[gcc r14-4588] tree-optimization/111764 - wrong reduction vectorization

[Richard Biener]

https://gcc.gnu.org/g:05f98310b54da95e468d799f4a910174320cccbb

commit r14-4588-g05f98310b54da95e468d799f4a910174320cccbb
Author: Richard Biener <rguenther@suse.de>
Date:   Thu Oct 12 09:09:46 2023 +0200

    tree-optimization/111764 - wrong reduction vectorization
    
    The following removes a misguided attempt to allow x + x in a reduction
    path, also allowing x * x which isn't valid.  x + x actually never
    arrives this way but instead is canonicalized to 2 * x.  This makes
    reduction path handling consistent with how we handle the single-stmt
    reduction case.
    
            PR tree-optimization/111764
            * tree-vect-loop.cc (check_reduction_path): Remove the attempt
            to allow x + x via special-casing of assigns.
    
            * gcc.dg/vect/pr111764.c: New testcase.

Diff:
---
 gcc/testsuite/gcc.dg/vect/pr111764.c | 16 ++++++++++++++++
 gcc/tree-vect-loop.cc                | 15 +++------------
 2 files changed, 19 insertions(+), 12 deletions(-)

diff --git a/gcc/testsuite/gcc.dg/vect/pr111764.c b/gcc/testsuite/gcc.dg/vect/pr111764.c
new file mode 100644
index 00000000000..f4e110f3bbf
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vect/pr111764.c
@@ -0,0 +1,16 @@
+#include "tree-vect.h"
+
+short b = 2;
+
+int main()
+{
+  check_vect ();
+
+  for (int a = 1; a <= 9; a++)
+    b = b * b;
+  if (b != 0)
+    __builtin_abort ();
+
+  return 0;
+}
+
diff --git a/gcc/tree-vect-loop.cc b/gcc/tree-vect-loop.cc
index 23c6e8259e7..82b793db74b 100644
--- a/gcc/tree-vect-loop.cc
+++ b/gcc/tree-vect-loop.cc
@@ -3986,24 +3986,15 @@ pop:
 	 ???  We could relax this and handle arbitrary live stmts by
 	 forcing a scalar epilogue for example.  */
       imm_use_iterator imm_iter;
+      use_operand_p use_p;
       gimple *op_use_stmt;
       unsigned cnt = 0;
       FOR_EACH_IMM_USE_STMT (op_use_stmt, imm_iter, op.ops[opi])
 	if (!is_gimple_debug (op_use_stmt)
 	    && (*code != ERROR_MARK
 		|| flow_bb_inside_loop_p (loop, gimple_bb (op_use_stmt))))
-	  {
-	    /* We want to allow x + x but not x < 1 ? x : 2.  */
-	    if (is_gimple_assign (op_use_stmt)
-		&& gimple_assign_rhs_code (op_use_stmt) == COND_EXPR)
-	      {
-		use_operand_p use_p;
-		FOR_EACH_IMM_USE_ON_STMT (use_p, imm_iter)
-		  cnt++;
-	      }
-	    else
-	      cnt++;
-	  }
+	  FOR_EACH_IMM_USE_ON_STMT (use_p, imm_iter)
+	    cnt++;
       if (cnt != 1)
 	{
 	  fail = true;