VEC_COND_EXPR optimizations v2

Richard Biener richard.guenther@gmail.com
Thu Aug 6 10:29:23 GMT 2020


On Thu, Aug 6, 2020 at 10:17 AM Christophe Lyon
<christophe.lyon@linaro.org> wrote:
>
> Hi,
>
>
> On Wed, 5 Aug 2020 at 16:24, Richard Biener via Gcc-patches
> <gcc-patches@gcc.gnu.org> wrote:
> >
> > On Wed, Aug 5, 2020 at 3:33 PM Marc Glisse <marc.glisse@inria.fr> wrote:
> > >
> > > New version that passed bootstrap+regtest during the night.
> > >
> > > When vector comparisons were forced to use vec_cond_expr, we lost a number of
> > > optimizations (my fault for not adding enough testcases to prevent that).
> > > This patch tries to unwrap vec_cond_expr a bit so some optimizations can
> > > still happen.
> > >
> > > I wasn't planning to add all those transformations together, but adding one
> > > caused a regression, whose fix introduced a second regression, etc.
> > >
> > > Restricting to constant folding would not be sufficient, we also need at
> > > least things like X|0 or X&X. The transformations are quite conservative
> > > with :s and folding only if everything simplifies, we may want to relax
> > > this later. And of course we are going to miss things like a?b:c + a?c:b
> > > -> b+c.
> > >
> > > In terms of number of operations, some transformations turning 2
> > > VEC_COND_EXPR into VEC_COND_EXPR + BIT_IOR_EXPR + BIT_NOT_EXPR might not look
> > > like a gain... I expect the bit_not disappears in most cases, and
> > > VEC_COND_EXPR looks more costly than a simpler BIT_IOR_EXPR.
> > >
> > > I am a bit confused that with avx512 we get types like "vector(4)
> > > <signed-boolean:2>" with :2 and not :1 (is it a hack so true is 1 and not
> > > -1?), but that doesn't matter for this patch.
> >
> > OK.
> >
> > Thanks,
> > Richard.
> >
> > > 2020-08-05  Marc Glisse  <marc.glisse@inria.fr>
> > >
> > >         PR tree-optimization/95906
> > >         PR target/70314
> > >         * match.pd ((c ? a : b) op d, (c ? a : b) op (c ? d : e),
> > >         (v ? w : 0) ? a : b, c1 ? c2 ? a : b : b): New transformations.
> > >         (op (c ? a : b)): Update to match the new transformations.
> > >
> > >         * gcc.dg/tree-ssa/andnot-2.c: New file.
> > >         * gcc.dg/tree-ssa/pr95906.c: Likewise.
> > >         * gcc.target/i386/pr70314.c: Likewise.
> > >
>
> I think this patch is causing several ICEs on arm-none-linux-gnueabihf
> --with-cpu cortex-a9 --with-fpu neon-fp16:
>   Executed from: gcc.c-torture/compile/compile.exp
>     gcc.c-torture/compile/20160205-1.c   -O3 -fomit-frame-pointer
> -funroll-loops -fpeel-loops -ftracer -finline-functions  (internal
> compiler error)
>     gcc.c-torture/compile/20160205-1.c   -O3 -g  (internal compiler error)
>   Executed from: gcc.dg/dg.exp
>     gcc.dg/pr87746.c (internal compiler error)
>   Executed from: gcc.dg/tree-ssa/tree-ssa.exp
>     gcc.dg/tree-ssa/ifc-cd.c (internal compiler error)
>   Executed from: gcc.dg/vect/vect.exp
>     gcc.dg/vect/pr59591-1.c (internal compiler error)
>     gcc.dg/vect/pr59591-1.c -flto -ffat-lto-objects (internal compiler error)
>     gcc.dg/vect/pr86927.c (internal compiler error)
>     gcc.dg/vect/pr86927.c -flto -ffat-lto-objects (internal compiler error)
>     gcc.dg/vect/slp-cond-5.c (internal compiler error)
>     gcc.dg/vect/slp-cond-5.c -flto -ffat-lto-objects (internal compiler error)
>     gcc.dg/vect/vect-23.c (internal compiler error)
>     gcc.dg/vect/vect-23.c -flto -ffat-lto-objects (internal compiler error)
>     gcc.dg/vect/vect-24.c (internal compiler error)
>     gcc.dg/vect/vect-24.c -flto -ffat-lto-objects (internal compiler error)
>     gcc.dg/vect/vect-cond-reduc-6.c (internal compiler error)
>     gcc.dg/vect/vect-cond-reduc-6.c -flto -ffat-lto-objects (internal
> compiler error)
>
> Backtrace for gcc.c-torture/compile/20160205-1.c   -O3
> -fomit-frame-pointer -funroll-loops -fpeel-loops -ftracer
> -finline-functions
> during RTL pass: expand
> /gcc/testsuite/gcc.c-torture/compile/20160205-1.c:2:5: internal
> compiler error: in do_store_flag, at expr.c:12259
> 0x8feb26 do_store_flag
>         /gcc/expr.c:12259
> 0x900201 expand_expr_real_2(separate_ops*, rtx_def*, machine_mode,
> expand_modifier)
>         /gcc/expr.c:9617
> 0x908cd0 expand_expr_real_1(tree_node*, rtx_def*, machine_mode,
> expand_modifier, rtx_def**, bool)
>         /gcc/expr.c:10159
> 0x91174e expand_expr
>         /gcc/expr.h:282
> 0x91174e expand_operands(tree_node*, tree_node*, rtx_def*, rtx_def**,
> rtx_def**, expand_modifier)
>         /gcc/expr.c:8065
> 0x8ff543 expand_expr_real_2(separate_ops*, rtx_def*, machine_mode,
> expand_modifier)
>         /gcc/expr.c:9950
> 0x908cd0 expand_expr_real_1(tree_node*, rtx_def*, machine_mode,
> expand_modifier, rtx_def**, bool)
>         /gcc/expr.c:10159
> 0x91174e expand_expr
>         /gcc/expr.h:282
> 0x91174e expand_operands(tree_node*, tree_node*, rtx_def*, rtx_def**,
> rtx_def**, expand_modifier)
>         /gcc/expr.c:8065
> 0x8ff543 expand_expr_real_2(separate_ops*, rtx_def*, machine_mode,
> expand_modifier)
>         /gcc/expr.c:9950
> 0x908cd0 expand_expr_real_1(tree_node*, rtx_def*, machine_mode,
> expand_modifier, rtx_def**, bool)
>         /gcc/expr.c:10159
> 0x91174e expand_expr
>         /gcc/expr.h:282
> 0x91174e expand_operands(tree_node*, tree_node*, rtx_def*, rtx_def**,
> rtx_def**, expand_modifier)
>         /gcc/expr.c:8065
> 0x8ff543 expand_expr_real_2(separate_ops*, rtx_def*, machine_mode,
> expand_modifier)
>         /gcc/expr.c:9950
> 0x908cd0 expand_expr_real_1(tree_node*, rtx_def*, machine_mode,
> expand_modifier, rtx_def**, bool)
>         /gcc/expr.c:10159
> 0x91174e expand_expr
>         /gcc/expr.h:282
> 0x91174e expand_operands(tree_node*, tree_node*, rtx_def*, rtx_def**,
> rtx_def**, expand_modifier)
>         /gcc/expr.c:8065
> 0x8ff543 expand_expr_real_2(separate_ops*, rtx_def*, machine_mode,
> expand_modifier)
>         /gcc/expr.c:9950
> 0x908cd0 expand_expr_real_1(tree_node*, rtx_def*, machine_mode,
> expand_modifier, rtx_def**, bool)
>         /gcc/expr.c:10159
> 0x91174e expand_expr
>         /gcc/expr.h:282

Hmm, I guess we might need to verify that the VEC_COND_EXPRs
can be RTL expanded, at least if the folding triggers after vector
lowering (but needing to lower a previously expandable VEC_COND_EXPR
would be similarly bad).  So we may need to handle VEC_COND_EXPRs
like VEC_PERMs and thus need to check target support.  Ick.

Richard.

> Christophe
>
>
> > > --
> > > Marc Glisse


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