diff --git a/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp b/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp index ac545534d728b..5b9e699eaa408 100644 --- a/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp +++ b/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp @@ -3392,8 +3392,19 @@ bool isLegalCmpImmed(APInt C) { return isLegalArithImmed(C.abs().getZExtValue()); } -static bool cannotBeIntMin(SDValue CheckedVal, SelectionDAG &DAG) { - KnownBits KnownSrc = DAG.computeKnownBits(CheckedVal); +static bool isSafeSignedCMN(SDValue Op, SelectionDAG &DAG) { + // 0 - INT_MIN sign wraps, so no signed wrap means cmn is safe. + if (Op->getFlags().hasNoSignedWrap()) + return true; + + // We can still figure out if the second operand is safe to use + // in a CMN instruction by checking if it is known to be not the minimum + // signed value. If it is not, then we can safely use CMN. + // Note: We can eventually remove this check and simply rely on + // Op->getFlags().hasNoSignedWrap() once SelectionDAG/ISelLowering + // consistently sets them appropriately when making said nodes. + + KnownBits KnownSrc = DAG.computeKnownBits(Op.getOperand(1)); return !KnownSrc.getSignedMinValue().isMinSignedValue(); } @@ -3402,7 +3413,7 @@ static bool cannotBeIntMin(SDValue CheckedVal, SelectionDAG &DAG) { // can be set differently by this operation. It comes down to whether // "SInt(~op2)+1 == SInt(~op2+1)" (and the same for UInt). If they are then // everything is fine. If not then the optimization is wrong. Thus general -// comparisons are only valid if op2 != 0. +// comparisons are only valid if op2 != 0 and op2 != INT_MIN. // // So, finally, the only LLVM-native comparisons that don't mention C or V // are the ones that aren't unsigned comparisons. They're the only ones we can @@ -3411,7 +3422,7 @@ static bool isCMN(SDValue Op, ISD::CondCode CC, SelectionDAG &DAG) { return Op.getOpcode() == ISD::SUB && isNullConstant(Op.getOperand(0)) && (isIntEqualitySetCC(CC) || (isUnsignedIntSetCC(CC) && DAG.isKnownNeverZero(Op.getOperand(1))) || - (isSignedIntSetCC(CC) && cannotBeIntMin(Op.getOperand(1), DAG))); + (isSignedIntSetCC(CC) && isSafeSignedCMN(Op, DAG))); } static SDValue emitStrictFPComparison(SDValue LHS, SDValue RHS, const SDLoc &dl, diff --git a/llvm/test/CodeGen/AArch64/cmp-to-cmn.ll b/llvm/test/CodeGen/AArch64/cmp-to-cmn.ll index c5fd9b63cce97..5765e0acae269 100644 --- a/llvm/test/CodeGen/AArch64/cmp-to-cmn.ll +++ b/llvm/test/CodeGen/AArch64/cmp-to-cmn.ll @@ -602,3 +602,49 @@ define i1 @almost_immediate_neg_ugt_64(i64 %x) { %cmp = icmp ugt i64 %x, -16773121 ret i1 %cmp } + +define i1 @cmn_nsw(i32 %a, i32 %b) { +; CHECK-LABEL: cmn_nsw: +; CHECK: // %bb.0: +; CHECK-NEXT: cmn w0, w1 +; CHECK-NEXT: cset w0, gt +; CHECK-NEXT: ret + %sub = sub nsw i32 0, %b + %cmp = icmp sgt i32 %a, %sub + ret i1 %cmp +} + +define i1 @cmn_nsw_64(i64 %a, i64 %b) { +; CHECK-LABEL: cmn_nsw_64: +; CHECK: // %bb.0: +; CHECK-NEXT: cmn x0, x1 +; CHECK-NEXT: cset w0, gt +; CHECK-NEXT: ret + %sub = sub nsw i64 0, %b + %cmp = icmp sgt i64 %a, %sub + ret i1 %cmp +} + +define i1 @cmn_nsw_neg(i32 %a, i32 %b) { +; CHECK-LABEL: cmn_nsw_neg: +; CHECK: // %bb.0: +; CHECK-NEXT: neg w8, w1 +; CHECK-NEXT: cmp w0, w8 +; CHECK-NEXT: cset w0, gt +; CHECK-NEXT: ret + %sub = sub i32 0, %b + %cmp = icmp sgt i32 %a, %sub + ret i1 %cmp +} + +define i1 @cmn_nsw_neg_64(i64 %a, i64 %b) { +; CHECK-LABEL: cmn_nsw_neg_64: +; CHECK: // %bb.0: +; CHECK-NEXT: neg x8, x1 +; CHECK-NEXT: cmp x0, x8 +; CHECK-NEXT: cset w0, gt +; CHECK-NEXT: ret + %sub = sub i64 0, %b + %cmp = icmp sgt i64 %a, %sub + ret i1 %cmp +}