PPC: [turbofan] Add TruncationMode for TruncateFloat64ToInt32.

Port 4b38c158

Original commit message:
    We actually need round to zero truncation to implement the counterpart
    of LDoubleToI in TurboFan, which tries to convert a double to an integer
    as required for keyed load/store optimizations.

    Drive-by-cleanup: Reduce some code duplication in the InstructionSelector
    implementations.

R=bmeurer@chromium.org, dstence@us.ibm.com, michael_dawson@ca.ibm.com
BUG=

Review URL: https://codereview.chromium.org/1220373003

Cr-Commit-Position: refs/heads/master@{#29533}

src/compiler/ppc/instruction-selector-ppc.cc

@@ -874,26 +874,31 @@ void InstructionSelector::VisitChangeInt32ToInt64(Node* node) {
 
 void InstructionSelector::VisitChangeUint32ToUint64(Node* node) {
   // TODO(mbrandy): inspect input to see if nop is appropriate.
-  PPCOperandGenerator g(this);
-  Emit(kPPC_Uint32ToUint64, g.DefineAsRegister(node),
-       g.UseRegister(node->InputAt(0)));
+  VisitRR(this, kPPC_Uint32ToUint64, node);
 }
 #endif
 
 
 void InstructionSelector::VisitTruncateFloat64ToFloat32(Node* node) {
-  PPCOperandGenerator g(this);
-  Emit(kPPC_DoubleToFloat32, g.DefineAsRegister(node),
-       g.UseRegister(node->InputAt(0)));
+  VisitRR(this, kPPC_DoubleToFloat32, node);
+}
+
+
+void InstructionSelector::VisitTruncateFloat64ToInt32(Node* node) {
+  switch (TruncationModeOf(node->op())) {
+    case TruncationMode::kJavaScript:
+      return VisitRR(this, kArchTruncateDoubleToI, node);
+    case TruncationMode::kRoundToZero:
+      return VisitRR(this, kPPC_DoubleToInt32, node);
+  }
+  UNREACHABLE();
 }
 
 
 #if V8_TARGET_ARCH_PPC64
 void InstructionSelector::VisitTruncateInt64ToInt32(Node* node) {
-  PPCOperandGenerator g(this);
   // TODO(mbrandy): inspect input to see if nop is appropriate.
-  Emit(kPPC_Int64ToInt32, g.DefineAsRegister(node),
-       g.UseRegister(node->InputAt(0)));
+  VisitRR(this, kPPC_Int64ToInt32, node);
 }
 #endif