[PATCH] Fix PR63962

[PATCH] Fix PR63962

[Richard Biener]

When moving tree-ssa-forwprop.c:associate_plusminus to match.pd patterns
a single-use restriction escaped my eye.  It is indeed important
for non-simplifications like
  (ptr p+ off1) p+ off2 -> ptr p+ (off1 + off2)
to not un-CSE.  The association is most useful to enable later
re-association as reassoc isn't able to associate pointer-plus
chains but only unsigned integer arithmetic.

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

Richard.

2014-11-20  Richard Biener  <rguenther@suse.de>

	PR middle-end/63962
	* match.pd ((p +p off1) +p off2 -> (p +p (off1 + off2))):
	Guard with single-use operand 0.

	* gcc.dg/tree-ssa/forwprop-30.c: New testcase.

Index: gcc/match.pd
===================================================================
--- gcc/match.pd	(revision 217767)
+++ gcc/match.pd	(working copy)
@@ -370,8 +370,9 @@ (define_operator_list inverted_tcc_compa
 
 /* Associate (p +p off1) +p off2 as (p +p (off1 + off2)).  */
 (simplify
-  (pointer_plus (pointer_plus @0 @1) @3)
-  (pointer_plus @0 (plus @1 @3)))
+  (pointer_plus (pointer_plus@2 @0 @1) @3)
+  (if (TREE_CODE (@2) != SSA_NAME || has_single_use (@2))
+   (pointer_plus @0 (plus @1 @3))))
 
 /* Pattern match
      tem1 = (long) ptr1;
Index: gcc/testsuite/gcc.dg/tree-ssa/forwprop-30.c
===================================================================
--- gcc/testsuite/gcc.dg/tree-ssa/forwprop-30.c	(revision 0)
+++ gcc/testsuite/gcc.dg/tree-ssa/forwprop-30.c	(working copy)
@@ -0,0 +1,15 @@
+/* { dg-do compile } */
+/* { dg-options "-O -fdump-tree-optimized" } */
+
+int *p;
+int *foo (int *q, int i, int j)
+{
+  p = q + i;
+  return p + j;
+}
+
+/* We shouldn't associate (q + i) + j to q + (i + j) here as we
+   need q + i as well.  */
+
+/* { dg-final { scan-tree-dump-times "\\+" 2 "optimized" } } */
+/* { dg-final { cleanup-tree-dump "optimized" } } */