdb2e63f..175b858f56b 100644 >>> --- a/gcc/tree-cfg.c >>> +++ b/gcc/tree-cfg.c >>> @@ -4121,8 +4121,11 @@ verify_gimple_assign_ternary (gassign *stmt) >>> return true; >>> } >>> >>> - if (((rhs_code == VEC_COND_EXPR || rhs_code == COND_EXPR) >>> - ? !is_gimple_condexpr (rhs1) : !is_gimple_val (rhs1)) >>> + if ((rhs_code == VEC_COND_EXPR >>> + ? !is_possibly_trapping_gimple_condexpr (rhs1) >>> + : (rhs_code == COND_EXPR >>> + ? !is_gimple_condexpr (rhs1) >>> + : !is_gimple_val (rhs1))) >>> || !is_gimple_val (rhs2) >>> || !is_gimple_val (rhs3)) >>> { >>> >>>> >>>> To go this route you'd have to split the is_gimple_condexpr check >>>> I guess and eventually users turning [VEC_]COND_EXPR into conditional >>>> code (do we have any?) have to be extra careful then. >>>> >>> >>> We have expand_vector_condition, which turns VEC_COND_EXPR into >>> COND_EXPR - but this should be harmless, right? I could not find >>> anything else. >> >> Ugh, I've realized I need to check not only VEC_COND_EXPR, but also >> COND_EXPR usages. There is, of course, a great deal more code, so I'm >> not sure whether I looked exhaustively through it, but there are at >> least store_expr and do_jump which do exactly this during expansion. >> Should we worry about EH edges at this point? > > Well, the EH edge needs to persist (and be rooted off the comparison, > not the selection). Ok, I'm trying to create some samples that may reveal problems with EH edges in these two cases. So far with these experiments I only managed to find and unrelated S/390 bug :-) https://gcc.gnu.org/ml/gcc-patches/2019-09/msg00065.html > That said, I'd simply stop using is_gimple_condexpr for GIMPLE_CONDs > (it allows is_gimple_val which isn't proper form for GIMPLE_COND). Of course > there's code using it for GIMPLE_CONDs which would need to be adjusted. I'm sorry, I don't quite get this - what would that buy us? and what would you use instead? Right now we fix up non-conforming values accepted by is_gimple_val using gimple_cond_get_ops_from_tree - is there a problem with this approach? What I have in mind right now is to: - allow trapping conditions for COND_EXPR and VEC_COND_EXPR; - report them as trapping in operation_could_trap_p and tree_could_trap_p iff their condition is trapping; - find and adjust all places where this messes up EH edges. GIMPLE_COND logic appears to be already covered precisely because it uses is_gimple_condexpr. Am I missing something?
On Mon, Sep 2, 2019 at 6:28 PM Ilya Leoshkevich <iii@linux.ibm.com> wrote: > > > Am 02.09.2019 um 12:37 schrieb Richard Biener <richard.guenther@gmail.com>: > > > > On Fri, Aug 30, 2019 at 5:25 PM Ilya Leoshkevich <iii@linux.ibm.com> wrote: > >> > >>> Am 30.08.2019 um 16:40 schrieb Ilya Leoshkevich <iii@linux.ibm.com>: > >>> > >>>> Am 30.08.2019 um 09:12 schrieb Richard Biener <richard.guenther@gmail.com>: > >>>> > >>>> On Thu, Aug 29, 2019 at 5:39 PM Ilya Leoshkevich <iii@linux.ibm.com> wrote: > >>>>> > >>>>>> Am 22.08.2019 um 15:45 schrieb Ilya Leoshkevich <iii@linux.ibm.com>: > >>>>>> > >>>>>> Bootstrap and regtest running on x86_64-redhat-linux and > >>>>>> s390x-redhat-linux. > >>>>>> > >>>>>> This patch series adds signaling FP comparison support (both scalar and > >>>>>> vector) to s390 backend. > >>>>> > >>>>> I'm running into a problem on ppc64 with this patch, and it would be > >>>>> great if someone could help me figure out the best way to resolve it. > >>>>> > >>>>> vector36.C test is failing because gimplifier produces the following > >>>>> > >>>>> _5 = _4 > { 2.0e+0, 2.0e+0, 2.0e+0, 2.0e+0 }; > >>>>> _6 = VEC_COND_EXPR <_5, { -1, -1, -1, -1 }, { 0, 0, 0, 0 }>; > >>>>> > >>>>> from > >>>>> > >>>>> VEC_COND_EXPR < (*b > { 2.0e+0, 2.0e+0, 2.0e+0, 2.0e+0 }) , > >>>>> { -1, -1, -1, -1 } , > >>>>> { 0, 0, 0, 0 } > > >>>>> > >>>>> Since the comparison tree code is now hidden behind a temporary, my code > >>>>> does not have anything to pass to the backend. The reason for creating > >>>>> a temporary is that the comparison can trap, and so the following check > >>>>> in gimplify_expr fails: > >>>>> > >>>>> if (gimple_seq_empty_p (internal_post) && (*gimple_test_f) (*expr_p)) > >>>>> goto out; > >>>>> > >>>>> gimple_test_f is is_gimple_condexpr, and it eventually calls > >>>>> operation_could_trap_p (GT). > >>>>> > >>>>> My current solution is to simply state that backend does not support > >>>>> SSA_NAME in vector comparisons, however, I don't like it, since it may > >>>>> cause performance regressions due to having to fall back to scalar > >>>>> comparisons. > >>>>> > >>>>> I was thinking about two other possible solutions: > >>>>> > >>>>> 1. Change the gimplifier to allow trapping vector comparisons. That's > >>>>> a bit complicated, because tree_could_throw_p checks not only for > >>>>> floating point traps, but also e.g. for array index out of bounds > >>>>> traps. So I would have to create a tree_could_throw_p version which > >>>>> disregards specific kinds of traps. > >>>>> > >>>>> 2. Change expand_vector_condition to follow SSA_NAME_DEF_STMT and use > >>>>> its tree_code instead of SSA_NAME. The potential problem I see with > >>>>> this is that there appears to be no guarantee that _5 will be inlined > >>>>> into _6 at a later point. So if we say that we don't need to fall > >>>>> back to scalar comparisons based on availability of vector > > >>>>> instruction and inlining does not happen, then what's actually will > >>>>> be required is vector selection (vsel on S/390), which might not be > >>>>> available in general case. > >>>>> > >>>>> What would be a better way to proceed here? > >>>> > >>>> On GIMPLE there isn't a good reason to split out trapping comparisons > >>>> from [VEC_]COND_EXPR - the gimplifier does this for GIMPLE_CONDs > >>>> where it is important because we'd have no way to represent EH info > >>>> when not done. It might be a bit awkward to preserve EH across RTL > >>>> expansion though in case the [VEC_]COND_EXPR are not expanded > >>>> as a single pattern, but I'm not sure. > >>> > >>> Ok, so I'm testing the following now - for the problematic test that > >>> helped: > >>> > >>> diff --git a/gcc/gimple-expr.c b/gcc/gimple-expr.c > >>> index b0c9f9b671a..940aa394769 100644 > >>> --- a/gcc/gimple-expr.c > >>> +++ b/gcc/gimple-expr.c > >>> @@ -602,17 +602,33 @@ is_gimple_lvalue (tree t) > >>> || TREE_CODE (t) == BIT_FIELD_REF); > >>> } > >>> > >>> -/* Return true if T is a GIMPLE condition. */ > >>> +/* Helper for is_gimple_condexpr and is_possibly_trapping_gimple_condexpr. */ > >>> > >>> -bool > >>> -is_gimple_condexpr (tree t) > >>> +static bool > >>> +is_gimple_condexpr_1 (tree t, bool allow_traps) > >>> { > >>> return (is_gimple_val (t) || (COMPARISON_CLASS_P (t) > >>> - && !tree_could_throw_p (t) > >>> + && (allow_traps || !tree_could_throw_p (t)) > >>> && is_gimple_val (TREE_OPERAND (t, 0)) > >>> && is_gimple_val (TREE_OPERAND (t, 1)))); > >>> } > >>> > >>> +/* Return true if T is a GIMPLE condition. */ > >>> + > >>> +bool > >>> +is_gimple_condexpr (tree t) > >>> +{ > >>> + return is_gimple_condexpr_1 (t, false); > >>> +} > >>> + > >>> +/* Like is_gimple_condexpr, but allow the T to trap. */ > >>> + > >>> +bool > >>> +is_possibly_trapping_gimple_condexpr (tree t) > >>> +{ > >>> + return is_gimple_condexpr_1 (t, true); > >>> +} > >>> + > >>> /* Return true if T is a gimple address. */ > >>> > >>> bool > >>> diff --git a/gcc/gimple-expr.h b/gcc/gimple-expr.h > >>> index 1ad1432bd17..20546ca5b99 100644 > >>> --- a/gcc/gimple-expr.h > >>> +++ b/gcc/gimple-expr.h > >>> @@ -41,6 +41,7 @@ extern void gimple_cond_get_ops_from_tree (tree, enum tree_code *, tree *, > >>> tree *); > >>> extern bool is_gimple_lvalue (tree); > >>> extern bool is_gimple_condexpr (tree); > >>> +extern bool is_possibly_trapping_gimple_condexpr (tree); > >>> extern bool is_gimple_address (const_tree); > >>> extern bool is_gimple_invariant_address (const_tree); > >>> extern bool is_gimple_ip_invariant_address (const_tree); > >>> diff --git a/gcc/gimplify.c b/gcc/gimplify.c > >>> index daa0b71c191..4e6256390c0 100644 > >>> --- a/gcc/gimplify.c > >>> +++ b/gcc/gimplify.c > >>> @@ -12973,6 +12973,7 @@ gimplify_expr (tree *expr_p, gimple_seq *pre_p, gimple_seq *post_p, > >>> else if (gimple_test_f == is_gimple_val > >>> || gimple_test_f == is_gimple_call_addr > >>> || gimple_test_f == is_gimple_condexpr > >>> + || gimple_test_f == is_possibly_trapping_gimple_condexpr > >>> || gimple_test_f == is_gimple_mem_rhs > >>> || gimple_test_f == is_gimple_mem_rhs_or_call > >>> || gimple_test_f == is_gimple_reg_rhs > >>> @@ -13814,7 +13815,7 @@ gimplify_expr (tree *expr_p, gimple_seq *pre_p, gimple_seq *post_p, > >>> enum gimplify_status r0, r1, r2; > >>> > >>> r0 = gimplify_expr (&TREE_OPERAND (*expr_p, 0), pre_p, > >>> - post_p, is_gimple_condexpr, fb_rvalue); > >>> + post_p, is_possibly_trapping_gimple_condexpr, fb_rvalue); > >>> r1 = gimplify_expr (&TREE_OPERAND (*expr_p, 1), pre_p, > >>> post_p, is_gimple_val, fb_rvalue); > >>> r2 = gimplify_expr (&TREE_OPERAND (*expr_p, 2), pre_p, > >>> diff --git a/gcc/tree-cfg.c b/gcc/tree-cfg.c > >>> index b75fdb2e63f..175b858f56b 100644 > >>> --- a/gcc/tree-cfg.c > >>> +++ b/gcc/tree-cfg.c > >>> @@ -4121,8 +4121,11 @@ verify_gimple_assign_ternary (gassign *stmt) > >>> return true; > >>> } > >>> > >>> - if (((rhs_code == VEC_COND_EXPR || rhs_code == COND_EXPR) > >>> - ? !is_gimple_condexpr (rhs1) : !is_gimple_val (rhs1)) > >>> + if ((rhs_code == VEC_COND_EXPR > >>> + ? !is_possibly_trapping_gimple_condexpr (rhs1) > >>> + : (rhs_code == COND_EXPR > >>> + ? !is_gimple_condexpr (rhs1) > >>> + : !is_gimple_val (rhs1))) > >>> || !is_gimple_val (rhs2) > >>> || !is_gimple_val (rhs3)) > >>> { > >>> > >>>> > >>>> To go this route you'd have to split the is_gimple_condexpr check > >>>> I guess and eventually users turning [VEC_]COND_EXPR into conditional > >>>> code (do we have any?) have to be extra careful then. > >>>> > >>> > >>> We have expand_vector_condition, which turns VEC_COND_EXPR into > >>> COND_EXPR - but this should be harmless, right? I could not find > >>> anything else. > >> > >> Ugh, I've realized I need to check not only VEC_COND_EXPR, but also > >> COND_EXPR usages. There is, of course, a great deal more code, so I'm > >> not sure whether I looked exhaustively through it, but there are at > >> least store_expr and do_jump which do exactly this during expansion. > >> Should we worry about EH edges at this point? > > > > Well, the EH edge needs to persist (and be rooted off the comparison, > > not the selection). > > Ok, I'm trying to create some samples that may reveal problems with EH > edges in these two cases. So far with these experiments I only managed > to find and unrelated S/390 bug :-) > https://gcc.gnu.org/ml/gcc-patches/2019-09/msg00065.html > > > That said, I'd simply stop using is_gimple_condexpr for GIMPLE_CONDs > > (it allows is_gimple_val which isn't proper form for GIMPLE_COND). Of course > > there's code using it for GIMPLE_CONDs which would need to be adjusted. > > I'm sorry, I don't quite get this - what would that buy us? and what > would you use instead? Right now we fix up non-conforming values > accepted by is_gimple_val using gimple_cond_get_ops_from_tree - is > there a problem with this approach? > > What I have in mind right now is to: > - allow trapping conditions for COND_EXPR and VEC_COND_EXPR; > - report them as trapping in operation_could_trap_p and > tree_could_trap_p iff their condition is trapping; > - find and adjust all places where this messes up EH edges. > > GIMPLE_COND logic appears to be already covered precisely because it > uses is_gimple_condexpr. > > Am I missing something? Not really - all I'm saying is that currently we use is_gimple_condexpr to check whether a GENERIC tree is suitable for [VEC_]COND_EXPR during for example forward propagation. And GIMPLE_COND already uses its own logic (as you say) but still passes use is_gimple_condexpr for it. So my proposal would be to change is_gimple_condexpr to allow trapping [VEC_]COND_EXPR and stop using is_gimple_condexpr checks on conditions to be used for GIMPLE_CONDs (and substitute another predicate there). For this to work and catch wrong-doings we should amend gimple_cond_get_ops_from_tree to assert that the extracted condition cannot trap. Richard.
> Am 03.09.2019 um 12:07 schrieb Richard Biener <richard.guenther@gmail.com>: > > On Mon, Sep 2, 2019 at 6:28 PM Ilya Leoshkevich <iii@linux.ibm.com> wrote: >> >>> Am 02.09.2019 um 12:37 schrieb Richard Biener <richard.guenther@gmail.com>: >>> >>> On Fri, Aug 30, 2019 at 5:25 PM Ilya Leoshkevich <iii@linux.ibm.com> wrote: >>>> >>>>> Am 30.08.2019 um 16:40 schrieb Ilya Leoshkevich <iii@linux.ibm.com>: >>>>> >>>>>> Am 30.08.2019 um 09:12 schrieb Richard Biener <richard.guenther@gmail.com>: >>>>>> >>>>>> On Thu, Aug 29, 2019 at 5:39 PM Ilya Leoshkevich <iii@linux.ibm.com> wrote: >>>>>>> >>>>>>>> Am 22.08.2019 um 15:45 schrieb Ilya Leoshkevich <iii@linux.ibm.com>: >>>>>>>> >>>>>>>> Bootstrap and regtest running on x86_64-redhat-linux and >>>>>>>> s390x-redhat-linux. >>>>>>>> >>>>>>>> This patch series adds signaling FP comparison support (both scalar and >>>>>>>> vector) to s390 backend. >>>>>>> >>>>>>> I'm running into a problem on ppc64 with this patch, and it would be >>>>>>> great if someone could help me figure out the best way to resolve it. >>>>>>> >>>>>>> vector36.C test is failing because gimplifier produces the following >>>>>>> >>>>>>> _5 = _4 > { 2.0e+0, 2.0e+0, 2.0e+0, 2.0e+0 }; >>>>>>> _6 = VEC_COND_EXPR <_5, { -1, -1, -1, -1 }, { 0, 0, 0, 0 }>; >>>>>>> >>>>>>> from >>>>>>> >>>>>>> VEC_COND_EXPR < (*b > { 2.0e+0, 2.0e+0, 2.0e+0, 2.0e+0 }) , >>>>>>> { -1, -1, -1, -1 } , >>>>>>> { 0, 0, 0, 0 } > >>>>>>> >>>>>>> Since the comparison tree code is now hidden behind a temporary, my code >>>>>>> does not have anything to pass to the backend. The reason for creating >>>>>>> a temporary is that the comparison can trap, and so the following check >>>>>>> in gimplify_expr fails: >>>>>>> >>>>>>> if (gimple_seq_empty_p (internal_post) && (*gimple_test_f) (*expr_p)) >>>>>>> goto out; >>>>>>> >>>>>>> gimple_test_f is is_gimple_condexpr, and it eventually calls >>>>>>> operation_could_trap_p (GT). >>>>>>> >>>>>>> My current solution is to simply state that backend does not support >>>>>>> SSA_NAME in vector comparisons, however, I don't like it, since it may >>>>>>> cause performance regressions due to having to fall back to scalar >>>>>>> comparisons. >>>>>>> >>>>>>> I was thinking about two other possible solutions: >>>>>>> >>>>>>> 1. Change the gimplifier to allow trapping vector comparisons. That's >>>>>>> a bit complicated, because tree_could_throw_p checks not only for >>>>>>> floating point traps, but also e.g. for array index out of bounds >>>>>>> traps. So I would have to create a tree_could_throw_p version which >>>>>>> disregards specific kinds of traps. >>>>>>> >>>>>>> 2. Change expand_vector_condition to follow SSA_NAME_DEF_STMT and use >>>>>>> its tree_code instead of SSA_NAME. The potential problem I see with >>>>>>> this is that there appears to be no guarantee that _5 will be inlined >>>>>>> into _6 at a later point. So if we say that we don't need to fall >>>>>>> back to scalar comparisons based on availability of vector > >>>>>>> instruction and inlining does not happen, then what's actually will >>>>>>> be required is vector selection (vsel on S/390), which might not be >>>>>>> available in general case. >>>>>>> >>>>>>> What would be a better way to proceed here? >>>>>> >>>>>> On GIMPLE there isn't a good reason to split out trapping comparisons >>>>>> from [VEC_]COND_EXPR - the gimplifier does this for GIMPLE_CONDs >>>>>> where it is important because we'd have no way to represent EH info >>>>>> when not done. It might be a bit awkward to preserve EH across RTL >>>>>> expansion though in case the [VEC_]COND_EXPR are not expanded >>>>>> as a single pattern, but I'm not sure. >>>>> >>>>> Ok, so I'm testing the following now - for the problematic test that >>>>> helped: >>>>> >>>>> diff --git a/gcc/gimple-expr.c b/gcc/gimple-expr.c >>>>> index b0c9f9b671a..940aa394769 100644 >>>>> --- a/gcc/gimple-expr.c >>>>> +++ b/gcc/gimple-expr.c >>>>> @@ -602,17 +602,33 @@ is_gimple_lvalue (tree t) >>>>> || TREE_CODE (t) == BIT_FIELD_REF); >>>>> } >>>>> >>>>> -/* Return true if T is a GIMPLE condition. */ >>>>> +/* Helper for is_gimple_condexpr and is_possibly_trapping_gimple_condexpr. */ >>>>> >>>>> -bool >>>>> -is_gimple_condexpr (tree t) >>>>> +static bool >>>>> +is_gimple_condexpr_1 (tree t, bool allow_traps) >>>>> { >>>>> return (is_gimple_val (t) || (COMPARISON_CLASS_P (t) >>>>> - && !tree_could_throw_p (t) >>>>> + && (allow_traps || !tree_could_throw_p (t)) >>>>> && is_gimple_val (TREE_OPERAND (t, 0)) >>>>> && is_gimple_val (TREE_OPERAND (t, 1)))); >>>>> } >>>>> >>>>> +/* Return true if T is a GIMPLE condition. */ >>>>> + >>>>> +bool >>>>> +is_gimple_condexpr (tree t) >>>>> +{ >>>>> + return is_gimple_condexpr_1 (t, false); >>>>> +} >>>>> + >>>>> +/* Like is_gimple_condexpr, but allow the T to trap. */ >>>>> + >>>>> +bool >>>>> +is_possibly_trapping_gimple_condexpr (tree t) >>>>> +{ >>>>> + return is_gimple_condexpr_1 (t, true); >>>>> +} >>>>> + >>>>> /* Return true if T is a gimple address. */ >>>>> >>>>> bool >>>>> diff --git a/gcc/gimple-expr.h b/gcc/gimple-expr.h >>>>> index 1ad1432bd17..20546ca5b99 100644 >>>>> --- a/gcc/gimple-expr.h >>>>> +++ b/gcc/gimple-expr.h >>>>> @@ -41,6 +41,7 @@ extern void gimple_cond_get_ops_from_tree (tree, enum tree_code *, tree *, >>>>> tree *); >>>>> extern bool is_gimple_lvalue (tree); >>>>> extern bool is_gimple_condexpr (tree); >>>>> +extern bool is_possibly_trapping_gimple_condexpr (tree); >>>>> extern bool is_gimple_address (const_tree); >>>>> extern bool is_gimple_invariant_address (const_tree); >>>>> extern bool is_gimple_ip_invariant_address (const_tree); >>>>> diff --git a/gcc/gimplify.c b/gcc/gimplify.c >>>>> index daa0b71c191..4e6256390c0 100644 >>>>> --- a/gcc/gimplify.c >>>>> +++ b/gcc/gimplify.c >>>>> @@ -12973,6 +12973,7 @@ gimplify_expr (tree *expr_p, gimple_seq *pre_p, gimple_seq *post_p, >>>>> else if (gimple_test_f == is_gimple_val >>>>> || gimple_test_f == is_gimple_call_addr >>>>> || gimple_test_f == is_gimple_condexpr >>>>> + || gimple_test_f == is_possibly_trapping_gimple_condexpr >>>>> || gimple_test_f == is_gimple_mem_rhs >>>>> || gimple_test_f == is_gimple_mem_rhs_or_call >>>>> || gimple_test_f == is_gimple_reg_rhs >>>>> @@ -13814,7 +13815,7 @@ gimplify_expr (tree *expr_p, gimple_seq *pre_p, gimple_seq *post_p, >>>>> enum gimplify_status r0, r1, r2; >>>>> >>>>> r0 = gimplify_expr (&TREE_OPERAND (*expr_p, 0), pre_p, >>>>> - post_p, is_gimple_condexpr, fb_rvalue); >>>>> + post_p, is_possibly_trapping_gimple_condexpr, fb_rvalue); >>>>> r1 = gimplify_expr (&TREE_OPERAND (*expr_p, 1), pre_p, >>>>> post_p, is_gimple_val, fb_rvalue); >>>>> r2 = gimplify_expr (&TREE_OPERAND (*expr_p, 2), pre_p, >>>>> diff --git a/gcc/tree-cfg.c b/gcc/tree-cfg.c >>>>> index b75fdb2e63f..175b858f56b 100644 >>>>> --- a/gcc/tree-cfg.c >>>>> +++ b/gcc/tree-cfg.c >>>>> @@ -4121,8 +4121,11 @@ verify_gimple_assign_ternary (gassign *stmt) >>>>> return true; >>>>> } >>>>> >>>>> - if (((rhs_code == VEC_COND_EXPR || rhs_code == COND_EXPR) >>>>> - ? !is_gimple_condexpr (rhs1) : !is_gimple_val (rhs1)) >>>>> + if ((rhs_code == VEC_COND_EXPR >>>>> + ? !is_possibly_trapping_gimple_condexpr (rhs1) >>>>> + : (rhs_code == COND_EXPR >>>>> + ? !is_gimple_condexpr (rhs1) >>>>> + : !is_gimple_val (rhs1))) >>>>> || !is_gimple_val (rhs2) >>>>> || !is_gimple_val (rhs3)) >>>>> { >>>>> >>>>>> >>>>>> To go this route you'd have to split the is_gimple_condexpr check >>>>>> I guess and eventually users turning [VEC_]COND_EXPR into conditional >>>>>> code (do we have any?) have to be extra careful then. >>>>>> >>>>> >>>>> We have expand_vector_condition, which turns VEC_COND_EXPR into >>>>> COND_EXPR - but this should be harmless, right? I could not find >>>>> anything else. >>>> >>>> Ugh, I've realized I need to check not only VEC_COND_EXPR, but also >>>> COND_EXPR usages. There is, of course, a great deal more code, so I'm >>>> not sure whether I looked exhaustively through it, but there are at >>>> least store_expr and do_jump which do exactly this during expansion. >>>> Should we worry about EH edges at this point? >>> >>> Well, the EH edge needs to persist (and be rooted off the comparison, >>> not the selection). >> >> Ok, I'm trying to create some samples that may reveal problems with EH >> edges in these two cases. So far with these experiments I only managed >> to find and unrelated S/390 bug :-) >> https://gcc.gnu.org/ml/gcc-patches/2019-09/msg00065.html >> >>> That said, I'd simply stop using is_gimple_condexpr for GIMPLE_CONDs >>> (it allows is_gimple_val which isn't proper form for GIMPLE_COND). Of course >>> there's code using it for GIMPLE_CONDs which would need to be adjusted. >> >> I'm sorry, I don't quite get this - what would that buy us? and what >> would you use instead? Right now we fix up non-conforming values >> accepted by is_gimple_val using gimple_cond_get_ops_from_tree - is >> there a problem with this approach? >> >> What I have in mind right now is to: >> - allow trapping conditions for COND_EXPR and VEC_COND_EXPR; >> - report them as trapping in operation_could_trap_p and >> tree_could_trap_p iff their condition is trapping; >> - find and adjust all places where this messes up EH edges. >> >> GIMPLE_COND logic appears to be already covered precisely because it >> uses is_gimple_condexpr. >> >> Am I missing something? > > Not really - all I'm saying is that currently we use is_gimple_condexpr > to check whether a GENERIC tree is suitable for [VEC_]COND_EXPR > during for example forward propagation. > > And GIMPLE_COND already uses its own logic (as you say) but > still passes use is_gimple_condexpr for it. > > So my proposal would be to change is_gimple_condexpr to > allow trapping [VEC_]COND_EXPR and stop using is_gimple_condexpr > checks on conditions to be used for GIMPLE_CONDs (and substitute > another predicate there). For this to work and catch wrong-doings > we should amend gimple_cond_get_ops_from_tree to assert > that the extracted condition cannot trap. Ah, I think now I understand. While I wanted to keep is_gimple_condexpr as is and introduce is_possibly_trapping_gimple_condexpr, you're saying we rather need to change is_gimple_condexpr and introduce, say, is_non_trapping_gimple_condexpr. This makes sense, thanks for the explanation!
On Tue, Sep 3, 2019 at 12:34 PM Ilya Leoshkevich <iii@linux.ibm.com> wrote: > > > Am 03.09.2019 um 12:07 schrieb Richard Biener <richard.guenther@gmail.com>: > > > > On Mon, Sep 2, 2019 at 6:28 PM Ilya Leoshkevich <iii@linux.ibm.com> wrote: > >> > >>> Am 02.09.2019 um 12:37 schrieb Richard Biener <richard.guenther@gmail.com>: > >>> > >>> On Fri, Aug 30, 2019 at 5:25 PM Ilya Leoshkevich <iii@linux.ibm.com> wrote: > >>>> > >>>>> Am 30.08.2019 um 16:40 schrieb Ilya Leoshkevich <iii@linux.ibm.com>: > >>>>> > >>>>>> Am 30.08.2019 um 09:12 schrieb Richard Biener <richard.guenther@gmail.com>: > >>>>>> > >>>>>> On Thu, Aug 29, 2019 at 5:39 PM Ilya Leoshkevich <iii@linux.ibm.com> wrote: > >>>>>>> > >>>>>>>> Am 22.08.2019 um 15:45 schrieb Ilya Leoshkevich <iii@linux.ibm.com>: > >>>>>>>> > >>>>>>>> Bootstrap and regtest running on x86_64-redhat-linux and > >>>>>>>> s390x-redhat-linux. > >>>>>>>> > >>>>>>>> This patch series adds signaling FP comparison support (both scalar and > >>>>>>>> vector) to s390 backend. > >>>>>>> > >>>>>>> I'm running into a problem on ppc64 with this patch, and it would be > >>>>>>> great if someone could help me figure out the best way to resolve it. > >>>>>>> > >>>>>>> vector36.C test is failing because gimplifier produces the following > >>>>>>> > >>>>>>> _5 = _4 > { 2.0e+0, 2.0e+0, 2.0e+0, 2.0e+0 }; > >>>>>>> _6 = VEC_COND_EXPR <_5, { -1, -1, -1, -1 }, { 0, 0, 0, 0 }>; > >>>>>>> > >>>>>>> from > >>>>>>> > >>>>>>> VEC_COND_EXPR < (*b > { 2.0e+0, 2.0e+0, 2.0e+0, 2.0e+0 }) , > >>>>>>> { -1, -1, -1, -1 } , > >>>>>>> { 0, 0, 0, 0 } > > >>>>>>> > >>>>>>> Since the comparison tree code is now hidden behind a temporary, my code > >>>>>>> does not have anything to pass to the backend. The reason for creating > >>>>>>> a temporary is that the comparison can trap, and so the following check > >>>>>>> in gimplify_expr fails: > >>>>>>> > >>>>>>> if (gimple_seq_empty_p (internal_post) && (*gimple_test_f) (*expr_p)) > >>>>>>> goto out; > >>>>>>> > >>>>>>> gimple_test_f is is_gimple_condexpr, and it eventually calls > >>>>>>> operation_could_trap_p (GT). > >>>>>>> > >>>>>>> My current solution is to simply state that backend does not support > >>>>>>> SSA_NAME in vector comparisons, however, I don't like it, since it may > >>>>>>> cause performance regressions due to having to fall back to scalar > >>>>>>> comparisons. > >>>>>>> > >>>>>>> I was thinking about two other possible solutions: > >>>>>>> > >>>>>>> 1. Change the gimplifier to allow trapping vector comparisons. That's > >>>>>>> a bit complicated, because tree_could_throw_p checks not only for > >>>>>>> floating point traps, but also e.g. for array index out of bounds > >>>>>>> traps. So I would have to create a tree_could_throw_p version which > >>>>>>> disregards specific kinds of traps. > >>>>>>> > >>>>>>> 2. Change expand_vector_condition to follow SSA_NAME_DEF_STMT and use > >>>>>>> its tree_code instead of SSA_NAME. The potential problem I see with > >>>>>>> this is that there appears to be no guarantee that _5 will be inlined > >>>>>>> into _6 at a later point. So if we say that we don't need to fall > >>>>>>> back to scalar comparisons based on availability of vector > > >>>>>>> instruction and inlining does not happen, then what's actually will > >>>>>>> be required is vector selection (vsel on S/390), which might not be > >>>>>>> available in general case. > >>>>>>> > >>>>>>> What would be a better way to proceed here? > >>>>>> > >>>>>> On GIMPLE there isn't a good reason to split out trapping comparisons > >>>>>> from [VEC_]COND_EXPR - the gimplifier does this for GIMPLE_CONDs > >>>>>> where it is important because we'd have no way to represent EH info > >>>>>> when not done. It might be a bit awkward to preserve EH across RTL > >>>>>> expansion though in case the [VEC_]COND_EXPR are not expanded > >>>>>> as a single pattern, but I'm not sure. > >>>>> > >>>>> Ok, so I'm testing the following now - for the problematic test that > >>>>> helped: > >>>>> > >>>>> diff --git a/gcc/gimple-expr.c b/gcc/gimple-expr.c > >>>>> index b0c9f9b671a..940aa394769 100644 > >>>>> --- a/gcc/gimple-expr.c > >>>>> +++ b/gcc/gimple-expr.c > >>>>> @@ -602,17 +602,33 @@ is_gimple_lvalue (tree t) > >>>>> || TREE_CODE (t) == BIT_FIELD_REF); > >>>>> } > >>>>> > >>>>> -/* Return true if T is a GIMPLE condition. */ > >>>>> +/* Helper for is_gimple_condexpr and is_possibly_trapping_gimple_condexpr. */ > >>>>> > >>>>> -bool > >>>>> -is_gimple_condexpr (tree t) > >>>>> +static bool > >>>>> +is_gimple_condexpr_1 (tree t, bool allow_traps) > >>>>> { > >>>>> return (is_gimple_val (t) || (COMPARISON_CLASS_P (t) > >>>>> - && !tree_could_throw_p (t) > >>>>> + && (allow_traps || !tree_could_throw_p (t)) > >>>>> && is_gimple_val (TREE_OPERAND (t, 0)) > >>>>> && is_gimple_val (TREE_OPERAND (t, 1)))); > >>>>> } > >>>>> > >>>>> +/* Return true if T is a GIMPLE condition. */ > >>>>> + > >>>>> +bool > >>>>> +is_gimple_condexpr (tree t) > >>>>> +{ > >>>>> + return is_gimple_condexpr_1 (t, false); > >>>>> +} > >>>>> + > >>>>> +/* Like is_gimple_condexpr, but allow the T to trap. */ > >>>>> + > >>>>> +bool > >>>>> +is_possibly_trapping_gimple_condexpr (tree t) > >>>>> +{ > >>>>> + return is_gimple_condexpr_1 (t, true); > >>>>> +} > >>>>> + > >>>>> /* Return true if T is a gimple address. */ > >>>>> > >>>>> bool > >>>>> diff --git a/gcc/gimple-expr.h b/gcc/gimple-expr.h > >>>>> index 1ad1432bd17..20546ca5b99 100644 > >>>>> --- a/gcc/gimple-expr.h > >>>>> +++ b/gcc/gimple-expr.h > >>>>> @@ -41,6 +41,7 @@ extern void gimple_cond_get_ops_from_tree (tree, enum tree_code *, tree *, > >>>>> tree *); > >>>>> extern bool is_gimple_lvalue (tree); > >>>>> extern bool is_gimple_condexpr (tree); > >>>>> +extern bool is_possibly_trapping_gimple_condexpr (tree); > >>>>> extern bool is_gimple_address (const_tree); > >>>>> extern bool is_gimple_invariant_address (const_tree); > >>>>> extern bool is_gimple_ip_invariant_address (const_tree); > >>>>> diff --git a/gcc/gimplify.c b/gcc/gimplify.c > >>>>> index daa0b71c191..4e6256390c0 100644 > >>>>> --- a/gcc/gimplify.c > >>>>> +++ b/gcc/gimplify.c > >>>>> @@ -12973,6 +12973,7 @@ gimplify_expr (tree *expr_p, gimple_seq *pre_p, gimple_seq *post_p, > >>>>> else if (gimple_test_f == is_gimple_val > >>>>> || gimple_test_f == is_gimple_call_addr > >>>>> || gimple_test_f == is_gimple_condexpr > >>>>> + || gimple_test_f == is_possibly_trapping_gimple_condexpr > >>>>> || gimple_test_f == is_gimple_mem_rhs > >>>>> || gimple_test_f == is_gimple_mem_rhs_or_call > >>>>> || gimple_test_f == is_gimple_reg_rhs > >>>>> @@ -13814,7 +13815,7 @@ gimplify_expr (tree *expr_p, gimple_seq *pre_p, gimple_seq *post_p, > >>>>> enum gimplify_status r0, r1, r2; > >>>>> > >>>>> r0 = gimplify_expr (&TREE_OPERAND (*expr_p, 0), pre_p, > >>>>> - post_p, is_gimple_condexpr, fb_rvalue); > >>>>> + post_p, is_possibly_trapping_gimple_condexpr, fb_rvalue); > >>>>> r1 = gimplify_expr (&TREE_OPERAND (*expr_p, 1), pre_p, > >>>>> post_p, is_gimple_val, fb_rvalue); > >>>>> r2 = gimplify_expr (&TREE_OPERAND (*expr_p, 2), pre_p, > >>>>> diff --git a/gcc/tree-cfg.c b/gcc/tree-cfg.c > >>>>> index b75fdb2e63f..175b858f56b 100644 > >>>>> --- a/gcc/tree-cfg.c > >>>>> +++ b/gcc/tree-cfg.c > >>>>> @@ -4121,8 +4121,11 @@ verify_gimple_assign_ternary (gassign *stmt) > >>>>> return true; > >>>>> } > >>>>> > >>>>> - if (((rhs_code == VEC_COND_EXPR || rhs_code == COND_EXPR) > >>>>> - ? !is_gimple_condexpr (rhs1) : !is_gimple_val (rhs1)) > >>>>> + if ((rhs_code == VEC_COND_EXPR > >>>>> + ? !is_possibly_trapping_gimple_condexpr (rhs1) > >>>>> + : (rhs_code == COND_EXPR > >>>>> + ? !is_gimple_condexpr (rhs1) > >>>>> + : !is_gimple_val (rhs1))) > >>>>> || !is_gimple_val (rhs2) > >>>>> || !is_gimple_val (rhs3)) > >>>>> { > >>>>> > >>>>>> > >>>>>> To go this route you'd have to split the is_gimple_condexpr check > >>>>>> I guess and eventually users turning [VEC_]COND_EXPR into conditional > >>>>>> code (do we have any?) have to be extra careful then. > >>>>>> > >>>>> > >>>>> We have expand_vector_condition, which turns VEC_COND_EXPR into > >>>>> COND_EXPR - but this should be harmless, right? I could not find > >>>>> anything else. > >>>> > >>>> Ugh, I've realized I need to check not only VEC_COND_EXPR, but also > >>>> COND_EXPR usages. There is, of course, a great deal more code, so I'm > >>>> not sure whether I looked exhaustively through it, but there are at > >>>> least store_expr and do_jump which do exactly this during expansion. > >>>> Should we worry about EH edges at this point? > >>> > >>> Well, the EH edge needs to persist (and be rooted off the comparison, > >>> not the selection). > >> > >> Ok, I'm trying to create some samples that may reveal problems with EH > >> edges in these two cases. So far with these experiments I only managed > >> to find and unrelated S/390 bug :-) > >> https://gcc.gnu.org/ml/gcc-patches/2019-09/msg00065.html > >> > >>> That said, I'd simply stop using is_gimple_condexpr for GIMPLE_CONDs > >>> (it allows is_gimple_val which isn't proper form for GIMPLE_COND). Of course > >>> there's code using it for GIMPLE_CONDs which would need to be adjusted. > >> > >> I'm sorry, I don't quite get this - what would that buy us? and what > >> would you use instead? Right now we fix up non-conforming values > >> accepted by is_gimple_val using gimple_cond_get_ops_from_tree - is > >> there a problem with this approach? > >> > >> What I have in mind right now is to: > >> - allow trapping conditions for COND_EXPR and VEC_COND_EXPR; > >> - report them as trapping in operation_could_trap_p and > >> tree_could_trap_p iff their condition is trapping; > >> - find and adjust all places where this messes up EH edges. > >> > >> GIMPLE_COND logic appears to be already covered precisely because it > >> uses is_gimple_condexpr. > >> > >> Am I missing something? > > > > Not really - all I'm saying is that currently we use is_gimple_condexpr > > to check whether a GENERIC tree is suitable for [VEC_]COND_EXPR > > during for example forward propagation. > > > > And GIMPLE_COND already uses its own logic (as you say) but > > still passes use is_gimple_condexpr for it. > > > > So my proposal would be to change is_gimple_condexpr to > > allow trapping [VEC_]COND_EXPR and stop using is_gimple_condexpr > > checks on conditions to be used for GIMPLE_CONDs (and substitute > > another predicate there). For this to work and catch wrong-doings > > we should amend gimple_cond_get_ops_from_tree to assert > > that the extracted condition cannot trap. > > Ah, I think now I understand. While I wanted to keep is_gimple_condexpr > as is and introduce is_possibly_trapping_gimple_condexpr, you're saying > we rather need to change is_gimple_condexpr and introduce, say, > is_non_trapping_gimple_condexpr. > > This makes sense, thanks for the explanation! I'd say is_gimple_cond_expr - bah! stupid clashing names ;) OK, so is_gimple_cond_condexpr vs. is_gimple_condexpr_cond? Hmm, no. I don't like to explicitely spell "non_trapping" here but instead find names that tell one is for GIMPLE_COND while the other is for GIMPLE_ASSIGN with a [VEC_]COND_EXPR operation. Ah, maybe is_gimple_cond_condition () vs. is_gimple_assign_condition ()? Or is_gimple_condexpr_for_cond and is_gimple_condexpr_for_assign? Richard.