diff mbox

[committed] Fix PR60733

Message ID 1396477097.16711.8.camel@gnopaine
State New
Headers show

Commit Message

Bill Schmidt April 2, 2014, 10:18 p.m. UTC 
PR60733 identifies a case where straight-line strength reduction
produces code that doesn't satisfy SSA verification.  For a PHI
candidate, the insertion of an initializer for a stride calculation
along an incoming arc was specified to be at the point of the feeding
definition of the PHI along that arc.  This is wrong and can place the
initializer far earlier than its operands are guaranteed to be
available.  In this case, the initializer was placed earlier in the
block than the definition of one of its operands.

In fact, the initializer is only needed at the end of the feeding block
for the PHI argument, and its operands are guaranteed to be available at
that point.  This patch changes the placement of the initializer to this
location for PHI candidates.  The nearest common dominator algorithm may
still place the initializer at an earlier point, but only if it is safe
to do so.

Bootstrapped and tested on powerpc64-unknown-linux-gnu with no new
regressions; committed.

Thanks,
Bill


[gcc]

2014-04-02  Bill Schmidt  <wschmidt@linux.vnet.ibm.com>

	PR tree-optimization/60733
	* gimple-ssa-strength-reduction.c (ncd_with_phi): Change required
	insertion point for PHI candidates to be the end of the feeding
	block for the PHI argument.

[gcc/testsuite]

2014-04-02  Bill Schmidt  <wschmidt@linux.vnet.ibm.com>

	PR tree-optimization/60733
	* gcc.dg/torture/pr60733.c:  New test.
diff mbox

Patch

Index: gcc/testsuite/gcc.dg/torture/pr60733.c
===================================================================
--- gcc/testsuite/gcc.dg/torture/pr60733.c	(revision 0)
+++ gcc/testsuite/gcc.dg/torture/pr60733.c	(revision 0)
@@ -0,0 +1,36 @@ 
+/* { dg-do run } */
+
+int a, d, e, f, g, h, i, j, k;
+unsigned short b;
+
+short
+fn1 (int p1, int p2)
+{
+  return p1 * p2;
+}
+
+int
+main ()
+{
+  for (; a; a--)
+    {
+      int l = 0;
+      if (f >= 0)
+	{
+	  for (; h;)
+	    e = 0;
+	  for (; l != -6; l--)
+	    {
+	      j = fn1 (b--, d);
+	      for (g = 0; g; g = 1)
+		;
+	      k = e ? 2 : 0;
+	    }
+	  i = 0;
+	  for (;;)
+	    ;
+	}
+    }
+  d = 0;
+  return 0;
+}
Index: gcc/gimple-ssa-strength-reduction.c
===================================================================
--- gcc/gimple-ssa-strength-reduction.c	(revision 209023)
+++ gcc/gimple-ssa-strength-reduction.c	(working copy)
@@ -3001,10 +3001,10 @@  ncd_with_phi (slsr_cand_t c, double_int incr, gimp
 	    {
 	      slsr_cand_t arg_cand = base_cand_from_table (arg);
 	      double_int diff = arg_cand->index - basis->index;
+	      basic_block pred = gimple_phi_arg_edge (phi, i)->src;
 
 	      if ((incr == diff) || (!address_arithmetic_p && incr == -diff))
-		ncd = ncd_for_two_cands (ncd, gimple_bb (arg_cand->cand_stmt),
-					 *where, arg_cand, where);
+		ncd = ncd_for_two_cands (ncd, pred, *where, NULL, where);
 	    }
 	}
     }