On Tue, Dec 16, 2025 at 11:59 AM Robin Dapp <[email protected]> wrote:
>
> Hi,
>
> When using pack or unpack in the simplification of a vector constructor
> we must make sure that the original BIT_FIELD_REF was no sign-changing
> nop conversion. If it was we cannot safely pack/unpack as that would
> skip sign or zero extensions. This patch adds useless_type_conversion_p
> to both paths.
>
> Bootstrapped and regtested on x86 and power10. On power10 I surprisingly
> saw one algol68 failure with the patch but that can only be unrelated and due
> to the build environment. Re-testing in progress.
>
> Regtested on riscv64 and aarch64, and loongarch64 via qemu.
>
> I tried coming up with an x86 test case but failed. Suggestions welcome.
OK.
Richard.
> Regards
> Robin
>
> PR tree-optimization/123117
>
> gcc/ChangeLog:
>
> * tree-ssa-forwprop.cc (simplify_vector_constructor):
> Check if we had a nop conversion and don't use pack/unpack in
> that case.
>
> gcc/testsuite/ChangeLog:
>
> * gcc.target/loongarch/vector/lsx/pr123117.c: New test.
> ---
> .../gcc.target/loongarch/vector/lsx/pr123117.c | 17 +++++++++++++++++
> gcc/tree-ssa-forwprop.cc | 12 ++++++++++++
> 2 files changed, 29 insertions(+)
> create mode 100644 gcc/testsuite/gcc.target/loongarch/vector/lsx/pr123117.c
>
> diff --git a/gcc/testsuite/gcc.target/loongarch/vector/lsx/pr123117.c
> b/gcc/testsuite/gcc.target/loongarch/vector/lsx/pr123117.c
> new file mode 100644
> index 00000000000..e16a7204ef4
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/loongarch/vector/lsx/pr123117.c
> @@ -0,0 +1,17 @@
> +/* { dg-do run } */
> +/* { dg-options "-mlsx -DARCH_LOONGARCH64 -O1 -static" } */
> +
> +#define BS_VEC(type, num) type __attribute__((vector_size(num *
> sizeof(type))))
> +#define T BS_VEC(unsigned, 4)
> +
> +int main ()
> +{
> + BS_VEC(long int, 2) BS_VAR_0[1];
> + BS_VEC(int, 4) tt = (BS_VEC(int, 4)){0x9e47d3d2, 0, 0, 0};
> + asm("":"+f"(tt));
> + BS_VEC(unsigned int, 2) SHUF = __builtin_shufflevector((T)tt, (T)tt, 0, 1);
> + BS_VAR_0[0] = __builtin_convertvector(SHUF, BS_VEC(long int, 2));
> +
> + if (BS_VAR_0[0][0] != 0x000000009e47d3d2)
> + __builtin_abort ();
> +}
> diff --git a/gcc/tree-ssa-forwprop.cc b/gcc/tree-ssa-forwprop.cc
> index 2200fc04918..17bfa2a99dc 100644
> --- a/gcc/tree-ssa-forwprop.cc
> +++ b/gcc/tree-ssa-forwprop.cc
> @@ -3848,6 +3848,7 @@ simplify_vector_constructor (gimple_stmt_iterator *gsi)
>
> orig[0] = NULL;
> orig[1] = NULL;
> + tree orig_elem_type[2] = {};
> conv_code = ERROR_MARK;
> bool maybe_ident = true;
> bool maybe_blend[2] = { true, true };
> @@ -3902,6 +3903,11 @@ simplify_vector_constructor (gimple_stmt_iterator *gsi)
> if (j < 2)
> {
> orig[j] = ref;
> + /* Track what element type was actually extracted (which may
> + differ in signedness from the vector's element type due to
> + tree_nop_conversion_p). */
> + if (!orig_elem_type[j])
> + orig_elem_type[j] = TREE_TYPE (op1);
> if (elem != i || j != 0)
> maybe_ident = false;
> if (elem != i)
> @@ -4011,6 +4017,9 @@ simplify_vector_constructor (gimple_stmt_iterator *gsi)
> if (CONVERT_EXPR_CODE_P (conv_code)
> && (2 * TYPE_PRECISION (TREE_TYPE (TREE_TYPE (orig[0])))
> == TYPE_PRECISION (TREE_TYPE (type)))
> + && orig_elem_type[0]
> + && useless_type_conversion_p (orig_elem_type[0],
> + TREE_TYPE (type))
> && mode_for_vector (as_a <scalar_mode>
> (TYPE_MODE (TREE_TYPE (TREE_TYPE
> (orig[0])))),
> nelts * 2).exists ()
> @@ -4050,6 +4059,9 @@ simplify_vector_constructor (gimple_stmt_iterator *gsi)
> else if (CONVERT_EXPR_CODE_P (conv_code)
> && (TYPE_PRECISION (TREE_TYPE (TREE_TYPE (orig[0])))
> == 2 * TYPE_PRECISION (TREE_TYPE (type)))
> + && orig_elem_type[0]
> + && useless_type_conversion_p (orig_elem_type[0],
> + TREE_TYPE (type))
> && mode_for_vector (as_a <scalar_mode>
> (TYPE_MODE
> (TREE_TYPE (TREE_TYPE (orig[0])))),
> --
> 2.51.1
>
