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 <rguent...@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;
+ }
+}
