Index: lib/CodeGen/SelectionDAG/SelectionDAG.cpp =================================================================== --- lib/CodeGen/SelectionDAG/SelectionDAG.cpp +++ lib/CodeGen/SelectionDAG/SelectionDAG.cpp @@ -2775,6 +2775,19 @@ return OFK_Never; } + // mulhi + 1 never overflow + if (N0.getOpcode() == ISD::UMUL_LOHI && N0.getResNo() == 1 && + (~N1Zero & 0x01) == ~N1Zero) + return OFK_Never; + + if (N1.getOpcode() == ISD::UMUL_LOHI && N1.getResNo() == 1) { + APInt N0Zero, N0One; + computeKnownBits(N0, N0Zero, N0One); + + if ((~N0Zero & 0x01) == ~N0Zero) + return OFK_Never; + } + return OFK_Sometime; } Index: test/CodeGen/X86/overflow.ll =================================================================== --- test/CodeGen/X86/overflow.ll +++ test/CodeGen/X86/overflow.ll @@ -35,12 +35,7 @@ ; ; X64-LABEL: mulhioverflow: ; X64: # BB#0: -; X64-NEXT: movq %rdx, %rcx -; X64-NEXT: movq %rdi, %rax -; X64-NEXT: mulq %rsi -; X64-NEXT: andl $1, %ecx -; X64-NEXT: addq %rdx, %rcx -; X64-NEXT: setb %al +; X64-NEXT: xorl %eax, %eax ; X64-NEXT: retq %1 = zext i64 %a to i128 %2 = zext i64 %b to i128