[gcc r17-2950] vect: when REALPART/IMAGPART also check their def stmts [PR126593]

https://gcc.gnu.org/g:987e38794015c2dbb5f16d7641491d3b62680743

commit r17-2950-g987e38794015c2dbb5f16d7641491d3b62680743
Author: Tamar Christina <[email protected]>
Date:   Tue Aug 4 15:35:26 2026 +0100

    vect: when REALPART/IMAGPART also check their def stmts [PR126593]
    
    The check in compatible_complex_nodes_p is a bit too loose in that we assumed
    that when we see a REAL/IMAG pair of statement in a TWO_OPERANDS they must have
    come from the same defining statement.
    
    This is of course too loose and the operands should be checked explicitly.
    
    gcc/ChangeLog:
    
            PR tree-optimization/126593
            * tree-vect-slp-patterns.cc (compatible_complex_nodes_p): Check def
            stmts of real and imag pairs.
    
    gcc/testsuite/ChangeLog:
    
            PR tree-optimization/126593
            * gcc.target/aarch64/pr126593.c: New test.

Diff:
---
 gcc/testsuite/gcc.target/aarch64/pr126593.c | 37 +++++++++++++++++++++++++++++
 gcc/tree-vect-slp-patterns.cc               |  4 +++-
 2 files changed, 40 insertions(+), 1 deletion(-)

diff --git a/gcc/testsuite/gcc.target/aarch64/pr126593.c b/gcc/testsuite/gcc.target/aarch64/pr126593.c
new file mode 100644
index 000000000000..fce64d4d3393
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/pr126593.c
@@ -0,0 +1,37 @@
+/* { dg-do run { target arm_v8_3a_complex_neon_hw } } */
+/* { dg-require-effective-target aarch64_little_endian } */
+/* { dg-options "-O3 -march=armv8.3-a -ffast-math" } */
+
+#define N 64
+_Complex float a[N], b[N], d[N], c[N];
+
+__attribute__((noipa))
+void
+mix (int n)
+{
+  for (int i = 0; i < n; i++)
+    {
+      __real__ c[i] = __real__ a[i] * __real__ b[i] - __imag__ a[i] * __imag__ d[i];
+      __imag__ c[i] = __real__ a[i] * __imag__ b[i] + __imag__ a[i] * __real__ d[i];
+    }
+}
+
+int
+main (void)
+{
+  for (int i = 0; i < N; i++)
+    {
+      a[i] = 1.0f + 2.0fi;
+      b[i] = 3.0f + 4.0fi;
+      d[i] = 5.0f + 6.0fi;
+    }
+
+  mix (N);
+
+  /* scalar: re = 1*3 - 2*6 = -9, im = 1*4 + 2*5 = 14.
+     vectorized as a*b: re = -5, im = 10.  */
+  if (__real__ c[0] != -9.0f || __imag__ c[0] != 14.0f)
+    __builtin_abort ();
+
+  return 0;
+}
diff --git a/gcc/tree-vect-slp-patterns.cc b/gcc/tree-vect-slp-patterns.cc
index c6cf44cfd0d3..f77993100ad1 100644
--- a/gcc/tree-vect-slp-patterns.cc
+++ b/gcc/tree-vect-slp-patterns.cc
@@ -788,7 +788,9 @@ compatible_complex_nodes_p (slp_compat_nodes_map_t *compat_cache,
       tree_code acode = gimple_assign_rhs_code (a_stmt);
       tree_code bcode = gimple_assign_rhs_code (b_stmt);
       if ((acode == REALPART_EXPR || acode == IMAGPART_EXPR)
-	  && (bcode == REALPART_EXPR || bcode == IMAGPART_EXPR))
+	  && (bcode == REALPART_EXPR || bcode == IMAGPART_EXPR)
+	  && operand_equal_p (TREE_OPERAND (gimple_assign_rhs1 (a_stmt), 0),
+			      TREE_OPERAND (gimple_assign_rhs1 (b_stmt), 0)))
 	return true;
 
       if (acode != bcode)