[PATCH PR70715]Expand simple operations in IV.base and check if it's the control_IV

[Bin Cheng]

Hi,
As reported in PR70715, GCC failed to prove no-overflows of IV(&p[n]) for 
simple example like:
int
foo (char *p, unsigned n)
{
  while(n--)
    {
      p[n]='A';
    }
  return 0;
}
Actually, code has already been added to handle this form loops when fixing 
PR68529.  Problem with this case is loop niter analyzer records control_IV with 
its base expanded by calling expand_simple_operations.  This patch simply adds 
code expanding BASE before we check its equality against control_IV.base.  In 
the long run, we might want to remove the use of expand_simple_operations.

Bootstrap and test on x86_64.  Is it OK?

Thanks,
bin


2016-04-20  Bin Cheng  <bin.ch...@arm.com>

        PR tree-optimization/70715
        * tree-ssa-loop-niter.c (loop_exits_before_overflow): Check equality
        after expanding BASE using expand_simple_operations.

diff --git a/gcc/tree-ssa-loop-niter.c b/gcc/tree-ssa-loop-niter.c
index 81689fc..c61083e 100644
--- a/gcc/tree-ssa-loop-niter.c
+++ b/gcc/tree-ssa-loop-niter.c
@@ -4141,7 +4141,11 @@ loop_exits_before_overflow (tree base, tree step,
            continue;
 
          /* Done proving if this is a no-overflow control IV.  */
-         if (operand_equal_p (base, civ->base, 0))
+         if (operand_equal_p (base, civ->base, 0)
+             /* Control IV is recorded after expanding simple operations,
+                Here we compare it against expanded base too.  */
+             || operand_equal_p (expand_simple_operations (base),
+                                 civ->base, 0))
            return true;
 
          /* If this is a before stepping control IV, in other words, we have
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/scev-11.c 
b/gcc/testsuite/gcc.dg/tree-ssa/scev-11.c
new file mode 100644
index 0000000..b9223c8
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/scev-11.c
@@ -0,0 +1,15 @@
+/* { dg-do compile } */
+/* { dg-options "-O3 -fdump-tree-ldist" } */
+
+int
+foo (char *p, unsigned n)
+{
+  while(n--)
+    {
+      p[n]='A';
+    }
+  return 0;
+}
+
+/* Loop can be transformed into builtin memset since &p[n] is SCEV.  */
+/* { dg-final { scan-tree-dump "builtin_memset" "ldist" } } */