[x64] Optimize loading SMIs.

src/compiler/x64/instruction-selector-x64.cc

Index: src/compiler/x64/instruction-selector-x64.cc
diff --git a/src/compiler/x64/instruction-selector-x64.cc b/src/compiler/x64/instruction-selector-x64.cc
index edcf62a5ecbcd19db8a68d1a0c2abf08ecd508c9..282049e8130d3593894b001a160e7bb9b5fae300 100644
--- a/src/compiler/x64/instruction-selector-x64.cc
+++ b/src/compiler/x64/instruction-selector-x64.cc
@@ -63,6 +63,17 @@ class X64OperandGenerator final : public OperandGenerator {
     return false;
   }
 
+  AddressingMode EnsureHasDisplacement(
+      const BaseWithIndexAndDisplacement64Matcher& matcher,
+      AddressingMode mode) {
+    if (matcher.displacement() != nullptr) {
+      return mode;
+    }
+    DCHECK(mode == kMode_MR || (kMode_MR1 <= mode && mode <= kMode_MR8) ||

[Benedikt Meurer, 2016/04/01 08:33:00]

As discussed offline, please do a switch here. And please inline into the
callsite.

[epertoso, 2016/04/01 09:16:44]

Done.

+           (kMode_M4 == mode || kMode_M8 == mode));
+    return mode == kMode_MR ? kMode_MRI : static_cast<AddressingMode>(mode + 4);
+  }
+
   AddressingMode GenerateMemoryOperandInputs(Node* index, int scale_exponent,
                                              Node* base, Node* displacement,
                                              InstructionOperand inputs[],
@@ -618,6 +629,33 @@ void InstructionSelector::VisitWord32Sar(Node* node) {
 
 
 void InstructionSelector::VisitWord64Sar(Node* node) {
+  X64OperandGenerator g(this);
+  Int64BinopMatcher m(node);
+  if (CanCover(m.node(), m.left().node()) && m.left().IsLoad() &&
+      m.right().Is(32)) {
+    // Just load and sign-extend the interesting 4 bytes instead. This happens,
+    // for example, when we're loading and untagging SMIs.
+    BaseWithIndexAndDisplacement64Matcher mleft(m.left().node(), true);
+    if (mleft.matches() && (mleft.displacement() == nullptr ||
+                            g.CanBeImmediate(mleft.displacement()))) {
+      size_t input_count = 0;
+      InstructionOperand inputs[3];
+      AddressingMode mode = g.GetEffectiveAddressMemoryOperand(
+          m.left().node(), inputs, &input_count);
+      mode = g.EnsureHasDisplacement(mleft, mode);
+      if (mleft.displacement() == nullptr) {
+        inputs[input_count++] = ImmediateOperand(ImmediateOperand::INLINE, 4);
+      } else {
+        ImmediateOperand* op = ImmediateOperand::cast(&inputs[input_count - 1]);
+        int32_t displacement = sequence()->GetImmediate(op).ToInt32();
+        *op = ImmediateOperand(ImmediateOperand::INLINE, displacement + 4);
+      }
+      InstructionOperand outputs[] = {g.DefineAsRegister(node)};
+      InstructionCode code = kX64Movsxlq | AddressingModeField::encode(mode);
+      Emit(code, 1, outputs, input_count, inputs);
+      return;
+    }
+  }
   VisitWord64Shift(this, node, kX64Sar);
 }