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int x(int t) { if (t & 256) return -26; return 0; } We generate this: tst.w r0, #256 mvn r0, #25 it eq moveq r0, #0 while gcc generates this: ands r0, r0, #256 it ne mvnne r0, #25 bx lr Scandalous really! During ISel time, we can look for this particular pattern. One where we have a "MOVCC" that uses the flag off of a CMPZ that itself is comparing an AND instruction to 0. Something like this (greatly simplified): %r0 = ISD::AND ... ARMISD::CMPZ %r0, 0 @ sets [CPSR] %r0 = ARMISD::MOVCC 0, -26 @ reads [CPSR] All we have to do is convert the "ISD::AND" into an "ARM::ANDS" that sets [CPSR] when it's zero. The zero value will all ready be in the %r0 register and we only need to change it if the AND wasn't zero. Easy! git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@112664 91177308-0d34-0410-b5e6-96231b3b80d8 |
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