PPC: Support immediate indices for StoreWriteBarrier.

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

Index: src/compiler/ppc/instruction-selector-ppc.cc
diff --git a/src/compiler/ppc/instruction-selector-ppc.cc b/src/compiler/ppc/instruction-selector-ppc.cc
index d3de14bf55d76c7fec6b9b3e0eaf7a6cfc10a1e5..ba6e2372bb679a76e949bfb64c53196b34fa23f2 100644
--- a/src/compiler/ppc/instruction-selector-ppc.cc
+++ b/src/compiler/ppc/instruction-selector-ppc.cc
@@ -227,13 +227,25 @@ void InstructionSelector::VisitStore(Node* node) {
   WriteBarrierKind write_barrier_kind = store_rep.write_barrier_kind();
   MachineRepresentation rep = store_rep.representation();
 
-  // TODO(ppc): I guess this could be done in a better way.
   if (write_barrier_kind != kNoWriteBarrier) {
     DCHECK_EQ(MachineRepresentation::kTagged, rep);
+    AddressingMode addressing_mode;
     InstructionOperand inputs[3];
     size_t input_count = 0;
     inputs[input_count++] = g.UseUniqueRegister(base);
-    inputs[input_count++] = g.UseUniqueRegister(offset);
+    // OutOfLineRecordWrite uses the offset in an 'add' instruction as well as
+    // for the store itself, so we must check compatibility with both.
+    if (g.CanBeImmediate(offset, kInt16Imm)
+#if V8_TARGET_ARCH_PPC64
+        && g.CanBeImmediate(offset, kInt16Imm_4ByteAligned)
+#endif
+            ) {
+      inputs[input_count++] = g.UseImmediate(offset);
+      addressing_mode = kMode_MRI;
+    } else {
+      inputs[input_count++] = g.UseUniqueRegister(offset);
+      addressing_mode = kMode_MRR;
+    }
     inputs[input_count++] = (write_barrier_kind == kMapWriteBarrier)
                                 ? g.UseRegister(value)
                                 : g.UseUniqueRegister(value);
@@ -255,6 +267,7 @@ void InstructionSelector::VisitStore(Node* node) {
     InstructionOperand temps[] = {g.TempRegister(), g.TempRegister()};
     size_t const temp_count = arraysize(temps);
     InstructionCode code = kArchStoreWithWriteBarrier;
+    code |= AddressingModeField::encode(addressing_mode);
     code |= MiscField::encode(static_cast<int>(record_write_mode));
     Emit(code, 0, nullptr, input_count, inputs, temp_count, temps);
   } else {