Some cheap DAG combine goodness for multiplication with a particular constant.
This can be extended later on to handle more "complex" constants.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@103881 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Target/ARM/ARMISelLowering.cpp b/lib/Target/ARM/ARMISelLowering.cpp
index 49dd951..1e415d1 100644
--- a/lib/Target/ARM/ARMISelLowering.cpp
+++ b/lib/Target/ARM/ARMISelLowering.cpp
@@ -463,6 +463,7 @@
// ARMISD::VMOVRRD - No need to call setTargetDAGCombine
setTargetDAGCombine(ISD::ADD);
setTargetDAGCombine(ISD::SUB);
+ setTargetDAGCombine(ISD::MUL);
setStackPointerRegisterToSaveRestore(ARM::SP);
setSchedulingPreference(SchedulingForRegPressure);
@@ -3584,6 +3585,75 @@
return SDValue();
}
+static SDValue PerformMULCombine(SDNode *N,
+ TargetLowering::DAGCombinerInfo &DCI,
+ const ARMSubtarget *Subtarget) {
+ SelectionDAG &DAG = DCI.DAG;
+
+ if (Subtarget->isThumb1Only())
+ return SDValue();
+
+ if (DAG.getMachineFunction().
+ getFunction()->hasFnAttr(Attribute::OptimizeForSize))
+ return SDValue();
+
+ if (DCI.isBeforeLegalize() || DCI.isCalledByLegalizer())
+ return SDValue();
+
+ EVT VT = N->getValueType(0);
+ if (VT != MVT::i32)
+ return SDValue();
+
+ ConstantSDNode *C = dyn_cast<ConstantSDNode>(N->getOperand(1));
+ if (!C)
+ return SDValue();
+
+ uint64_t MulAmt = C->getZExtValue();
+ unsigned ShiftAmt = CountTrailingZeros_64(MulAmt);
+ ShiftAmt = ShiftAmt & (32 - 1);
+ SDValue V = N->getOperand(0);
+ DebugLoc DL = N->getDebugLoc();
+ SDValue NewAdd;
+
+ // FIXME: Handle arbitrary powers of 2.
+ switch (MulAmt >> ShiftAmt) {
+ case 3: // 2 + 1
+ NewAdd = DAG.getNode(ISD::ADD, DL, VT,
+ V, DAG.getNode(ISD::SHL, DL, VT,
+ V, DAG.getConstant(1, MVT::i32)));
+ break;
+ case 5: // 4 + 1
+ NewAdd = DAG.getNode(ISD::ADD, DL, VT,
+ V, DAG.getNode(ISD::SHL, DL, VT,
+ V, DAG.getConstant(2, MVT::i32)));
+ break;
+ case 7: // 8 - 1
+ NewAdd = DAG.getNode(ISD::SUB, DL, VT,
+ DAG.getNode(ISD::SHL, DL, VT,
+ V, DAG.getConstant(3, MVT::i32)),
+ V);
+ break;
+ case 9: // 8 + 1
+ NewAdd = DAG.getNode(ISD::ADD, DL, VT,
+ V, DAG.getNode(ISD::SHL, DL, VT,
+ V, DAG.getConstant(3, MVT::i32)));
+ break;
+ default: return SDValue();
+ }
+
+ if (ShiftAmt != 0) {
+ SDValue NewShift = DAG.getNode(ISD::SHL, DL, VT, NewAdd,
+ DAG.getConstant(ShiftAmt, MVT::i32));
+ // Do not add new nodes to DAG combiner worklist.
+ DCI.CombineTo(N, NewShift, false);
+ return SDValue();
+ }
+
+ // Do not add new nodes to DAG combiner worklist.
+ DCI.CombineTo(N, NewAdd, false);
+ return SDValue();
+}
+
/// PerformVMOVRRDCombine - Target-specific dag combine xforms for
/// ARMISD::VMOVRRD.
static SDValue PerformVMOVRRDCombine(SDNode *N,
@@ -3970,6 +4040,7 @@
default: break;
case ISD::ADD: return PerformADDCombine(N, DCI);
case ISD::SUB: return PerformSUBCombine(N, DCI);
+ case ISD::MUL: return PerformMULCombine(N, DCI, Subtarget);
case ARMISD::VMOVRRD: return PerformVMOVRRDCombine(N, DCI);
case ISD::INTRINSIC_WO_CHAIN: return PerformIntrinsicCombine(N, DCI.DAG);
case ISD::SHL: