[PATCH] Fix PR51760

[Richard Guenther]

We can't directly drop to VARYING from UNDEFINED in likely_value
as an UNDEFINED value can later become CONSTANT which would make
us go up the lattice.

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

Richard.

2012-01-05  Richard Guenther  <rguenther@suse.de>

	PR tree-optimization/51760
	* tree-ssa-ccp.c (likely_value): Drop UNDEFINED to CONSTANT,
	not VARYING.
	(bit_value_unop): Handle UNDEFINED operands.
	(bit_value_binop): Likewise.

	* gcc.dg/torture/pr51760.c: New testcase.

Index: gcc/tree-ssa-ccp.c
===================================================================
--- gcc/tree-ssa-ccp.c	(revision 182901)
+++ gcc/tree-ssa-ccp.c	(working copy)
@@ -657,9 +657,10 @@ likely_value (gimple stmt)
 	}
     }
   /* If there was an UNDEFINED operand but the result may be not UNDEFINED
-     fall back to VARYING even if there were CONSTANT operands.  */
+     fall back to CONSTANT.  During iteration UNDEFINED may still drop
+     to CONSTANT.  */
   if (has_undefined_operand)
-    return VARYING;
+    return CONSTANT;
 
   /* We do not consider virtual operands here -- load from read-only
      memory may have only VARYING virtual operands, but still be
@@ -1368,6 +1369,10 @@ bit_value_unop (enum tree_code code, tre
   prop_value_t rval = get_value_for_expr (rhs, true);
   double_int value, mask;
   prop_value_t val;
+
+  if (rval.lattice_val == UNDEFINED)
+    return rval;
+
   gcc_assert ((rval.lattice_val == CONSTANT
 	       && TREE_CODE (rval.value) == INTEGER_CST)
 	      || double_int_minus_one_p (rval.mask));
@@ -1399,6 +1404,16 @@ bit_value_binop (enum tree_code code, tr
   prop_value_t r2val = get_value_for_expr (rhs2, true);
   double_int value, mask;
   prop_value_t val;
+
+  if (r1val.lattice_val == UNDEFINED
+      || r2val.lattice_val == UNDEFINED)
+    {
+      val.lattice_val = VARYING;
+      val.value = NULL_TREE;
+      val.mask = double_int_minus_one;
+      return val;
+    }
+
   gcc_assert ((r1val.lattice_val == CONSTANT
 	       && TREE_CODE (r1val.value) == INTEGER_CST)
 	      || double_int_minus_one_p (r1val.mask));
Index: gcc/testsuite/gcc.dg/torture/pr51760.c
===================================================================
--- gcc/testsuite/gcc.dg/torture/pr51760.c	(revision 0)
+++ gcc/testsuite/gcc.dg/torture/pr51760.c	(revision 0)
@@ -0,0 +1,19 @@
+/* { dg-do compile } */
+
+extern inline __attribute__ ((always_inline)) void *
+memmove (void *dest, const void *src, __SIZE_TYPE__ len)
+{
+  return __builtin___memmove_chk (dest, src, len,
+				  __builtin_object_size (dest, 0));
+}
+
+void
+foo (void)
+{
+  char a[64], *b;
+  for (;;)
+    {
+      memmove (a, b, 0);
+      b = a;
+    }
+}