While match.pd has been changed to not transform -(-A) to A
when the overflow does not wrap or the signed integer ovreflow
checking is enabled, fold_negate_expr still happily does such
a transformation. That's bad because then we can't detect
an overflow, as on the following testcase. But I allowed this
transformation for constants, because VRP seems to rely on that
(abs_extent_range calls fold_unary).
Bootstrapped/regtested on x86_64-linux, ok for trunk?
2014-11-11 Marek Polacek <pola...@redhat.com>
* fold-const.c (fold_unary_loc): Don't call fold_negate_expr
when doing signed integer sanitization or when the type overflow
wraps.
* c-c++-common/ubsan/overflow-negate-3.c: New test.
diff --git gcc/fold-const.c gcc/fold-const.c
index f3562ff..33311fb 100644
--- gcc/fold-const.c
+++ gcc/fold-const.c
@@ -7862,9 +7862,15 @@ fold_unary_loc (location_t loc, enum tree_code code,
tree type, tree op0)
return fold_view_convert_expr (type, op0);
case NEGATE_EXPR:
- tem = fold_negate_expr (loc, arg0);
- if (tem)
- return fold_convert_loc (loc, type, tem);
+ if (TREE_CODE (arg0) == INTEGER_CST
+ || TREE_CODE (arg0) == REAL_CST
+ || TYPE_OVERFLOW_WRAPS (type)
+ || (flag_sanitize & SANITIZE_SI_OVERFLOW) == 0)
+ {
+ tem = fold_negate_expr (loc, arg0);
+ if (tem)
+ return fold_convert_loc (loc, type, tem);
+ }
return NULL_TREE;
case ABS_EXPR:
diff --git gcc/testsuite/c-c++-common/ubsan/overflow-negate-3.c
gcc/testsuite/c-c++-common/ubsan/overflow-negate-3.c
index e69de29..cf4f9bc 100644
--- gcc/testsuite/c-c++-common/ubsan/overflow-negate-3.c
+++ gcc/testsuite/c-c++-common/ubsan/overflow-negate-3.c
@@ -0,0 +1,17 @@
+/* { dg-do run } */
+/* { dg-options "-fsanitize=signed-integer-overflow" } */
+
+#define INT_MIN (-__INT_MAX__ - 1)
+
+int
+main ()
+{
+ volatile int x = INT_MIN;
+ int y = x;
+ y = -(-y);
+ x = y;
+ return 0;
+}
+
+/* { dg-output "negation of -2147483648 cannot be represented in type
'int'\[^\n\r]*; cast to an unsigned type to negate this value to
itself\[^\n\r]*(\n|\r\n|\r)" } */
+/* { dg-output "\[^\n\r]*negation of -2147483648 cannot be represented in type
'int'\[^\n\r]*; cast to an unsigned type to negate this value to
itself\[^\n\r]*(\n|\r\n|\r)" } */
Marek
