Message ID | 58acc8c2-b6a4-e9ec-c89b-ad841cf759ed@linux.ibm.com |
---|---|
State | New |
Headers | show |
Series | rs6000: Use NO_EXPR to cast to MMA pointer types | expand |
Hi! On Fri, Sep 02, 2022 at 11:22:07AM -0500, Peter Bergner wrote: > When we cast pointers to our opaque MMA pointers, use NOP_EXPR rather > than VIEW_CONVERT_EXPR. > I think this is just a cleanup and not a correctness thing, so I'm assuming a > backport isn't needed? Or maybe we do to make other potential backports easier? > I'm fine either way. I wouldn't worry about backports. If it does make other backports easier in the future, we can decide to backport this *then*. Okay for trunk. Thanks! (Did you also look at non-MMA VIEW_CONVERT_EXPR uses btw?) Segher
On 9/2/22 11:31 AM, Segher Boessenkool wrote: > I wouldn't worry about backports. If it does make other backports > easier in the future, we can decide to backport this *then*. Ok. > (Did you also look at non-MMA VIEW_CONVERT_EXPR uses btw?) I did. It seemed they were all related to pointers to vectors and I remember you mentioning that as one of the reasons for using VIEW_CONVERT_EXPR over NOP_EXPR, so I left them alone to be safe. > Okay for trunk. Thanks! Ok, pushed to trunk. Thanks! Peter
On Fri, Sep 02, 2022 at 12:02:54PM -0500, Peter Bergner wrote: > On 9/2/22 11:31 AM, Segher Boessenkool wrote: > > (Did you also look at non-MMA VIEW_CONVERT_EXPR uses btw?) > > I did. It seemed they were all related to pointers to vectors and I remember > you mentioning that as one of the reasons for using VIEW_CONVERT_EXPR over > NOP_EXPR, so I left them alone to be safe. Huh? I have no idea what you mean here. Casting from one pointer type to another never needs it. Casting from a scalar integer type to a pointer type not either AFAIKi. But I am not a Gimple expert, all this might be wrong, it isn't documented anywbere :-( Segher
On 9/2/22 12:23 PM, Segher Boessenkool wrote: > On Fri, Sep 02, 2022 at 12:02:54PM -0500, Peter Bergner wrote: >> On 9/2/22 11:31 AM, Segher Boessenkool wrote: >>> (Did you also look at non-MMA VIEW_CONVERT_EXPR uses btw?) >> >> I did. It seemed they were all related to pointers to vectors and I remember >> you mentioning that as one of the reasons for using VIEW_CONVERT_EXPR over >> NOP_EXPR, so I left them alone to be safe. > > Huh? I have no idea what you mean here. > > Casting from one pointer type to another never needs it. Casting from a > scalar integer type to a pointer type not either AFAIKi. But I am not a > Gimple expert, all this might be wrong, it isn't documented anywbere :-( Ah, then I misunderstood you and didn't pick up on the non-pointer thing. ...which just goes to show I'm not an expert and someone else should look at those uses. :-) Peter
On Fri, Sep 2, 2022 at 7:24 PM Segher Boessenkool <segher@kernel.crashing.org> wrote: > > On Fri, Sep 02, 2022 at 12:02:54PM -0500, Peter Bergner wrote: > > On 9/2/22 11:31 AM, Segher Boessenkool wrote: > > > (Did you also look at non-MMA VIEW_CONVERT_EXPR uses btw?) > > > > I did. It seemed they were all related to pointers to vectors and I remember > > you mentioning that as one of the reasons for using VIEW_CONVERT_EXPR over > > NOP_EXPR, so I left them alone to be safe. > > Huh? I have no idea what you mean here. > > Casting from one pointer type to another never needs it. Casting from a > scalar integer type to a pointer type not either AFAIKi. But I am not a > Gimple expert, all this might be wrong, it isn't documented anywbere :-( NOP_EXPR is for conversions between types with the same kind (and pointer-to-integer and integer-to-pointer conversions when pointer and integer are of the same size). When used on vectors it converts the vector elements. When you want to re-interpret V4SI as V4SF you need VIEW_CONVERT_EXPR (bit_cast), likewise V4SI interpreted as V16QI needs that. Think of VIEW_CONVERT as bit_cast and NOP_EXPR as conversion. Of course for some conversions (like unsigned int to int) you can also use a VIEW_CONVERT since it's semantically the same. In those cases we canonicalize to NOP_EXPR via folding. Richard. > > > Segher
On Mon, Sep 05, 2022 at 11:25:21AM +0200, Richard Biener wrote: > On Fri, Sep 2, 2022 at 7:24 PM Segher Boessenkool > <segher@kernel.crashing.org> wrote: > > On Fri, Sep 02, 2022 at 12:02:54PM -0500, Peter Bergner wrote: > > > On 9/2/22 11:31 AM, Segher Boessenkool wrote: > > > > (Did you also look at non-MMA VIEW_CONVERT_EXPR uses btw?) > > > > > > I did. It seemed they were all related to pointers to vectors and I remember > > > you mentioning that as one of the reasons for using VIEW_CONVERT_EXPR over > > > NOP_EXPR, so I left them alone to be safe. > > > > Huh? I have no idea what you mean here. > > > > Casting from one pointer type to another never needs it. Casting from a > > scalar integer type to a pointer type not either AFAIKi. But I am not a > > Gimple expert, all this might be wrong, it isn't documented anywbere :-( > > NOP_EXPR is for conversions between types with the same kind > (and pointer-to-integer and integer-to-pointer > conversions when pointer and integer are of the same size). > When used on vectors it converts the vector elements. When you want to > re-interpret V4SI as V4SF you need VIEW_CONVERT_EXPR (bit_cast), > likewise V4SI interpreted as V16QI needs that. > > Think of VIEW_CONVERT as bit_cast and NOP_EXPR as conversion. > Of course for some conversions (like unsigned int to int) you can also > use a VIEW_CONVERT since it's semantically the same. In those cases > we canonicalize to NOP_EXPR via folding. Thanks for the explanation! About that last point... You say VIEW_CONVERT_EXPR is folded to NOP_EXPR where possible. Does that happen in all cases / can we depend on that? So that in target code like what started this thread the only real difference is documentation of intent? (Which never is unimportant of course!) Segher
> Am 05.09.2022 um 16:53 schrieb Segher Boessenkool <segher@kernel.crashing.org>: > > On Mon, Sep 05, 2022 at 11:25:21AM +0200, Richard Biener wrote: >>> On Fri, Sep 2, 2022 at 7:24 PM Segher Boessenkool >>> <segher@kernel.crashing.org> wrote: >>> On Fri, Sep 02, 2022 at 12:02:54PM -0500, Peter Bergner wrote: >>>> On 9/2/22 11:31 AM, Segher Boessenkool wrote: >>>>> (Did you also look at non-MMA VIEW_CONVERT_EXPR uses btw?) >>>> >>>> I did. It seemed they were all related to pointers to vectors and I remember >>>> you mentioning that as one of the reasons for using VIEW_CONVERT_EXPR over >>>> NOP_EXPR, so I left them alone to be safe. >>> >>> Huh? I have no idea what you mean here. >>> >>> Casting from one pointer type to another never needs it. Casting from a >>> scalar integer type to a pointer type not either AFAIKi. But I am not a >>> Gimple expert, all this might be wrong, it isn't documented anywbere :-( >> >> NOP_EXPR is for conversions between types with the same kind >> (and pointer-to-integer and integer-to-pointer >> conversions when pointer and integer are of the same size). >> When used on vectors it converts the vector elements. When you want to >> re-interpret V4SI as V4SF you need VIEW_CONVERT_EXPR (bit_cast), >> likewise V4SI interpreted as V16QI needs that. >> >> Think of VIEW_CONVERT as bit_cast and NOP_EXPR as conversion. >> Of course for some conversions (like unsigned int to int) you can also >> use a VIEW_CONVERT since it's semantically the same. In those cases >> we canonicalize to NOP_EXPR via folding. > > Thanks for the explanation! > > About that last point... You say VIEW_CONVERT_EXPR is folded to > NOP_EXPR where possible. Does that happen in all cases / can we depend > on that? So that in target code like what started this thread the only > real difference is documentation of intent? (Which never is unimportant > of course!) You should be able to depend on that, yes. Richard > > > Segher
diff --git a/gcc/config/rs6000/rs6000-builtin.cc b/gcc/config/rs6000/rs6000-builtin.cc index e6948b9abb7..0d8be996f4e 100644 --- a/gcc/config/rs6000/rs6000-builtin.cc +++ b/gcc/config/rs6000/rs6000-builtin.cc @@ -1101,7 +1101,7 @@ rs6000_gimple_fold_mma_builtin (gimple_stmt_iterator *gsi, || (fncode == RS6000_BIF_DISASSEMBLE_PAIR_V && TREE_TYPE (TREE_TYPE (dst_ptr)) == vector_pair_type_node)) { - tree dst = build_simple_mem_ref (build1 (VIEW_CONVERT_EXPR, + tree dst = build_simple_mem_ref (build1 (NOP_EXPR, src_type, dst_ptr)); gimplify_assign (dst, src, &new_seq); pop_gimplify_context (NULL); @@ -1125,7 +1125,7 @@ rs6000_gimple_fold_mma_builtin (gimple_stmt_iterator *gsi, = rs6000_builtin_decls[rs6000_builtin_info[fncode].assoc_bif]; tree dst_type = build_pointer_type_for_mode (unsigned_V16QI_type_node, ptr_mode, true); - tree dst_base = build1 (VIEW_CONVERT_EXPR, dst_type, dst_ptr); + tree dst_base = build1 (NOP_EXPR, dst_type, dst_ptr); for (unsigned i = 0; i < nvec; i++) { unsigned index = WORDS_BIG_ENDIAN ? i : nvec - 1 - i; @@ -1151,7 +1151,7 @@ rs6000_gimple_fold_mma_builtin (gimple_stmt_iterator *gsi, tree ptr = gimple_call_arg (stmt, 1); tree lhs = gimple_call_lhs (stmt); if (TREE_TYPE (TREE_TYPE (ptr)) != vector_pair_type_node) - ptr = build1 (VIEW_CONVERT_EXPR, + ptr = build1 (NOP_EXPR, build_pointer_type (vector_pair_type_node), ptr); tree mem = build_simple_mem_ref (build2 (POINTER_PLUS_EXPR, TREE_TYPE (ptr), ptr, offset)); @@ -1168,7 +1168,7 @@ rs6000_gimple_fold_mma_builtin (gimple_stmt_iterator *gsi, tree offset = gimple_call_arg (stmt, 1); tree ptr = gimple_call_arg (stmt, 2); if (TREE_TYPE (TREE_TYPE (ptr)) != vector_pair_type_node) - ptr = build1 (VIEW_CONVERT_EXPR, + ptr = build1 (NOP_EXPR, build_pointer_type (vector_pair_type_node), ptr); tree mem = build_simple_mem_ref (build2 (POINTER_PLUS_EXPR, TREE_TYPE (ptr), ptr, offset));