[TargetLowering][DAGCombine][MSP430] add/use hook for Shift Amount Threshold (1/2)

Provides a TLI hook to allow targets to relax the emission of shifts, thus enabling
codegen improvements on targets with no multiple shift instructions and cheap selects
or branches.

Contributes to a Fix for PR43559:
https://bugs.llvm.org/show_bug.cgi?id=43559

Patch by: @joanlluch (Joan LLuch)

Differential Revision: https://reviews.llvm.org/D69116

llvm-svn: 375347

1 files changed, 14 insertions, 12 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp b/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
index 0163ec35951..9ab1324533f 100644
--- a/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
@@ -3603,33 +3603,35 @@ SDValue TargetLowering::SimplifySetCC(EVT VT, SDValue N0, SDValue N1,
   // Back to non-vector simplifications.
   // TODO: Can we do these for vector splats?
   if (auto *N1C = dyn_cast<ConstantSDNode>(N1.getNode())) {
+    const TargetLowering &TLI = DAG.getTargetLoweringInfo();
     const APInt &C1 = N1C->getAPIntValue();
+    EVT ShValTy = N0.getValueType();
 
     // Fold bit comparisons when we can.
     if ((Cond == ISD::SETEQ || Cond == ISD::SETNE) &&
-        (VT == N0.getValueType() ||
-         (isTypeLegal(VT) && VT.bitsLE(N0.getValueType()))) &&
+        (VT == ShValTy || (isTypeLegal(VT) && VT.bitsLE(ShValTy))) &&
         N0.getOpcode() == ISD::AND) {
       auto &DL = DAG.getDataLayout();
       if (auto *AndRHS = dyn_cast<ConstantSDNode>(N0.getOperand(1))) {
-        EVT ShiftTy = getShiftAmountTy(N0.getValueType(), DL,
-                                       !DCI.isBeforeLegalize());
+        EVT ShiftTy = getShiftAmountTy(ShValTy, DL, !DCI.isBeforeLegalize());
         if (Cond == ISD::SETNE && C1 == 0) {// (X & 8) != 0  -->  (X & 8) >> 3
           // Perform the xform if the AND RHS is a single bit.
-          if (AndRHS->getAPIntValue().isPowerOf2()) {
+          unsigned ShCt = AndRHS->getAPIntValue().logBase2();
+          if (AndRHS->getAPIntValue().isPowerOf2() &&
+              ShCt <= TLI.getShiftAmountThreshold(ShValTy)) {
             return DAG.getNode(ISD::TRUNCATE, dl, VT,
-                              DAG.getNode(ISD::SRL, dl, N0.getValueType(), N0,
-                   DAG.getConstant(AndRHS->getAPIntValue().logBase2(), dl,
-                                   ShiftTy)));
+                               DAG.getNode(ISD::SRL, dl, ShValTy, N0,
+                                           DAG.getConstant(ShCt, dl, ShiftTy)));
           }
         } else if (Cond == ISD::SETEQ && C1 == AndRHS->getAPIntValue()) {
           // (X & 8) == 8  -->  (X & 8) >> 3
           // Perform the xform if C1 is a single bit.
-          if (C1.isPowerOf2()) {
+          unsigned ShCt = C1.logBase2();
+          if (C1.isPowerOf2() &&
+              ShCt <= TLI.getShiftAmountThreshold(ShValTy)) {
             return DAG.getNode(ISD::TRUNCATE, dl, VT,
-                               DAG.getNode(ISD::SRL, dl, N0.getValueType(), N0,
-                                      DAG.getConstant(C1.logBase2(), dl,
-                                                      ShiftTy)));
+                               DAG.getNode(ISD::SRL, dl, ShValTy, N0,
+                                           DAG.getConstant(ShCt, dl, ShiftTy)));
           }
         }
       }