[Bug c/33292] optimizer optimizes out a piece of code
--- Comment #1 from nicolas at dyalog dot com 2007-09-03 12:26 --- Created an attachment (id=14153) -- (http://gcc.gnu.org/bugzilla/attachment.cgi?id=14153action=view) preprocessed source of a repro Sorry guys the repro is a bit complicated but i could NOT narrow it down any further. I can't understand what triggers this optimizer bug. I refer to the optimized version when compiled with : gcc delayopt.i -o delayopt -O3 -ggdb3 -Wall And to the debug version when compiled with : gcc delayopt.i -o delayopt -ggdb3 -Wall The function that the optimizer skips is TimeValToFileTime(). If you look at the optimized disassembly, you will see that asyncSleep() does the follwing routine which is the optimized call to TimeValToFileTime() : 400675: imul $0x989680,%rax,%rax 40067c: lea(%rbx,%rbx,4),%rbx 400680: lea(%rax,%rbx,2),%rbx whereas nt_async_delay() doesn't and therefore uses a bad value for the variable curr. Output of optimized version : Going to sleep 1.00 seconds Slept -1188821606.219786 seconds Output of debug version : Going to sleep 1.00 seconds Slept 1.004632 seconds -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33292
[Bug c/33292] optimizer optimizes out a piece of code
--- Comment #2 from nicolas at dyalog dot com 2007-09-03 14:07 --- after a bit more work it seems optimized out because diff64() doesn't observe strict aliasing... that was tricky because it was not the diff64() code that was snipped out but TimeValToFileTime()... I think the compiler should either warn (strict aliasing) in diff64, or not remove TimeValToFileTime()... Or did I miss something ? -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33292
[Bug c/33292] optimizer optimizes out a piece of code
--- Comment #3 from rguenth at gcc dot gnu dot org 2007-09-03 15:20 --- The cast to (void *) disables the alias warning. This was done on purpose, so it's unfortunate that this in some cases makes debugging harder. *** This bug has been marked as a duplicate of 21920 *** -- rguenth at gcc dot gnu dot org changed: What|Removed |Added Status|UNCONFIRMED |RESOLVED Resolution||DUPLICATE http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33292
[Bug c/33292] optimizer optimizes out a piece of code
--- Comment #4 from nicolas at dyalog dot com 2007-09-03 16:08 --- That's what I feared I have lots of those in my code... Thanks for the quick reply anyway =) -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33292
