[Bug c/33292] optimizer optimizes out a piece of code

["nicolas at dyalog dot com" <gcc-bugzilla at gcc dot gnu dot org>]

------- 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=14153&action=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 1.000000 seconds
Slept -1188821606.219786 seconds

Output of debug version :
Going to sleep 1.000000 seconds
Slept 1.004632 seconds


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33292