diff options
Diffstat (limited to 'llvm/lib')
| -rw-r--r-- | llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp | 19 | ||||
| -rw-r--r-- | llvm/lib/Target/X86/X86ISelLowering.cpp | 4 |
2 files changed, 16 insertions, 7 deletions
diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp index 6d19f226a28..d09efca5e43 100644 --- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp +++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp @@ -2924,28 +2924,35 @@ SDValue DAGCombiner::visitMUL(SDNode *N) { } // Try to transform multiply-by-(power-of-2 +/- 1) into shift and add/sub. + // mul x, (2^N + 1) --> add (shl x, N), x + // mul x, (2^N - 1) --> sub (shl x, N), x // Examples: x * 33 --> (x << 5) + x // x * 15 --> (x << 4) - x + // x * -33 --> -((x << 5) + x) + // x * -15 --> -((x << 4) - x) ; this reduces --> x - (x << 4) if (N1IsConst && TLI.decomposeMulByConstant(VT, N1)) { - // TODO: Negative constants can be handled by negating the result. // TODO: We could handle more general decomposition of any constant by // having the target set a limit on number of ops and making a // callback to determine that sequence (similar to sqrt expansion). unsigned MathOp = ISD::DELETED_NODE; - if ((ConstValue1 - 1).isPowerOf2()) + APInt MulC = ConstValue1.abs(); + if ((MulC - 1).isPowerOf2()) MathOp = ISD::ADD; - else if ((ConstValue1 + 1).isPowerOf2()) + else if ((MulC + 1).isPowerOf2()) MathOp = ISD::SUB; if (MathOp != ISD::DELETED_NODE) { - unsigned ShAmt = MathOp == ISD::ADD ? (ConstValue1 - 1).logBase2() - : (ConstValue1 + 1).logBase2(); + unsigned ShAmt = MathOp == ISD::ADD ? (MulC - 1).logBase2() + : (MulC + 1).logBase2(); assert(ShAmt > 0 && ShAmt < VT.getScalarSizeInBits() && "Not expecting multiply-by-constant that could have simplified"); SDLoc DL(N); SDValue Shl = DAG.getNode(ISD::SHL, DL, VT, N0, DAG.getConstant(ShAmt, DL, VT)); - return DAG.getNode(MathOp, DL, VT, Shl, N0); + SDValue R = DAG.getNode(MathOp, DL, VT, Shl, N0); + if (ConstValue1.isNegative()) + R = DAG.getNode(ISD::SUB, DL, VT, DAG.getConstant(0, DL, VT), R); + return R; } } diff --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp index 398bf11065c..b49ef7b6a44 100644 --- a/llvm/lib/Target/X86/X86ISelLowering.cpp +++ b/llvm/lib/Target/X86/X86ISelLowering.cpp @@ -4736,7 +4736,9 @@ bool X86TargetLowering::decomposeMulByConstant(EVT VT, SDValue C) const { if (isOperationLegal(ISD::MUL, VT)) return false; - return (MulC + 1).isPowerOf2() || (MulC - 1).isPowerOf2(); + // shl+add, shl+sub, shl+add+neg + return (MulC + 1).isPowerOf2() || (MulC - 1).isPowerOf2() || + (1 - MulC).isPowerOf2() || (-(MulC + 1)).isPowerOf2(); } bool X86TargetLowering::isExtractSubvectorCheap(EVT ResVT, EVT SrcVT, |
