[Bug tree-optimization/56051] Wrong expression evaluation
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56051 Jakub Jelinek jakub at gcc dot gnu.org changed: What|Removed |Added Status|ASSIGNED|RESOLVED Resolution||FIXED Target Milestone|4.6.4 |4.7.3 --- Comment #11 from Jakub Jelinek jakub at gcc dot gnu.org 2013-04-12 16:29:07 UTC --- The 4.6 branch has been closed, fixed in GCC 4.7.3.
[Bug tree-optimization/56051] Wrong expression evaluation
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56051 --- Comment #9 from Jakub Jelinek jakub at gcc dot gnu.org 2013-02-01 14:11:54 UTC --- Author: jakub Date: Fri Feb 1 14:11:46 2013 New Revision: 195658 URL: http://gcc.gnu.org/viewcvs?root=gccview=revrev=195658 Log: Backported from mainline 2013-01-21 Jakub Jelinek ja...@redhat.com PR tree-optimization/56051 * fold-const.c (fold_binary_loc): Don't fold X (cast) (1 Y) into (X Y) != 0 if cast is either a narrowing conversion, or widening conversion from signed to unsigned. * gcc.c-torture/execute/pr56051.c: New test. Added: branches/gcc-4_7-branch/gcc/testsuite/gcc.c-torture/execute/pr56051.c Modified: branches/gcc-4_7-branch/gcc/ChangeLog branches/gcc-4_7-branch/gcc/fold-const.c branches/gcc-4_7-branch/gcc/testsuite/ChangeLog
[Bug tree-optimization/56051] Wrong expression evaluation
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56051 Jakub Jelinek jakub at gcc dot gnu.org changed: What|Removed |Added Known to work||4.7.3 --- Comment #10 from Jakub Jelinek jakub at gcc dot gnu.org 2013-02-01 14:33:08 UTC --- Fixed for 4.7.3+ too.
[Bug tree-optimization/56051] Wrong expression evaluation
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56051 --- Comment #7 from Jakub Jelinek jakub at gcc dot gnu.org 2013-01-21 17:55:46 UTC --- Author: jakub Date: Mon Jan 21 17:55:34 2013 New Revision: 195343 URL: http://gcc.gnu.org/viewcvs?root=gccview=revrev=195343 Log: PR tree-optimization/56051 * fold-const.c (fold_binary_loc): Don't fold X (cast) (1 Y) into (X Y) != 0 if cast is either a narrowing conversion, or widening conversion from signed to unsigned. * gcc.c-torture/execute/pr56051.c: New test. Added: trunk/gcc/testsuite/gcc.c-torture/execute/pr56051.c Modified: trunk/gcc/ChangeLog trunk/gcc/fold-const.c trunk/gcc/testsuite/ChangeLog
[Bug tree-optimization/56051] Wrong expression evaluation
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56051 --- Comment #8 from Jakub Jelinek jakub at gcc dot gnu.org 2013-01-21 18:01:59 UTC --- Fixed on the trunk so far.
[Bug tree-optimization/56051] Wrong expression evaluation
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56051 Jakub Jelinek jakub at gcc dot gnu.org changed: What|Removed |Added CC||jakub at gcc dot gnu.org Component|middle-end |tree-optimization Target Milestone|--- |4.6.4
[Bug tree-optimization/56051] Wrong expression evaluation
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56051 Jakub Jelinek jakub at gcc dot gnu.org changed: What|Removed |Added Status|NEW |ASSIGNED AssignedTo|unassigned at gcc dot |jakub at gcc dot gnu.org |gnu.org | --- Comment #3 from Jakub Jelinek jakub at gcc dot gnu.org 2013-01-20 16:46:04 UTC --- Created attachment 29227 -- http://gcc.gnu.org/bugzilla/attachment.cgi?id=29227 gcc48-pr56051.patch Untested fix. As the testcase shows, also a widening conversion can be a problem, if it extends from signed integral type to wider unsigned one, because then for Y equal to bitsize of the narrower type - 1 we get more than one bit set. On the other side, the optimization doesn't hit when X isn't an ARRAY_REF, but just an integral variable, because then arg0 and arg1 are swapped. Guess for 4.9 we should handle those cases too.
[Bug tree-optimization/56051] Wrong expression evaluation
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56051 --- Comment #4 from Marc Glisse glisse at gcc dot gnu.org 2013-01-20 18:09:40 UTC --- (In reply to comment #3) Untested fix. As the testcase shows, also a widening conversion can be a problem, if it extends from signed integral type to wider unsigned one, because then for Y equal to bitsize of the narrower type - 1 we get more than one bit set. I assume this is because of the gcc extension documented as: GCC does not use the latitude given in C99 only to treat certain aspects of signed `' as undefined, but this is subject to change. which prevents from assuming that 1n is positive. Maybe that can be changed at some point, as the documentation suggests? ;-) PS: sorry for setting it to the middle-end component, I mistakenly believed that tree-optimization was only for SSA.
[Bug tree-optimization/56051] Wrong expression evaluation
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56051 --- Comment #5 from Jakub Jelinek jakub at gcc dot gnu.org 2013-01-20 18:35:20 UTC --- Yeah, I'm afraid assuming you never do 1 31 is going to break simply way too much code in the wild.
[Bug tree-optimization/56051] Wrong expression evaluation
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56051 --- Comment #6 from Marc Glisse glisse at gcc dot gnu.org 2013-01-20 20:17:31 UTC --- (In reply to comment #5) Yeah, I'm afraid assuming you never do 1 31 is going to break simply way too much code in the wild. I noticed that clang warns for 1 31, and with -fsanitize=shift tells you if there is 1n with n==31 in C, but not in C++. And the reason seems to be that the C++ committee has, in DR1457, retroactively made it legal :-( (PR52119 also mentions this)
