[DAG] Add TLI::isTruncateFree(SDValue, EVT) wrapper.

Similar to the existing isZExtFree(SDValue, EVT) wrapper, this will allow targets to override for specific cases (e.g. free truncation of an ext/extload node). But for now its just used to wrap the existing isTruncateFree(EVT, EVT) call.

Author: RKSimon

llvm/include/llvm/CodeGen/TargetLowering.h

@@ -2869,6 +2869,12 @@ class TargetLoweringBase {
                           getApproximateEVTForLLT(ToTy, DL, Ctx));
   }
 
+  /// Return true if truncating the specific node Val to type VT2 is free.
+  virtual bool isTruncateFree(SDValue Val, EVT VT2) const {
+    // Fallback to type matching.
+    return isTruncateFree(Val.getValueType(), VT2);
+  }
+
   virtual bool isProfitableToHoist(Instruction *I) const { return true; }
 
   /// Return true if the extension represented by \p I is free.

llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

@@ -13703,8 +13703,7 @@ SDValue DAGCombiner::visitZERO_EXTEND(SDNode *N) {
   if (N0.getOpcode() == ISD::AND &&
       N0.getOperand(0).getOpcode() == ISD::TRUNCATE &&
       N0.getOperand(1).getOpcode() == ISD::Constant &&
-      (!TLI.isTruncateFree(N0.getOperand(0).getOperand(0).getValueType(),
-                           N0.getValueType()) ||
+      (!TLI.isTruncateFree(N0.getOperand(0).getOperand(0), N0.getValueType()) ||
        !TLI.isZExtFree(N0.getValueType(), VT))) {
     SDValue X = N0.getOperand(0).getOperand(0);
     X = DAG.getAnyExtOrTrunc(X, SDLoc(X), VT);
@@ -13935,8 +13934,7 @@ SDValue DAGCombiner::visitANY_EXTEND(SDNode *N) {
   if (N0.getOpcode() == ISD::AND &&
       N0.getOperand(0).getOpcode() == ISD::TRUNCATE &&
       N0.getOperand(1).getOpcode() == ISD::Constant &&
-      !TLI.isTruncateFree(N0.getOperand(0).getOperand(0).getValueType(),
-                          N0.getValueType())) {
+      !TLI.isTruncateFree(N0.getOperand(0).getOperand(0), N0.getValueType())) {
     SDLoc DL(N);
     SDValue X = DAG.getAnyExtOrTrunc(N0.getOperand(0).getOperand(0), DL, VT);
     SDValue Y = DAG.getNode(ISD::ANY_EXTEND, DL, VT, N0.getOperand(1));
@@ -18855,8 +18853,7 @@ struct LoadedSlice {
     void addSliceGain(const LoadedSlice &LS) {
       // Each slice saves a truncate.
       const TargetLowering &TLI = LS.DAG->getTargetLoweringInfo();
-      if (!TLI.isTruncateFree(LS.Inst->getOperand(0).getValueType(),
-                              LS.Inst->getValueType(0)))
+      if (!TLI.isTruncateFree(LS.Inst->getOperand(0), LS.Inst->getValueType(0)))
         ++Truncates;
       // If there is a shift amount, this slice gets rid of it.
       if (LS.Shift)