Re: [PATCH] middle-end/126788 - more vector folding

On Thu, Aug 13, 2026 at 9:09 PM Richard Biener <[email protected]> wrote:
>
> The last match.pd update for double-conversion folding didn't handle
> the case where a vector conversion would go away because
> supportable_convert_operation doesn't consider a noop conversion
> (or a sign conversion).  The following rectifies this, allowing
> a NOP_EXPR and VIEW_CONVERT_EXPR for same mode types as supportable
> conversion as we can RTL expand that just fine.
>
> Bootstrap and regtest running on x86_64-unknown-linux-gnu.
>
> I'll note that the .VEC_CONVERT IFNs from initial __builtin_convertvector
> lowering survive unfolded until the veclower pass where, if the
> conversions are not supported, they will be open-coded and not
> folded either.  I wonder why we chose to expand to .VEC_CONVERT
> instead of using FLOAT_EXPR/FIX_TRUNC_EXPR/NOP_EXPR as appropriate
> and lower those if not supported?  At least I don't look forward to
> add .VEC_CONVERT support to all conversion foldings?
>
> I'll also note that the guards I put in place when adding
> vector integer support to double-conversion folding will now
> pessimize the case where neither (one of?) the former nor the
> new conversion would be supported because of the type not
> having vector mode.
>
>         PR middle-end/126788
>         * optabs-tree.cc (supportable_convert_operation): For same
>         modes allow NOP_EXPR and VIEW_CONVERT_EXPR.
>
>         * gcc.target/i386/pr126788.c: New testcase.
> ---
>  gcc/optabs-tree.cc                       |  4 ++++
>  gcc/testsuite/gcc.target/i386/pr126788.c | 24 ++++++++++++++++++++++++
>  2 files changed, 28 insertions(+)
>  create mode 100644 gcc/testsuite/gcc.target/i386/pr126788.c
>
> diff --git a/gcc/optabs-tree.cc b/gcc/optabs-tree.cc
> index 5fbdcd3a730..5360a509f8d 100644
> --- a/gcc/optabs-tree.cc
> +++ b/gcc/optabs-tree.cc
> @@ -375,6 +375,10 @@ supportable_convert_operation (enum tree_code code,
>    if (!VECTOR_MODE_P (m1) || !VECTOR_MODE_P (m2))
>      return false;
>
> +  if (m1 == m2
> +      && (CONVERT_EXPR_CODE_P (code) || code == VIEW_CONVERT_EXPR))
> +    return true;
> +
>    /* First check if we can done conversion directly.  */
>    if ((code == FIX_TRUNC_EXPR
>         && can_fix_p (m1,m2,TYPE_UNSIGNED (vectype_out), &truncp)
> diff --git a/gcc/testsuite/gcc.target/i386/pr126788.c b/gcc/testsuite/gcc.target/i386/pr126788.c
> new file mode 100644
> index 00000000000..0448284e8f6
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/i386/pr126788.c
> @@ -0,0 +1,24 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O -msse2" } */
> +
> +typedef int  v2si __attribute__((vector_size (8)));
> +typedef unsigned int  v2usi __attribute__((vector_size (8)));
> +typedef long long v2di __attribute__((vector_size (16)));
> +
> +v2si
> +f1 (v2si a, v2si b)
> +{
> +
> +  v2di z = __builtin_convertvector (a, v2di);
> +  return __builtin_convertvector (z, v2si);
> +}
> +
> +v2usi
> +f2 (v2si a, v2si b)
> +{
> +
> +  v2di z = __builtin_convertvector (a, v2di);
> +  return __builtin_convertvector (z, v2usi);
> +}
> +
> +/* { dg-final { scan-assembler-not "xmm" { target { ! ia32 } } } } */
> --

I think this may cause:

FAIL: gcc.dg/bitint-98.c 1 blank line(s) in output
FAIL: gcc.dg/bitint-98.c 1 blank line(s) in output
FAIL: gcc.dg/bitint-98.c (internal compiler error: verify_gimple failed)
FAIL: gcc.dg/bitint-98.c (internal compiler error: verify_gimple failed)
FAIL: gcc.dg/bitint-98.c (test for excess errors)
FAIL: gcc.dg/bitint-98.c (test for excess errors)
FAIL: gcc.dg/torture/bitint-16.c   -O2   2 blank line(s) in output
FAIL: gcc.dg/torture/bitint-16.c   -O2   2 blank line(s) in output
FAIL: gcc.dg/torture/bitint-16.c   -O2  (internal compiler error:
verify_gimple failed)
FAIL: gcc.dg/torture/bitint-16.c   -O2  (internal compiler error:
verify_gimple failed)
FAIL: gcc.dg/torture/bitint-16.c   -O2  (test for excess errors)
FAIL: gcc.dg/torture/bitint-16.c   -O2  (test for excess errors)
FAIL: gcc.dg/vect/vect-over-widen-23.c -flto -ffat-lto-objects
scan-tree-dump vect "VIEW_CONVERT_EXPR<vector[^ ]* unsigned"
FAIL: gcc.dg/vect/vect-over-widen-23.c -flto -ffat-lto-objects
scan-tree-dump vect "VIEW_CONVERT_EXPR<vector[^ ]* unsigned"
FAIL: gcc.dg/vect/vect-over-widen-23.c scan-tree-dump vect
"VIEW_CONVERT_EXPR<vector[^ ]* unsigned"
FAIL: gcc.dg/vect/vect-over-widen-23.c scan-tree-dump vect
"VIEW_CONVERT_EXPR<vector[^ ]* unsigned"
FAIL: gcc.target/i386/avx512f-pr114157.c 1 blank line(s) in output
FAIL: gcc.target/i386/avx512f-pr114157.c 1 blank line(s) in output
FAIL: gcc.target/i386/avx512f-pr114157.c (internal compiler error:
verify_gimple failed)
FAIL: gcc.target/i386/avx512f-pr114157.c (internal compiler error:
verify_gimple failed)
FAIL: gcc.target/i386/avx512f-pr114157.c (test for excess errors)
FAIL: gcc.target/i386/avx512f-pr114157.c (test for excess errors)
FAIL: gcc.target/i386/cond_op_addsubmul_d-1.c scan-tree-dump optimized
".COND_ADD"
FAIL: gcc.target/i386/cond_op_addsubmul_d-1.c scan-tree-dump optimized
".COND_ADD"
FAIL: gcc.target/i386/cond_op_addsubmul_d-1.c scan-tree-dump optimized
".COND_MUL"
FAIL: gcc.target/i386/cond_op_addsubmul_d-1.c scan-tree-dump optimized
".COND_MUL"
FAIL: gcc.target/i386/cond_op_addsubmul_d-1.c scan-tree-dump optimized
".COND_SUB"
FAIL: gcc.target/i386/cond_op_addsubmul_d-1.c scan-tree-dump optimized
".COND_SUB"
FAIL: gcc.target/i386/cond_op_addsubmul_q-1.c scan-tree-dump optimized
".COND_ADD"
FAIL: gcc.target/i386/cond_op_addsubmul_q-1.c scan-tree-dump optimized
".COND_MUL"
FAIL: gcc.target/i386/cond_op_addsubmul_q-1.c scan-tree-dump optimized
".COND_SUB"
FAIL: gcc.target/i386/cond_op_addsubmul_w-1.c scan-tree-dump optimized
".COND_ADD"
FAIL: gcc.target/i386/cond_op_addsubmul_w-1.c scan-tree-dump optimized
".COND_ADD"
FAIL: gcc.target/i386/cond_op_addsubmul_w-1.c scan-tree-dump optimized
".COND_MUL"
FAIL: gcc.target/i386/cond_op_addsubmul_w-1.c scan-tree-dump optimized
".COND_MUL"
FAIL: gcc.target/i386/cond_op_addsubmul_w-1.c scan-tree-dump optimized
".COND_SUB"
FAIL: gcc.target/i386/cond_op_addsubmul_w-1.c scan-tree-dump optimized
".COND_SUB"
FAIL: gfortran.dg/bind-c-contiguous-3.f90   -O3 -fomit-frame-pointer
-funroll-loops -fpeel-loops -ftracer -finline-functions  (internal
compiler error: verify_gimple failed)
FAIL: gfortran.dg/bind-c-contiguous-3.f90   -O3 -fomit-frame-pointer
-funroll-loops -fpeel-loops -ftracer -finline-functions  (test for
excess errors)
FAIL: gfortran.dg/intrinsic_ifunction_1.f90   -O3 -fomit-frame-pointer
-funroll-loops -fpeel-loops -ftracer -finline-functions  (internal
compiler error: verify_gimple failed)
FAIL: gfortran.dg/intrinsic_ifunction_1.f90   -O3 -fomit-frame-pointer
-funroll-loops -fpeel-loops -ftracer -finline-functions  (test for
excess errors)

with

$ make check RUNTESTFLAGS="--target_board='unix{-m32\ -march=x86-64-v4}'"

-- 
H.J.