InstCombine: Turn icmp + sext into bitwise/integer ops when the input has only one unknown bit.
int test1(unsigned x) { return (x&8) ? 0 : -1; }
int test3(unsigned x) { return (x&8) ? -1 : 0; }
before (x86_64):
_test1:
andl $8, %edi
cmpl $1, %edi
sbbl %eax, %eax
ret
_test3:
andl $8, %edi
cmpl $1, %edi
sbbl %eax, %eax
notl %eax
ret
after:
_test1:
shrl $3, %edi
andl $1, %edi
leal -1(%rdi), %eax
ret
_test3:
shll $28, %edi
movl %edi, %eax
sarl $31, %eax
ret
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@128732
91177308-0d34-0410-b5e6-
96231b3b80d8