Index: llvm/lib/Target/AArch64/AArch64InstrInfo.cpp =================================================================== --- llvm/lib/Target/AArch64/AArch64InstrInfo.cpp +++ llvm/lib/Target/AArch64/AArch64InstrInfo.cpp @@ -1692,17 +1692,23 @@ /// MI and CmpInstr /// or if MI opcode is not the S form there must be neither defs of flags /// nor uses of flags between MI and CmpInstr. -/// - and C/V flags are not used after CmpInstr +/// - and C flag is not used after CmpInstr static bool canInstrSubstituteCmpInstr(MachineInstr &MI, MachineInstr &CmpInstr, const TargetRegisterInfo &TRI) { + // NOTE this assertion guarantees that MI.getOpcode() is the S-form of add or + // subtraction. assert(sForm(MI) != AArch64::INSTRUCTION_LIST_END); const unsigned CmpOpcode = CmpInstr.getOpcode(); if (!isADDSRegImm(CmpOpcode) && !isSUBSRegImm(CmpOpcode)) return false; + assert((CmpInstr.getOperand(2).isImm() && + CmpInstr.getOperand(2).getImm() == 0) && + "Caller guarantees that CmpInstr compares with constant 0"); + std::optional NZVCUsed = examineCFlagsUse(MI, CmpInstr, TRI); - if (!NZVCUsed || NZVCUsed->C || NZVCUsed->V) + if (!NZVCUsed || NZVCUsed->C) return false; AccessKind AccessToCheck = AK_Write; Index: llvm/test/CodeGen/AArch64/aarch64-icmp-opt.ll =================================================================== --- llvm/test/CodeGen/AArch64/aarch64-icmp-opt.ll +++ llvm/test/CodeGen/AArch64/aarch64-icmp-opt.ll @@ -7,8 +7,7 @@ define i32 @sub_icmp_i32(i32 %0, i32 %1) { ; CHECK-LABEL: sub_icmp_i32: ; CHECK: // %bb.0: -; CHECK-NEXT: sub w0, w0, w1 -; CHECK-NEXT: cmp w0, #0 +; CHECK-NEXT: subs w0, w0, w1 ; CHECK-NEXT: b.le .LBB0_2 ; CHECK-NEXT: // %bb.1: ; CHECK-NEXT: b _Z2f2i @@ -36,8 +35,7 @@ define i64 @sub_icmp_i64(i64 %0, i64 %1) { ; CHECK-LABEL: sub_icmp_i64: ; CHECK: // %bb.0: -; CHECK-NEXT: sub x0, x0, x1 -; CHECK-NEXT: cmp x0, #0 +; CHECK-NEXT: subs x0, x0, x1 ; CHECK-NEXT: b.le .LBB1_2 ; CHECK-NEXT: // %bb.1: ; CHECK-NEXT: b _Z2f4l @@ -63,8 +61,7 @@ define i64 @add_i64(i64 %0, i64 %1) { ; CHECK-LABEL: add_i64: ; CHECK: // %bb.0: -; CHECK-NEXT: add x0, x1, x0 -; CHECK-NEXT: cmp x0, #0 +; CHECK-NEXT: adds x0, x1, x0 ; CHECK-NEXT: b.le .LBB2_2 ; CHECK-NEXT: // %bb.1: ; CHECK-NEXT: b _Z2f4l @@ -90,8 +87,7 @@ define i32 @add_i32(i32 %0, i32 %1) { ; CHECK-LABEL: add_i32: ; CHECK: // %bb.0: -; CHECK-NEXT: add w0, w1, w0 -; CHECK-NEXT: cmp w0, #0 +; CHECK-NEXT: adds w0, w1, w0 ; CHECK-NEXT: b.le .LBB3_2 ; CHECK-NEXT: // %bb.1: ; CHECK-NEXT: b _Z2f4l Index: llvm/test/CodeGen/AArch64/arm64-csel.ll =================================================================== --- llvm/test/CodeGen/AArch64/arm64-csel.ll +++ llvm/test/CodeGen/AArch64/arm64-csel.ll @@ -79,8 +79,7 @@ define i32@foo6(i32 %a, i32 %b) nounwind ssp { ; CHECK-LABEL: foo6: ; CHECK: // %bb.0: // %common.ret -; CHECK-NEXT: sub w8, w0, w1 -; CHECK-NEXT: cmp w8, #0 +; CHECK-NEXT: subs w8, w0, w1 ; CHECK-NEXT: csinc w0, w8, wzr, le ; CHECK-NEXT: ret %sub = sub nsw i32 %a, %b