[PATCH PR72772]Also check equality for expanded iv base.

[Bin Cheng]

Hi,
Following previous patch, this one fixes PR72772 by checking equality for 
expanded iv base.  Richard is fixing the PR by removing degenerate PHI at the 
first place, but I think this one also catches more cases.
Bootstrap and test on x86_64 and AArch64.  Is it OK?

Thanks,
bin

2016-08-02  Bin Cheng  <bin.ch...@arm.com>

        PR tree-optimization/72772
        * tree-ssa-loop-niter.c (loop_exits_before_overflow): Check equality
        for expanded base.

gcc/testsuite/ChangeLog
2016-08-02  Bin Cheng  <bin.ch...@arm.com>

        PR tree-optimization/pr72772
        * gcc.dg/tree-ssa/pr72772.c: New test.
diff --git a/gcc/tree-ssa-loop-niter.c b/gcc/tree-ssa-loop-niter.c
index 2fa51ea..39183c6 100644
--- a/gcc/tree-ssa-loop-niter.c
+++ b/gcc/tree-ssa-loop-niter.c
@@ -4141,7 +4141,7 @@ loop_exits_before_overflow (tree base, tree step,
       for (civ = loop->control_ivs; civ; civ = civ->next)
        {
          enum tree_code code;
-         tree stepped, extreme, civ_type = TREE_TYPE (civ->step);
+         tree civ_type = TREE_TYPE (civ->step);
 
          /* Have to consider type difference because operand_equal_p ignores
             that for constants.  */
@@ -4154,11 +4154,13 @@ 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)
-             /* 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))
+         if (operand_equal_p (base, civ->base, 0))
+           return true;
+
+         /* Control IV is recorded after expanding simple operations,
+            Here we expand base and compare it too.  */
+         tree expanded_base = expand_simple_operations (base);
+         if (operand_equal_p (expanded_base, civ->base, 0))
            return true;
 
          /* If this is a before stepping control IV, in other words, we have
@@ -4180,9 +4182,14 @@ loop_exits_before_overflow (tree base, tree step,
          else
            code = PLUS_EXPR;
 
-         stepped = fold_build2 (code, TREE_TYPE (base), base, step);
-         if (operand_equal_p (stepped, civ->base, 0))
+         tree stepped = fold_build2 (code, TREE_TYPE (base), base, step);
+         tree expanded_stepped = fold_build2 (code, TREE_TYPE (base),
+                                              expanded_base, step);
+         if (operand_equal_p (stepped, civ->base, 0)
+             || operand_equal_p (expanded_stepped, civ->base, 0))
            {
+             tree extreme;
+
              if (tree_int_cst_sign_bit (step))
                {
                  code = LT_EXPR;
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr72772.c 
b/gcc/testsuite/gcc.dg/tree-ssa/pr72772.c
new file mode 100644
index 0000000..7aa2b59
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/pr72772.c
@@ -0,0 +1,21 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -ftree-loop-distribution -fdump-tree-ldist-details" } */
+
+int foo (int flag, char *a)
+{
+  short i, j;
+  short l = 0;
+  if (flag == 1)
+    l = 3;
+
+  for (i = 0; i < 4; i++)
+    {
+      for (j = l - 1; j > 0; j--)
+        a[j] = a[j - 1];
+      a[0] = i;
+    }
+}
+
+/* Addresses of array reference a[j] and a[j - 1] are SCEVs.  */
+/* { dg-final { scan-tree-dump-not "failed: evolution of base is not affine." 
"ldist" } } */
+