search for: kmovb

...: %r1 = and <4 x i1> %r0, <i1 -1, i1 -1, i1 -1, i1 -1> At the IR level the all1s mask looks like the Identity for this operation, so LLVM will remove it. But it is not the Identity since this operation should clear the top 4 bits of the 8 bit hardware register in play. E.g. kmovb -4(%rsp), %k0 kandb %k0, %k1, %k0 kmovb %k0, -4(%rsp) I began tracking down this issue and found that InstCombine will incorrectly remove the AND. Then I noticed that the Reassociate pass would also remove the AND if InstCombine did not. That made me nervous. My current think...

...will remove it. But it is not the Identity since >> this operation should clear the top 4 bits of the 8 bit hardware >> register in play. E.g. > > No, this operation alone does not need to clear the upper bit, they are undefined before and after. > > >> >> kmovb -4(%rsp), %k0 >> kandb %k0, %k1, %k0 >> kmovb %k0, -4(%rsp) >> >> I began tracking down this issue and found that InstCombine will >> incorrectly remove the AND. Then I noticed that the Reassociate pass >> would also remove the AND if InstComb...

...dentity since >>>> this operation should clear the top 4 bits of the 8 bit hardware >>>> register in play. E.g. >>> No, this operation alone does not need to clear the upper bit, they are undefined before and after. >>> >>> >>>> kmovb -4(%rsp), %k0 >>>> kandb %k0, %k1, %k0 >>>> kmovb %k0, -4(%rsp) >>>> >>>> I began tracking down this issue and found that InstCombine will >>>> incorrectly remove the AND. Then I noticed that the Reassociate pass >...