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...g it :-) I can get back to it if there's interest! On Wed, Jul 29, 2015 at 4:12 PM, Reid Kleckner <rnk at google.com> wrote: > I remember this bug. :) IMO, LLVM should never emit pushf / popf. I'm not > sure this patch to fix it ever got committed: > http://reviews.llvm.org/D6629 > > > On Wed, Jul 29, 2015 at 3:11 PM, Michael Hordijk <hoffbrinkle at hotmail.com> > wrote: > >> >> Using Clang/LLVM 3.6.0 we are observing a case where the optimizations >> are clobbering EFLAGS on x86_64. This is inconvenient when the status of >> bi...

...> Agreed, never emit pushf/popf. Sorry I never committed the patch, the > cmov issue got hairy and I never got to debugging it :-) > I can get back to it if there's interest! You've definitely got some interest here. I've been looking at your patch on http://reviews.llvm.org/D6629 and I think I'm up to speed on where it's stuck. I'll shoot you an email directly unless you want to keep the effort here on the list. - michael

I remember this bug. :) IMO, LLVM should never emit pushf / popf. I'm not sure this patch to fix it ever got committed: http://reviews.llvm.org/D6629 On Wed, Jul 29, 2015 at 3:11 PM, Michael Hordijk <hoffbrinkle at hotmail.com> wrote: > > Using Clang/LLVM 3.6.0 we are observing a case where the optimizations are > clobbering EFLAGS on x86_64. This is inconvenient when the status of bit 9 > (IF), which controls interrupts, ch...

Using Clang/LLVM 3.6.0 we are observing a case where the optimizations are clobbering EFLAGS on x86_64. This is inconvenient when the status of bit 9 (IF), which controls interrupts, changes. Here's a simple test program. Assume that the external function foo() modifies the IF bit in EFLAGS. --- #include <stdlib.h> #include <stdbool.h> void foo(void); int a; int bar(void)