https://gcc.gnu.org/g:3e2b0fcab75527bae01a0e22fe993addcf8475d9
commit r17-2604-g3e2b0fcab75527bae01a0e22fe993addcf8475d9 Author: Torbjörn SVENSSON <[email protected]> Date: Sat Jul 18 11:00:32 2026 +0200 tree-optimization: Fold constant conditional selects [PR124663] Fold `(x == CST) ? x : CST` and `(x != CST) ? CST : x` to `CST` for integral scalar and vector types. This catches cases where earlier folding has converted bitwise mask expressions into conditional selects, including ARM MVE predicate-to-vector mask forms. PR tree-optimization/124663 gcc/ChangeLog: * match.pd: Fold constant conditional selects. gcc/testsuite/ChangeLog: * g++.dg/tree-ssa/pr124663.C: New test. Signed-off-by: Torbjörn SVENSSON <[email protected]> Diff: --- gcc/match.pd | 16 +++++++++++++++- gcc/testsuite/g++.dg/tree-ssa/pr124663.C | 13 +++++++++++++ 2 files changed, 28 insertions(+), 1 deletion(-) diff --git a/gcc/match.pd b/gcc/match.pd index 017b1362b7e4..723780b8c381 100644 --- a/gcc/match.pd +++ b/gcc/match.pd @@ -7112,7 +7112,21 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT) /* For CONDs, don't handle signed values here. */ (if (cnd == VEC_COND_EXPR || TYPE_UNSIGNED (TREE_TYPE (@0))) - (cnd @0 @2 @1)))) + (cnd @0 @2 @1))) + + /* A == CST ? A : CST -> CST. */ + (simplify + (cnd (eq @0 CONSTANT_CLASS_P@1) (nop_convert? @0) CONSTANT_CLASS_P@2) + (if (ANY_INTEGRAL_TYPE_P (type) + && operand_equal_p (@1, @2)) + (convert @1))) + + /* A != CST ? CST : A -> CST. */ + (simplify + (cnd (ne @0 CONSTANT_CLASS_P@1) CONSTANT_CLASS_P@2 (nop_convert? @0)) + (if (ANY_INTEGRAL_TYPE_P (type) + && operand_equal_p (@1, @2)) + (convert @1)))) /* abs/negative simplifications moved from fold_cond_expr_with_comparison. diff --git a/gcc/testsuite/g++.dg/tree-ssa/pr124663.C b/gcc/testsuite/g++.dg/tree-ssa/pr124663.C new file mode 100644 index 000000000000..dfd12debff95 --- /dev/null +++ b/gcc/testsuite/g++.dg/tree-ssa/pr124663.C @@ -0,0 +1,13 @@ +// PR c++/124663 +// { dg-do compile } +// { dg-options "-O2 -fdump-tree-forwprop3-raw" } + +#define vector __attribute__((vector_size(4*sizeof(int)))) +void f(vector int *a) +{ + vector int cst = {1,2,3,4}; + vector int t = (*a == cst); + *a = (t ? *a : cst); +} + +// { dg-final { scan-tree-dump-not "_expr" "forwprop3" } }
