Patchwork [4.8,i386] : Enable post-reload compare optimization pass (PR28685)

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Submitter Uros Bizjak
Date Feb. 7, 2012, 10 a.m.
Message ID <CAFULd4Y+DHEBCXXgoEAx4XR=B-1-nUpDYe=Pp_jjZyscKZsp4A@mail.gmail.com>
Download mbox | patch
Permalink /patch/139894/
State New
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Comments

Uros Bizjak - Feb. 7, 2012, 10 a.m.
On Mon, Feb 6, 2012 at 10:30 PM, Uros Bizjak <ubizjak@gmail.com> wrote:

>> Hmm.  Well, the only thing that's going to work for x86 is the double-compare
>> elimination portion.
>>
>> If we want to use this pass for x86, then for 4.8 we should also fix the
>> discrepancy between the compare-elim canonical
>>
>>  [(operate)
>>   (set-cc)]
>>
>> and the combine canonical
>>
>>  [(set-cc)
>>   (operate)]
>>
>> (Because of the simplicity of the substitution in compare-elim, I prefer
>> the former as the canonical canonical.)
>
> You are probably referring to following testcase:
>
> --cut here--
> int test (int a, int b)
> {
>  int lt = a + b < 0;
>  int eq = a + b == 0;
>  if (lt)
>    return 1;
>  return eq;
> }
> --cut here--
>
> where combine creates:
>
> Trying 8 -> 9:
> Successfully matched this instruction:
> (parallel [
>        (set (reg:CCZ 17 flags)
>            (compare:CCZ (plus:SI (reg/v:SI 63 [ a ])
>                    (reg/v:SI 64 [ b ]))
>                (const_int 0 [0])))
>        (set (reg:SI 60 [ D.1710 ])
>            (plus:SI (reg/v:SI 63 [ a ])
>                (reg/v:SI 64 [ b ])))
>    ])

Attached patch teaches combine to swap operands of a double set
pattern and retries recognition. Also added are minimum
target-dependant changes to handle the testcase above.

Unfortunately, compare elimination was not able to remove redundant
compare, although the testcase is carefully crafted to require only
sign flag to be valid. Following enters compare-elim pass:

(insn 9 8 10 2 (parallel [
            (set (reg:SI 5 di [orig:60 D.1710 ] [60])
                (plus:SI (reg/v:SI 5 di [orig:63 a ] [63])
                    (reg/v:SI 4 si [orig:64 b ] [64])))
            (set (reg:CCZ 17 flags)
                (compare:CCZ (plus:SI (reg/v:SI 5 di [orig:63 a ] [63])
                        (reg/v:SI 4 si [orig:64 b ] [64]))
                    (const_int 0 [0])))
        ]) cmp.c:4 261 {*addsi_2}
     (nil))

(note 10 9 33 2 NOTE_INSN_DELETED)

(insn 33 10 34 2 (set (reg:QI 1 dx [65])
        (eq:QI (reg:CCZ 17 flags)
            (const_int 0 [0]))) cmp.c:4 595 {*setcc_qi}
     (nil))

(insn 34 33 30 2 (set (reg:SI 1 dx [65])
        (zero_extend:SI (reg:QI 1 dx [65]))) cmp.c:4 123
{*zero_extendqisi2_movzbl}
     (nil))

(insn 30 34 29 2 (set (reg/v:SI 0 ax [orig:59 eq ] [59])
        (const_int 1 [0x1])) cmp.c:6 64 {*movsi_internal}
     (expr_list:REG_EQUAL (const_int 1 [0x1])
        (nil)))

(insn 29 30 31 2 (set (reg:CCGOC 17 flags)
        (compare:CCGOC (reg:SI 5 di [orig:60 D.1710 ] [60])
            (const_int 0 [0]))) cmp.c:6 2 {*cmpsi_ccno_1}
     (nil))

(insn 31 29 25 2 (set (reg/v:SI 0 ax [orig:59 eq ] [59])
        (if_then_else:SI (ge (reg:CCGOC 17 flags)
                (const_int 0 [0]))
            (reg:SI 1 dx [65])
            (reg/v:SI 0 ax [orig:59 eq ] [59]))) cmp.c:6 903 {*movsicc_noc}
     (nil))

The resulting code still includes redundant test that sets sign flag:

test:
        addl    %esi, %edi
        movl    $1, %eax
        sete    %dl
 >>   testl   %edi, %edi
        movzbl  %dl, %edx
        cmovns  %edx, %eax
        ret

(BTW: I think that the change to combine.c would be nice to have, to
find more other combine opportunities. I will propose the patch
separately.)

Uros.
Richard Guenther - Feb. 7, 2012, 10:04 a.m.
On Tue, Feb 7, 2012 at 11:00 AM, Uros Bizjak <ubizjak@gmail.com> wrote:
> On Mon, Feb 6, 2012 at 10:30 PM, Uros Bizjak <ubizjak@gmail.com> wrote:
>
>>> Hmm.  Well, the only thing that's going to work for x86 is the double-compare
>>> elimination portion.
>>>
>>> If we want to use this pass for x86, then for 4.8 we should also fix the
>>> discrepancy between the compare-elim canonical
>>>
>>>  [(operate)
>>>   (set-cc)]
>>>
>>> and the combine canonical
>>>
>>>  [(set-cc)
>>>   (operate)]
>>>
>>> (Because of the simplicity of the substitution in compare-elim, I prefer
>>> the former as the canonical canonical.)
>>
>> You are probably referring to following testcase:
>>
>> --cut here--
>> int test (int a, int b)
>> {
>>  int lt = a + b < 0;
>>  int eq = a + b == 0;
>>  if (lt)
>>    return 1;
>>  return eq;
>> }
>> --cut here--
>>
>> where combine creates:
>>
>> Trying 8 -> 9:
>> Successfully matched this instruction:
>> (parallel [
>>        (set (reg:CCZ 17 flags)
>>            (compare:CCZ (plus:SI (reg/v:SI 63 [ a ])
>>                    (reg/v:SI 64 [ b ]))
>>                (const_int 0 [0])))
>>        (set (reg:SI 60 [ D.1710 ])
>>            (plus:SI (reg/v:SI 63 [ a ])
>>                (reg/v:SI 64 [ b ])))
>>    ])
>
> Attached patch teaches combine to swap operands of a double set
> pattern and retries recognition. Also added are minimum
> target-dependant changes to handle the testcase above.
>
> Unfortunately, compare elimination was not able to remove redundant
> compare, although the testcase is carefully crafted to require only
> sign flag to be valid. Following enters compare-elim pass:
>
> (insn 9 8 10 2 (parallel [
>            (set (reg:SI 5 di [orig:60 D.1710 ] [60])
>                (plus:SI (reg/v:SI 5 di [orig:63 a ] [63])
>                    (reg/v:SI 4 si [orig:64 b ] [64])))
>            (set (reg:CCZ 17 flags)
>                (compare:CCZ (plus:SI (reg/v:SI 5 di [orig:63 a ] [63])
>                        (reg/v:SI 4 si [orig:64 b ] [64]))
>                    (const_int 0 [0])))
>        ]) cmp.c:4 261 {*addsi_2}
>     (nil))
>
> (note 10 9 33 2 NOTE_INSN_DELETED)
>
> (insn 33 10 34 2 (set (reg:QI 1 dx [65])
>        (eq:QI (reg:CCZ 17 flags)
>            (const_int 0 [0]))) cmp.c:4 595 {*setcc_qi}
>     (nil))
>
> (insn 34 33 30 2 (set (reg:SI 1 dx [65])
>        (zero_extend:SI (reg:QI 1 dx [65]))) cmp.c:4 123
> {*zero_extendqisi2_movzbl}
>     (nil))
>
> (insn 30 34 29 2 (set (reg/v:SI 0 ax [orig:59 eq ] [59])
>        (const_int 1 [0x1])) cmp.c:6 64 {*movsi_internal}
>     (expr_list:REG_EQUAL (const_int 1 [0x1])
>        (nil)))
>
> (insn 29 30 31 2 (set (reg:CCGOC 17 flags)
>        (compare:CCGOC (reg:SI 5 di [orig:60 D.1710 ] [60])
>            (const_int 0 [0]))) cmp.c:6 2 {*cmpsi_ccno_1}
>     (nil))
>
> (insn 31 29 25 2 (set (reg/v:SI 0 ax [orig:59 eq ] [59])
>        (if_then_else:SI (ge (reg:CCGOC 17 flags)
>                (const_int 0 [0]))
>            (reg:SI 1 dx [65])
>            (reg/v:SI 0 ax [orig:59 eq ] [59]))) cmp.c:6 903 {*movsicc_noc}
>     (nil))
>
> The resulting code still includes redundant test that sets sign flag:
>
> test:
>        addl    %esi, %edi
>        movl    $1, %eax
>        sete    %dl
>  >>   testl   %edi, %edi
>        movzbl  %dl, %edx
>        cmovns  %edx, %eax
>        ret
>
> (BTW: I think that the change to combine.c would be nice to have, to
> find more other combine opportunities. I will propose the patch
> separately.)

Shouldn't there be a canonical order for parallels throughout the whole
compiler?  Maybe just enforced by gen_rtx_PARALLEL / RTL checking?
At least as far as I understand "execution order" of insns inside a PARALLEL
is undefined.

Richard.

> Uros.
Uros Bizjak - Feb. 7, 2012, 10:46 a.m.
On Tue, Feb 7, 2012 at 11:04 AM, Richard Guenther
<richard.guenther@gmail.com> wrote:

>> (BTW: I think that the change to combine.c would be nice to have, to
>> find more other combine opportunities. I will propose the patch
>> separately.)
>
> Shouldn't there be a canonical order for parallels throughout the whole
> compiler?  Maybe just enforced by gen_rtx_PARALLEL / RTL checking?
> At least as far as I understand "execution order" of insns inside a PARALLEL
> is undefined.

All operations inside parallel happen "at the same time". And there is
no canonical order enforced, as sadly shown by the discrepancy between
combine and compare elimination passes.

Uros.
Richard Guenther - Feb. 7, 2012, 10:48 a.m.
On Tue, Feb 7, 2012 at 11:46 AM, Uros Bizjak <ubizjak@gmail.com> wrote:
> On Tue, Feb 7, 2012 at 11:04 AM, Richard Guenther
> <richard.guenther@gmail.com> wrote:
>
>>> (BTW: I think that the change to combine.c would be nice to have, to
>>> find more other combine opportunities. I will propose the patch
>>> separately.)
>>
>> Shouldn't there be a canonical order for parallels throughout the whole
>> compiler?  Maybe just enforced by gen_rtx_PARALLEL / RTL checking?
>> At least as far as I understand "execution order" of insns inside a PARALLEL
>> is undefined.
>
> All operations inside parallel happen "at the same time". And there is
> no canonical order enforced, as sadly shown by the discrepancy between
> combine and compare elimination passes.

Sure - all what I say is that the fix should be to enforce such canonical
order instead of dealing with both.

Richard.

> Uros.
Uros Bizjak - Feb. 7, 2012, 10:55 a.m.
On Tue, Feb 7, 2012 at 11:48 AM, Richard Guenther
<richard.guenther@gmail.com> wrote:

>>>> (BTW: I think that the change to combine.c would be nice to have, to
>>>> find more other combine opportunities. I will propose the patch
>>>> separately.)
>>>
>>> Shouldn't there be a canonical order for parallels throughout the whole
>>> compiler?  Maybe just enforced by gen_rtx_PARALLEL / RTL checking?
>>> At least as far as I understand "execution order" of insns inside a PARALLEL
>>> is undefined.
>>
>> All operations inside parallel happen "at the same time". And there is
>> no canonical order enforced, as sadly shown by the discrepancy between
>> combine and compare elimination passes.
>
> Sure - all what I say is that the fix should be to enforce such canonical
> order instead of dealing with both.

rth proposed to adopt new scheme to change combine.c. However, I don't
think this is a good idea, since it would mean "fixing" many existing
in-tree and out-of-tree targets. OTOH, I thought that swapping
operands in combine would also benefit other parts of the compiler,
namely load/store multiple patterns, maybe swap insns, and similar.

It was also fairly easy to teach combine to handle both approaches. ;)

Uros.
Uros Bizjak - Feb. 7, 2012, 6:50 p.m.
On Tue, Feb 7, 2012 at 11:00 AM, Uros Bizjak <ubizjak@gmail.com> wrote:

>>> Hmm.  Well, the only thing that's going to work for x86 is the double-compare
>>> elimination portion.
>>>
>>> If we want to use this pass for x86, then for 4.8 we should also fix the
>>> discrepancy between the compare-elim canonical
>>>
>>>  [(operate)
>>>   (set-cc)]
>>>
>>> and the combine canonical
>>>
>>>  [(set-cc)
>>>   (operate)]
>>>
>>> (Because of the simplicity of the substitution in compare-elim, I prefer
>>> the former as the canonical canonical.)
>>
>> You are probably referring to following testcase:
>>
>> --cut here--
>> int test (int a, int b)
>> {
>>  int lt = a + b < 0;
>>  int eq = a + b == 0;
>>  if (lt)
>>    return 1;
>>  return eq;
>> }
>> --cut here--
>>
>> where combine creates:
>>
>> Trying 8 -> 9:
>> Successfully matched this instruction:
>> (parallel [
>>        (set (reg:CCZ 17 flags)
>>            (compare:CCZ (plus:SI (reg/v:SI 63 [ a ])
>>                    (reg/v:SI 64 [ b ]))
>>                (const_int 0 [0])))
>>        (set (reg:SI 60 [ D.1710 ])
>>            (plus:SI (reg/v:SI 63 [ a ])
>>                (reg/v:SI 64 [ b ])))
>>    ])
>
> Attached patch teaches combine to swap operands of a double set
> pattern and retries recognition. Also added are minimum
> target-dependant changes to handle the testcase above.

Please ignore this idea. I am preparing target-only patchset that
moves x86 entirely to post-reload flags handling (similar to rx and
mn10300 targets). Not a 4.7 material in any way.

Uros.

Patch

Index: combine.c
===================================================================
--- combine.c	(revision 183953)
+++ combine.c	(working copy)
@@ -10687,6 +10687,30 @@  recog_for_combine (rtx *pnewpat, rtx insn, rtx *pn
       print_rtl_single (dump_file, pat);
     }
 
+  /* If PAT is a PARALLEL with two SETs, swap the SETs and try again.  */
+  if (insn_code_number < 0
+      && GET_CODE (pat) == PARALLEL
+      && XVECLEN (pat, 0) == 2
+      && GET_CODE (XVECEXP (pat, 0, 0)) == SET
+      && GET_CODE (XVECEXP (pat, 0, 1)) == SET)
+    {
+      rtx set0 = XVECEXP (pat, 0, 0);
+      rtx set1 = XVECEXP (pat, 0, 1);
+
+      SUBST (XVECEXP (pat, 0, 0), set1);
+      SUBST (XVECEXP (pat, 0, 1), set0);
+
+      insn_code_number = recog (pat, insn, &num_clobbers_to_add);
+      if (dump_file && (dump_flags & TDF_DETAILS))
+	{
+	  if (insn_code_number < 0)
+	    fputs ("Failed to match this instruction:\n", dump_file);
+	  else
+	    fputs ("Successfully matched this instruction:\n", dump_file);
+	  print_rtl_single (dump_file, pat);
+	}
+    }
+
   /* If it isn't, there is the possibility that we previously had an insn
      that clobbered some register as a side effect, but the combined
      insn doesn't need to do that.  So try once more without the clobbers
Index: config/i386/i386.md
===================================================================
--- config/i386/i386.md	(revision 183953)
+++ config/i386/i386.md	(working copy)
@@ -5808,14 +5808,14 @@ 
 	(zero_extend:DI (plus:SI (match_dup 1) (match_dup 2))))])
 
 (define_insn "*add<mode>_2"
-  [(set (reg FLAGS_REG)
+  [(set (match_operand:SWI 0 "nonimmediate_operand" "=<r>,<r>m")
+	(plus:SWI
+	  (match_operand:SWI 1 "nonimmediate_operand" "%0,0")
+	  (match_operand:SWI 2 "<general_operand>" "<g>,<r><i>")))
+   (set (reg FLAGS_REG)
 	(compare
-	  (plus:SWI
-	    (match_operand:SWI 1 "nonimmediate_operand" "%0,0")
-	    (match_operand:SWI 2 "<general_operand>" "<g>,<r><i>"))
-	  (const_int 0)))
-   (set (match_operand:SWI 0 "nonimmediate_operand" "=<r>,<r>m")
-	(plus:SWI (match_dup 1) (match_dup 2)))]
+	  (plus:SWI (match_dup 1) (match_dup 2))
+	  (const_int 0)))]
   "ix86_match_ccmode (insn, CCGOCmode)
    && ix86_binary_operator_ok (PLUS, <MODE>mode, operands)"
 {
Index: config/i386/i386.c
===================================================================
--- config/i386/i386.c	(revision 183953)
+++ config/i386/i386.c	(working copy)
@@ -17611,7 +17611,7 @@  ix86_match_ccmode (rtx insn, enum machine_mode req
 
   set = PATTERN (insn);
   if (GET_CODE (set) == PARALLEL)
-    set = XVECEXP (set, 0, 0);
+    set = XVECEXP (set, 0, 1);
   gcc_assert (GET_CODE (set) == SET);
   gcc_assert (GET_CODE (SET_SRC (set)) == COMPARE);
 
@@ -38685,6 +38685,9 @@  ix86_autovectorize_vector_sizes (void)
 #undef TARGET_EXPAND_TO_RTL_HOOK
 #define TARGET_EXPAND_TO_RTL_HOOK ix86_maybe_switch_abi
 
+#undef TARGET_FLAGS_REGNUM
+#define TARGET_FLAGS_REGNUM FLAGS_REG
+
 #undef TARGET_LEGITIMATE_ADDRESS_P
 #define TARGET_LEGITIMATE_ADDRESS_P ix86_legitimate_address_p