Displaying 1 result from an estimated 1 matches for "874b4633".
2015 Jan 22
2
[LLVMdev] X86TargetLowering::LowerToBT
That’s not how partial-flags update stalls work. There is no independent tracking of individual bits in EFLAGS. This means that BT + CMOVNZ has a false dependency on whatever instruction wrote to EFLAGS before BT and requires an extra µop vis-a-vis TEST + CMOVNZ or SHR + AND.
Please do not use BT. It is a performance hazard. If you don’t believe me for some reason, here’s the relevant quote