CCed Jakub,
> Hi Alex, > Agree that float division don't touch memory ,but fdiv result (stack > register ) is stored back to a memory i.e fResult . > > So compiler barrier in the inline asm i.e ::memory should prevent the > shrinkage of instructions like "fstps fResult(%rip)" behind the > fence ? > > BTW ,if we make fDivident and fResult = 0.0f gloabls,the code > emitted looks ok i.e > #gcc -S test.c -O3 -mmmx -mno-sse > > flds .LC0(%rip) > fsts fDivident(%rip) > fdivs .LC1(%rip) > fstps fResult(%rip) > #APP > # 10 "test.c" 1 > mfence > # 0 "" 2 > #NO_APP > flds fResult(%rip) > movl $.LC2, %edi > xorl %eax, %eax > fstpl (%rsp) > call printf > > So i strongly believe that ,its compiler issue and please feel free > correct me in any case. > > Thank you and waiting for your reply. > > ~Umesh > > > > > On Fri, Apr 13, 2018 at 5:58 PM, Alexander Monakov <amona...@ispras.ru> wrote: >> On Fri, 13 Apr 2018, Vivek Kinhekar wrote: >>> The mfence instruction with memory clobber asm instruction should create a >>> barrier between division and printf instructions. >> >> No, floating-point division does not touch memory, so the asm does not (and >> need not) restrict its motion. >> >> Alexander
