On 2026-07-21 20:02, Andrea Pinski wrote:
On Sun, Jul 19, 2026 at 11:32 PM Torbjörn Svensson via Sourceware
Forge <[email protected]> wrote:
From: Torbjörn SVENSSON <[email protected]>
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.
Ok.
Pushed as r17-2604-g3e2b0fcab75527.
I'll pick this commit for releases/gcc-16 and releases/gcc-15 on Friday unless
someone objects.
Kind regards,
Torbjörn
gcc/testsuite/ChangeLog:
* g++.dg/tree-ssa/pr124663.C: New test.
Signed-off-by: Torbjörn SVENSSON <[email protected]>
---
gcc/match.pd | 16 +++++++++++++++-
gcc/testsuite/g++.dg/tree-ssa/pr124663.C | 13 +++++++++++++
2 files changed, 28 insertions(+), 1 deletion(-)
create mode 100644 gcc/testsuite/g++.dg/tree-ssa/pr124663.C
diff --git a/gcc/match.pd b/gcc/match.pd
index b3738fdde1da..df9689131b65 100644
--- a/gcc/match.pd
+++ b/gcc/match.pd
@@ -7119,7 +7119,21 @@ 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" } }
--
2.54.0
