24847a90aa
On targets without ADDCARRY or ADDE, we need to emit a separate SETCC to determine carry from the low half to the high half. The high half is calculated by a series of ADDs. When RHSLo and RHSHi are -1, without this patch, we get: Hi = (add (add LHSHi,(setult Lo, LHSLo), -1) Where as with the patch we get: Hi = (sub LHSHi, (seteq LHSLo, 0)) Only RHSLo is -1 we can instead do (setne Lo, 0). Similar to gcc: https://godbolt.org/z/M83f6rz39 Reviewed By: craig.topper Differential Revision: https://reviews.llvm.org/D146635
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