https://gcc.gnu.org/g:9acbae69609a41df0f20db6222842414a85067ea
commit r17-2739-g9acbae69609a41df0f20db6222842414a85067ea Author: Kyrylo Tkachov <[email protected]> Date: Sun Jul 26 05:18:52 2026 -0700 middle-end: look through VEC_DUPLICATE_EXPR in ssa_uniform_vector_p ssa_uniform_vector_p is documented as returning the element a uniform vector is a splat from, and it handles VEC_DUPLICATE_EXPR when it is handed the bare tree. It did not handle the much more common gimple form, where the splat is the RHS of an SSA definition: VEC_DUPLICATE_EXPR is a unary operation, so gimple_assign_single_p is false for it and the SSA_NAME path fell through to NULL_TREE. Splats started reaching the helper in that form with r17-2019-g770ff476d06f ("aarch64: Port NEON vector creation intrinsics to pragma-based framework"), after which vdup_n_u8 and friends fold to uniform_vec_5 = [vec_duplicate_expr] _1; rather than to a CONSTRUCTOR, so ssa_uniform_vector_p stopped seeing through them. Callers that lose out are the lowpart-to-highpart NEON builtin fold in the aarch64 back end, vector shift and division lowering in tree-vect-generic.cc, and the CONSTRUCTOR-of-splats simplification in tree-ssa-forwprop.cc. For gcc.target/aarch64/simd/fold_to_highpart_7.c this restores ldr q0, [x1] ld1r {v31.16b}, [x0] umull2 v0.8h, v0.16b, v31.16b in place of a lowpart umull with the highpart fold missed. Bootstrapped and tested on aarch64-none-linux-gnu. gcc/ChangeLog: * tree.cc (ssa_uniform_vector_p): Look through a VEC_DUPLICATE_EXPR SSA definition. Signed-off-by: Kyrylo Tkachov <[email protected]> Diff: --- gcc/tree.cc | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/gcc/tree.cc b/gcc/tree.cc index b80068093225..c8aa42b3e10e 100644 --- a/gcc/tree.cc +++ b/gcc/tree.cc @@ -10878,6 +10878,11 @@ ssa_uniform_vector_p (tree op) gimple *def_stmt = SSA_NAME_DEF_STMT (op); if (gimple_assign_single_p (def_stmt)) return uniform_vector_p (gimple_assign_rhs1 (def_stmt)); + /* A VEC_DUPLICATE_EXPR is a unary assignment, so it is not covered + by the gimple_assign_single_p case above. */ + if (is_gimple_assign (def_stmt) + && gimple_assign_rhs_code (def_stmt) == VEC_DUPLICATE_EXPR) + return gimple_assign_rhs1 (def_stmt); } return NULL_TREE; }
