On Sun, Nov 16, 2025 at 1:52 PM Robin Dapp <[email protected]> wrote:
>
> Hi,
>
> I observed a vect-construct forwprop opportunity in x264 that we
> could handle when checking for a nop conversion instead of a useless
> conversion. IMHO a nop-conversion check is sufficient as we're only
> dealing with permutations in simplify_vector_constructor.
>
> This patch replaces uses of useless_type_conversion_p with
> tree_nop_conversion_p in simplify_vector_constructor.
>
> It was bootstrapped and regtested on x86 and power10, regtested on
> riscv64, aarch64 still running.
>
> There is a single scan-test failure on power
> (gcc.target/powerpc/builtins-1.c) but it doesn't look
> like a dealbreaker. I have yet to check it in more detail, though.
My only suggestion is to add a (more generic) testcase like
gcc.dg/tree-ssa/forwprop-43.c or gcc.dg/tree-ssa/forwprop-35.c .
Thanks,
Andrew
>
> Regards
> Robin
>
> gcc/ChangeLog:
>
> * tree-ssa-forwprop.cc (simplify_vector_constructor):
> Allow nop conversions.
>
> gcc/testsuite/ChangeLog:
>
> * gcc.target/riscv/rvv/autovec/pr118019-3.c: New test.
> ---
> .../gcc.target/riscv/rvv/autovec/pr118019-3.c | 51 +++++++++++++++++++
> gcc/tree-ssa-forwprop.cc | 16 +++---
> 2 files changed, 59 insertions(+), 8 deletions(-)
> create mode 100644 gcc/testsuite/gcc.target/riscv/rvv/autovec/pr118019-3.c
>
> diff --git a/gcc/testsuite/gcc.target/riscv/rvv/autovec/pr118019-3.c
> b/gcc/testsuite/gcc.target/riscv/rvv/autovec/pr118019-3.c
> new file mode 100644
> index 00000000000..6cb761f63c0
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/riscv/rvv/autovec/pr118019-3.c
> @@ -0,0 +1,51 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O3 -march=rv64gcv_zvl512b -mabi=lp64d
> -mno-vector-strict-align -mmax-vectorization -fdump-tree-optimized" } */
> +
> +/* Ensure we don't use a vector constructor but a permute. */
> +
> +typedef unsigned char uint8_t;
> +typedef unsigned short uint16_t;
> +typedef unsigned int uint32_t;
> +
> +#define HADAMARD4(d0, d1, d2, d3, s0, s1, s2, s3) {\
> + int t0 = s0 + s1;\
> + int t1 = s0 - s1;\
> + int t2 = s2 + s3;\
> + int t3 = s2 - s3;\
> + d0 = t0 + t2;\
> + d2 = t0 - t2;\
> + d1 = t1 + t3;\
> + d3 = t1 - t3;\
> +}
> +
> +uint32_t
> +abs2 (uint32_t a)
> +{
> + uint32_t s = ((a >> 15) & 0x10001) * 0xffff;
> + return (a + s) ^ s;
> +}
> +
> +int
> +x264_pixel_satd_8x4 (uint8_t *pix1, int i_pix1, uint8_t *pix2, int i_pix2)
> +{
> + uint32_t tmp[4][4];
> + uint32_t a0, a1, a2, a3;
> + int sum = 0;
> + for (int i = 0; i < 4; i++, pix1 += i_pix1, pix2 += i_pix2)
> + {
> + a0 = (pix1[0] - pix2[0]) + ((pix1[4] - pix2[4]) << 16);
> + a1 = (pix1[1] - pix2[1]) + ((pix1[5] - pix2[5]) << 16);
> + a2 = (pix1[2] - pix2[2]) + ((pix1[6] - pix2[6]) << 16);
> + a3 = (pix1[3] - pix2[3]) + ((pix1[7] - pix2[7]) << 16);
> + HADAMARD4 (tmp[i][0], tmp[i][1], tmp[i][2], tmp[i][3], a0, a1, a2, a3);
> + }
> +#pragma GCC unroll 4
> + for (int i = 0; i < 4; i++)
> + {
> + HADAMARD4 (a0, a1, a2, a3, tmp[0][i], tmp[1][i], tmp[2][i], tmp[3][i]);
> + sum += abs2 (a0) + abs2 (a1) + abs2 (a2) + abs2 (a3);
> + }
> + return (((uint16_t) sum) + ((uint32_t) sum >> 16)) >> 1;
> +}
> +
> +/* { dg-final { scan-tree-dump-not "BIT_FIELD_REF" "optimized" } } */
> diff --git a/gcc/tree-ssa-forwprop.cc b/gcc/tree-ssa-forwprop.cc
> index 9f8d4ad3b44..5dbcdd7b4bd 100644
> --- a/gcc/tree-ssa-forwprop.cc
> +++ b/gcc/tree-ssa-forwprop.cc
> @@ -3827,11 +3827,11 @@ simplify_vector_constructor (gimple_stmt_iterator
> *gsi)
> if (op1
> && TREE_CODE ((ref = TREE_OPERAND (op1, 0))) == SSA_NAME
> && VECTOR_TYPE_P (TREE_TYPE (ref))
> - && (useless_type_conversion_p (TREE_TYPE (op1),
> - TREE_TYPE (TREE_TYPE (ref)))
> + && (tree_nop_conversion_p (TREE_TYPE (op1),
> + TREE_TYPE (TREE_TYPE (ref)))
> || (VECTOR_TYPE_P (TREE_TYPE (op1))
> - && useless_type_conversion_p (TREE_TYPE (TREE_TYPE (op1)),
> - TREE_TYPE (TREE_TYPE (ref)))
> + && tree_nop_conversion_p (TREE_TYPE (TREE_TYPE (op1)),
> + TREE_TYPE (TREE_TYPE (ref)))
> && TYPE_VECTOR_SUBPARTS (TREE_TYPE (op1))
> .is_constant (&nsubelts)))
> && constant_multiple_p (bit_field_size (op1), nsubelts,
> @@ -4055,8 +4055,8 @@ simplify_vector_constructor (gimple_stmt_iterator *gsi)
> {
> gcc_assert (known_eq (TYPE_VECTOR_SUBPARTS (type),
> TYPE_VECTOR_SUBPARTS (src_type))
> - && useless_type_conversion_p (TREE_TYPE (type),
> - TREE_TYPE
> (src_type)));
> + && tree_nop_conversion_p (TREE_TYPE (type),
> + TREE_TYPE (src_type)));
> tree rhs = build1 (VIEW_CONVERT_EXPR, type, orig[0]);
> orig[0] = make_ssa_name (type);
> gassign *assign = gimple_build_assign (orig[0], rhs);
> @@ -4192,8 +4192,8 @@ simplify_vector_constructor (gimple_stmt_iterator *gsi)
> {
> gcc_assert (known_eq (TYPE_VECTOR_SUBPARTS (type),
> TYPE_VECTOR_SUBPARTS (perm_type))
> - && useless_type_conversion_p (TREE_TYPE (type),
> - TREE_TYPE (perm_type)));
> + && tree_nop_conversion_p (TREE_TYPE (type),
> + TREE_TYPE (perm_type)));
> res = gimple_build (&stmts, VIEW_CONVERT_EXPR, type, res);
> }
> /* Blend in the actual constant. */
> --
> 2.51.0
>
