https://gcc.gnu.org/g:10f6e51b8250ce4f553c055ad737607332311a5d
commit r17-2589-g10f6e51b8250ce4f553c055ad737607332311a5d Author: Richard Biener <[email protected]> Date: Mon Jul 20 13:57:36 2026 +0200 Simplify (vec_select:<scalar> (vec_concat ..)) The following adds simplification of a scalar mode vec_select wrapping a vec_concat. combine sees (insn 7 4 8 2 (set (reg:V2DF 106) (vec_concat:V2DF (plus:DF (vec_select:DF (reg/v:V2DF 101 [ p ]) (parallel [ (const_int 0 [0]) ])) (vec_select:DF (reg/v:V2DF 101 [ p ]) (parallel [ (const_int 1 [0x1]) ]))) (plus:DF (vec_select:DF (reg/v:V2DF 101 [ p ]) (parallel [ (const_int 0 [0]) ])) (vec_select:DF (reg/v:V2DF 101 [ p ]) (parallel [ (const_int 1 [0x1]) ]))))) "t.c":5:11 3234 {*sse3_haddv2df3} (expr_list:REG_DEAD (reg/v:V2DF 101 [ p ]) (nil))) (insn 8 7 9 2 (set (reg:DF 105) (vec_select:DF (reg:V2DF 106) (parallel [ (const_int 0 [0]) ]))) "t.c":5:11 7297 {sse2_storelpd} (expr_list:REG_DEAD (reg:V2DF 106) (nil))) and this should simplify and combine to (set (reg:DF 105) (plus:DF (vec_select:DF (reg:V2DF 109 [ p ]) (parallel [ (const_int 0 [0]) ])) (vec_select:DF (reg:V2DF 109 [ p ]) (parallel [ (const_int 1 [0x1]) ])))) which x86 can recognize (but rejects due to consting, see PR126328). There'll be test coverage in gcc.target/i386/pr54400.c * simplify-rtx.cc (simplify_context::simplify_binary_operation_1): Simplify scalar vec_select of vec_concat. Diff: --- gcc/simplify-rtx.cc | 14 ++++++++++++++ 1 file changed, 14 insertions(+) diff --git a/gcc/simplify-rtx.cc b/gcc/simplify-rtx.cc index 882a11c5760d..6f8ee53f209f 100644 --- a/gcc/simplify-rtx.cc +++ b/gcc/simplify-rtx.cc @@ -5210,6 +5210,20 @@ simplify_ashift: tmp_op, gen_rtx_PARALLEL (VOIDmode, vec)); return tmp; } + /* If we select one half of a vec_concat, return that. */ + else if (GET_CODE (trueop0) == VEC_CONCAT) + { + rtx subop0 = XEXP (trueop0, 0); + rtx subop1 = XEXP (trueop0, 1); + machine_mode mode0 = GET_MODE (subop0); + machine_mode mode1 = GET_MODE (subop1); + int i0 = INTVAL (XVECEXP (trueop1, 0, 0)); + if (i0 == 0 && mode == mode0 && !side_effects_p (subop1)) + return subop0; + if (known_eq (i0, GET_MODE_NUNITS (mode0)) + && mode == mode1 && !side_effects_p (subop0)) + return subop1; + } } else {
