[PATCH] Fix PR83580

[Richard Biener]

The following fixes PR83580, split_constant_offset is a somewhat odd
beast, replicating SCEV code and tree-affine a bit.  It also got
similar tricks as those with regarding to looking through conversions
but while being pedantic about overflow it simply strips sign-conversions.
That's of course wrong, thus the following patch removes that.

I do expect eventual fallout (in missed optimizations), so it needs
some baking on trunk before backporting.

Bootstrapped and tested on x86_64-unknown-linux-gnu, applied.

Richard.

2018-01-08  Richard Biener  <rguenther@suse.de>

	PR middle-end/83580
	* tree-data-ref.c (split_constant_offset): Remove STRIP_NOPS.

	* gcc.dg/torture/pr83580.c: New testcase.

Index: gcc/tree-data-ref.c
===================================================================
--- gcc/tree-data-ref.c	(revision 256275)
+++ gcc/tree-data-ref.c	(working copy)
@@ -723,23 +723,21 @@ split_constant_offset_1 (tree type, tree
 void
 split_constant_offset (tree exp, tree *var, tree *off)
 {
-  tree type = TREE_TYPE (exp), otype, op0, op1, e, o;
+  tree type = TREE_TYPE (exp), op0, op1, e, o;
   enum tree_code code;
 
   *var = exp;
   *off = ssize_int (0);
-  STRIP_NOPS (exp);
 
   if (tree_is_chrec (exp)
       || get_gimple_rhs_class (TREE_CODE (exp)) == GIMPLE_TERNARY_RHS)
     return;
 
-  otype = TREE_TYPE (exp);
   code = TREE_CODE (exp);
   extract_ops_from_tree (exp, &code, &op0, &op1);
-  if (split_constant_offset_1 (otype, op0, code, op1, &e, &o))
+  if (split_constant_offset_1 (type, op0, code, op1, &e, &o))
     {
-      *var = fold_convert (type, e);
+      *var = e;
       *off = o;
     }
 }
Index: gcc/testsuite/gcc.dg/torture/pr83580.c
===================================================================
--- gcc/testsuite/gcc.dg/torture/pr83580.c	(nonexistent)
+++ gcc/testsuite/gcc.dg/torture/pr83580.c	(working copy)
@@ -0,0 +1,16 @@
+/* { dg-do run } */
+
+int a[2] = { 0, 1 };
+int x = 129;
+
+int
+main ()
+{
+  volatile int v = 0;
+  int t = x, i;
+  for (i = 0; i < 1 + v + v + v + v + v + v + v + v + a[a[0]]; i++)
+    t = a[(signed char) (130 - x)];
+  if (t != 1)
+    __builtin_abort ();
+  return 0;
+}