Hi,
GCC happily transforms (float)-z into -(float)z, even when z is of
unsigned type (when it's larger than float). That's wrong (the result
should always be positive, because -z is). It seems to me that this bug
exists in all reasonably recent GCC versions. The checking in
convert_to_real is wrong, it compares type precisions of different
classed types. The change with the least impact is to reject only
TYPE_UNSIGNED inner types, but perhaps it would be better to only do the
transformation if the inner type is FLOAT_TYPE_P as well.
Regstrapping on x86-64 in progress. Okay for trunk?
Ciao,
Michael.
PR middle-end/57886
* convert.c (convert_to_real): Reject unsigned inner types.
testsuite/
* c-c++-common/pr57886.c: New test.
Index: convert.c
===================================================================
--- convert.c (revision 200240)
+++ convert.c (working copy)
@@ -213,10 +213,11 @@ convert_to_real (tree type, tree expr)
switch (TREE_CODE (expr))
{
/* Convert (float)-x into -(float)x. This is safe for
- round-to-nearest rounding mode. */
+ round-to-nearest rounding mode when the inner type is signed. */
case ABS_EXPR:
case NEGATE_EXPR:
if (!flag_rounding_math
+ && !TYPE_UNSIGNED (itype)
&& TYPE_PRECISION (type) < TYPE_PRECISION (TREE_TYPE (expr)))
return build1 (TREE_CODE (expr), type,
fold (convert_to_real (type,
Index: testsuite/c-c++-common/pr57886.c
===================================================================
--- testsuite/c-c++-common/pr57886.c (revision 0)
+++ testsuite/c-c++-common/pr57886.c (working copy)
@@ -0,0 +1,12 @@
+/* { dg-do run } */
+
+float global;
+int main()
+{
+ unsigned long z = 1;
+ float x = -z;
+ global = x;
+ if (global < 0)
+ __builtin_abort ();
+ return 0;
+}
