[gcc r12-6182] tree-optimization/66502 - add testcase

[Richard Biener]

https://gcc.gnu.org/g:cd83fd98a7e769ac7ded28377984f68238812a26

commit r12-6182-gcd83fd98a7e769ac7ded28377984f68238812a26
Author: Richard Biener <rguenther@suse.de>
Date:   Mon Jan 3 10:48:57 2022 +0100

    tree-optimization/66502 - add testcase
    
    This adds the second testcase which we now also handle eliminating
    a redundant PHI node.
    
    2022-01-03  Richard Biener  <rguenther@suse.de>
    
            PR tree-optimization/66502
            * gcc.dg/tree-ssa/ssa-fre-98.c: New testcase.

Diff:
---
 gcc/testsuite/gcc.dg/tree-ssa/ssa-fre-98.c | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/gcc/testsuite/gcc.dg/tree-ssa/ssa-fre-98.c b/gcc/testsuite/gcc.dg/tree-ssa/ssa-fre-98.c
new file mode 100644
index 00000000000..3d286099b25
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/ssa-fre-98.c
@@ -0,0 +1,18 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-fre1-details" } */
+
+int foo (int a, int s, unsigned int k)
+{
+  int i = a, j = a;
+  do
+    {
+      i += s;
+      j += j;
+      j -= a;
+    }
+  while (k--);
+  return j+i;
+}
+
+/* We want the redundant PHI for j to disappear.  */
+/* { dg-final { scan-tree-dump "Replaced redundant PHI node defining j" "fre1" } } */