[gcc r16-3859] match.pd: Add missing type check to reduc(ctor) pattern [PR121772]

[Alex Coplan]

https://gcc.gnu.org/g:a7a9b7badc0ba95b510c7e61da6439fca78e31d3

commit r16-3859-ga7a9b7badc0ba95b510c7e61da6439fca78e31d3
Author: Alex Coplan <alex.coplan@arm.com>
Date:   Tue Sep 9 12:57:14 2025 +0100

    match.pd: Add missing type check to reduc(ctor) pattern [PR121772]
    
    In this PR we have a reduction of a vector constructor, where the
    type of the constructor is int16x8_t and the elements are int16x4_t;
    i.e. it is representing a concatenation of two vectors.
    
    This triggers a match.pd pattern which looks like it was written to
    handle reductions of vector constructors where the elements of the ctor
    are scalars, not vectors.  There is no type check to enforce this
    property, which leads to the pattern replacing a reduction to scalar
    with an int16x4_t vector in this case, which of course is a type error,
    leading to an invalid GIMPLE ICE.
    
    This patch adds a type check to the pattern, only going ahead with the
    transformation if the element type of the ctor matches that of the
    reduction.
    
    gcc/ChangeLog:
    
            PR tree-optimization/121772
            * match.pd: Add type check to reduc(ctor) pattern.
    
    gcc/testsuite/ChangeLog:
    
            PR tree-optimization/121772
            * gcc.target/aarch64/torture/pr121772.c: New test.

Diff:
---
 gcc/match.pd                                        | 1 +
 gcc/testsuite/gcc.target/aarch64/torture/pr121772.c | 5 +++++
 2 files changed, 6 insertions(+)

diff --git a/gcc/match.pd b/gcc/match.pd
index dbbb7b512754..8107ee6ec83c 100644
--- a/gcc/match.pd
+++ b/gcc/match.pd
@@ -11085,6 +11085,7 @@ and,
 			 ? gimple_assign_rhs1 (SSA_NAME_DEF_STMT (@0)) : @0);
 	    tree elt = ctor_single_nonzero_element (ctor); }
       (if (elt
+	   && types_match (type, TREE_TYPE (elt))
 	   && !HONOR_SNANS (type)
 	   && !HONOR_SIGNED_ZEROS (type))
 	{ elt; }))))
diff --git a/gcc/testsuite/gcc.target/aarch64/torture/pr121772.c b/gcc/testsuite/gcc.target/aarch64/torture/pr121772.c
new file mode 100644
index 000000000000..3b4cf4d7d189
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/torture/pr121772.c
@@ -0,0 +1,5 @@
+/* { dg-do compile } */
+#include <arm_neon.h>
+int16_t f(int16x4_t b) {
+  return vaddvq_s16(vcombine_s16(b, vdup_n_s16 (0)));
+}