[gcc r14-9134] tree-optimization/114027 - conditional reduction chain

[Richard Biener <rguenth@gcc.gnu.org>]

https://gcc.gnu.org/g:549f251f055e3a0b0084189a3012c4f15d635e75

commit r14-9134-g549f251f055e3a0b0084189a3012c4f15d635e75
Author: Richard Biener <rguenther@suse.de>
Date:   Thu Feb 22 10:50:12 2024 +0100

    tree-optimization/114027 - conditional reduction chain
    
    When we classify a conditional reduction chain as CONST_COND_REDUCTION
    we fail to verify all involved conditionals have the same constant.
    That's a quite unlikely situation so the following simply disables
    such classification when there's more than one reduction statement.
    
            PR tree-optimization/114027
            * tree-vect-loop.cc (vecctorizable_reduction): Use optimized
            condition reduction classification only for single-element
            chains.
    
            * gcc.dg/vect/pr114027.c: New testcase.

Diff:
---
 gcc/testsuite/gcc.dg/vect/pr114027.c | 26 ++++++++++++++++++++++++++
 gcc/tree-vect-loop.cc                | 11 ++++++-----
 2 files changed, 32 insertions(+), 5 deletions(-)

diff --git a/gcc/testsuite/gcc.dg/vect/pr114027.c b/gcc/testsuite/gcc.dg/vect/pr114027.c
new file mode 100644
index 000000000000..ead9cdd982d7
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vect/pr114027.c
@@ -0,0 +1,26 @@
+#include "tree-vect.h"
+
+int __attribute__((noipa))
+foo (int *f, int n)
+{
+  int res = 0;
+  for (int i = 0; i < n; ++i)
+    {
+      if (f[2*i])
+        res = 2;
+      if (f[2*i+1])
+        res = -2;
+    }
+  return res;
+}
+
+int f[] = { 1, 1, 1, 1, 1, 1, 1, 1,
+            1, 1, 1, 1, 1, 1, 1, 0 };
+
+int
+main ()
+{
+  if (foo (f, 16) != 2)
+    __builtin_abort ();
+  return 0;
+}
diff --git a/gcc/tree-vect-loop.cc b/gcc/tree-vect-loop.cc
index 5a5865c42fc6..35f1f8c7d424 100644
--- a/gcc/tree-vect-loop.cc
+++ b/gcc/tree-vect-loop.cc
@@ -7759,17 +7759,18 @@ vectorizable_reduction (loop_vec_info loop_vinfo,
 		  < GET_MODE_SIZE (SCALAR_TYPE_MODE (TREE_TYPE (vectype_op[i]))))))
 	vectype_in = vectype_op[i];
 
-      if (op.code == COND_EXPR)
+      /* Record how the non-reduction-def value of COND_EXPR is defined.
+	 ???  For a chain of multiple CONDs we'd have to match them up all.  */
+      if (op.code == COND_EXPR && reduc_chain_length == 1)
 	{
-	  /* Record how the non-reduction-def value of COND_EXPR is defined.  */
 	  if (dt == vect_constant_def)
 	    {
 	      cond_reduc_dt = dt;
 	      cond_reduc_val = op.ops[i];
 	    }
-	  if (dt == vect_induction_def
-	      && def_stmt_info
-	      && is_nonwrapping_integer_induction (def_stmt_info, loop))
+	  else if (dt == vect_induction_def
+		   && def_stmt_info
+		   && is_nonwrapping_integer_induction (def_stmt_info, loop))
 	    {
 	      cond_reduc_dt = dt;
 	      cond_stmt_vinfo = def_stmt_info;