* Fix PR57886, invalid folding of conversion
@ 2013-07-12 13:37 Michael Matz
2013-07-12 14:03 ` Michael Matz
2013-07-12 14:54 ` Marc Glisse
0 siblings, 2 replies; 5+ messages in thread
From: Michael Matz @ 2013-07-12 13:37 UTC (permalink / raw)
To: gcc-patches
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;
+}
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: Fix PR57886, invalid folding of conversion
2013-07-12 13:37 Fix PR57886, invalid folding of conversion Michael Matz
@ 2013-07-12 14:03 ` Michael Matz
2013-07-12 14:09 ` Jakub Jelinek
2013-07-12 14:54 ` Marc Glisse
1 sibling, 1 reply; 5+ messages in thread
From: Michael Matz @ 2013-07-12 14:03 UTC (permalink / raw)
To: gcc-patches
Hi,
On Fri, 12 Jul 2013, Michael Matz wrote:
> 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.
So, this is a dup of PR55771, I'm now proposing to add a test for
FLOAT_TYPE_P, not TYPE_UNSIGNED. Restarted the regstrap.
Ciao,
Michael.
--
PR middle-end/55771
* convert.c (convert_to_real): Reject non-float inner types.
testsuite/
* c-c++-common/pr55771.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 float. */
case ABS_EXPR:
case NEGATE_EXPR:
if (!flag_rounding_math
+ && FLOAT_TYPE_P (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/pr55771.c
===================================================================
--- testsuite/c-c++-common/pr55771.c (revision 0)
+++ testsuite/c-c++-common/pr55771.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;
+}
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: Fix PR57886, invalid folding of conversion
2013-07-12 14:03 ` Michael Matz
@ 2013-07-12 14:09 ` Jakub Jelinek
0 siblings, 0 replies; 5+ messages in thread
From: Jakub Jelinek @ 2013-07-12 14:09 UTC (permalink / raw)
To: Michael Matz; +Cc: gcc-patches
On Fri, Jul 12, 2013 at 03:37:44PM +0200, Michael Matz wrote:
> So, this is a dup of PR55771, I'm now proposing to add a test for
> FLOAT_TYPE_P, not TYPE_UNSIGNED. Restarted the regstrap.
Ok if it passes bootstrap/regtest. I'd say we should apply it to
4.8 too, while it might not be a regression (or at least not a recent one),
it is a silent wrong-code issue. Sorry for forgetting about this PR.
> PR middle-end/55771
> * convert.c (convert_to_real): Reject non-float inner types.
>
> testsuite/
> * c-c++-common/pr55771.c: New test.
Jakub
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: Fix PR57886, invalid folding of conversion
2013-07-12 13:37 Fix PR57886, invalid folding of conversion Michael Matz
2013-07-12 14:03 ` Michael Matz
@ 2013-07-12 14:54 ` Marc Glisse
2013-07-12 16:12 ` Michael Matz
1 sibling, 1 reply; 5+ messages in thread
From: Marc Glisse @ 2013-07-12 14:54 UTC (permalink / raw)
To: Michael Matz; +Cc: gcc-patches
On Fri, 12 Jul 2013, Michael Matz wrote:
> 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.
If you want to handle integers, shouldn't you test TYPE_OVERFLOW_UNDEFINED
(for LONG_MIN)? FLOAT_TYPE_P does seem safer indeed.
I'd replace TREE_TYPE (expr) with itype on the next line, it is confusing
to refer to it under 2 different names on 2 consecutive lines.
--
Marc Glisse
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: Fix PR57886, invalid folding of conversion
2013-07-12 14:54 ` Marc Glisse
@ 2013-07-12 16:12 ` Michael Matz
0 siblings, 0 replies; 5+ messages in thread
From: Michael Matz @ 2013-07-12 16:12 UTC (permalink / raw)
To: gcc-patches
Hi,
On Fri, 12 Jul 2013, Marc Glisse wrote:
> If you want to handle integers, shouldn't you test TYPE_OVERFLOW_UNDEFINED
> (for LONG_MIN)?
Right, ...
> FLOAT_TYPE_P does seem safer indeed.
... hence this is it now.
>
> I'd replace TREE_TYPE (expr) with itype on the next line, it is confusing to
> refer to it under 2 different names on 2 consecutive lines.
True, I made that change. r200926.
Ciao,
Michael.
^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2013-07-12 15:42 UTC | newest]
Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2013-07-12 13:37 Fix PR57886, invalid folding of conversion Michael Matz
2013-07-12 14:03 ` Michael Matz
2013-07-12 14:09 ` Jakub Jelinek
2013-07-12 14:54 ` Marc Glisse
2013-07-12 16:12 ` Michael Matz
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).