MIPS64: Port '[ARM64] Optimize load followed by shift.'

src/compiler/mips64/instruction-selector-mips64.cc

Index: src/compiler/mips64/instruction-selector-mips64.cc
diff --git a/src/compiler/mips64/instruction-selector-mips64.cc b/src/compiler/mips64/instruction-selector-mips64.cc
index 1b3b6a6d62ccfc598253072bb32c7c83934f145a..6f72c6451d1fb920c0aae444f7cf1dbeb3ff6182 100644
--- a/src/compiler/mips64/instruction-selector-mips64.cc
+++ b/src/compiler/mips64/instruction-selector-mips64.cc
@@ -31,14 +31,25 @@ class Mips64OperandGenerator final : public OperandGenerator {
     return UseRegister(node);
   }
 
-  bool CanBeImmediate(Node* node, InstructionCode opcode) {
-    int64_t value;
-    if (node->opcode() == IrOpcode::kInt32Constant)
-      value = OpParameter<int32_t>(node);
-    else if (node->opcode() == IrOpcode::kInt64Constant)
-      value = OpParameter<int64_t>(node);
-    else
-      return false;
+  bool IsIntegerConstant(Node* node) {
+    return (node->opcode() == IrOpcode::kInt32Constant) ||
+           (node->opcode() == IrOpcode::kInt64Constant);
+  }
+
+  int64_t GetIntegerConstantValue(Node* node) {
+    if (node->opcode() == IrOpcode::kInt32Constant) {
+      return OpParameter<int32_t>(node);
+    }
+    DCHECK(node->opcode() == IrOpcode::kInt64Constant);
+    return OpParameter<int64_t>(node);
+  }
+
+  bool CanBeImmediate(Node* node, InstructionCode mode) {
+    return IsIntegerConstant(node) &&
+           CanBeImmediate(GetIntegerConstantValue(node), mode);
+  }
+
+  bool CanBeImmediate(int64_t value, InstructionCode opcode) {
     switch (ArchOpcodeField::decode(opcode)) {
       case kMips64Shl:
       case kMips64Sar:
@@ -91,6 +102,76 @@ static void VisitRRO(InstructionSelector* selector, ArchOpcode opcode,
                  g.UseOperand(node->InputAt(1), opcode));
 }
 
+struct ExtendingLoadMatcher {
+  ExtendingLoadMatcher(Node* node, InstructionSelector* selector)
+      : matches_(false), selector_(selector), base_(nullptr), immediate_(0) {
+    Initialize(node);
+  }
+
+  bool Matches() const { return matches_; }
+
+  Node* base() const {
+    DCHECK(Matches());
+    return base_;
+  }
+  int64_t immediate() const {
+    DCHECK(Matches());
+    return immediate_;
+  }
+  ArchOpcode opcode() const {
+    DCHECK(Matches());
+    return opcode_;
+  }
+
+ private:
+  bool matches_;
+  InstructionSelector* selector_;
+  Node* base_;
+  int64_t immediate_;
+  ArchOpcode opcode_;
+
+  void Initialize(Node* node) {
+    Int64BinopMatcher m(node);
+    // When loading a 64-bit value and shifting by 32, we should
+    // just load and sign-extend the interesting 4 bytes instead.
+    // This happens, for example, when we're loading and untagging SMIs.
+    DCHECK(m.IsWord64Sar());
+    if (m.left().IsLoad() && m.right().Is(32) &&
+        selector_->CanCover(m.node(), m.left().node())) {
+      Mips64OperandGenerator g(selector_);
+      Node* load = m.left().node();
+      Node* offset = load->InputAt(1);
+      base_ = load->InputAt(0);
+      opcode_ = kMips64Lw;
+      if (g.CanBeImmediate(offset, opcode_)) {
+#if defined(V8_TARGET_LITTLE_ENDIAN)
+        immediate_ = g.GetIntegerConstantValue(offset) + 4;
+#elif defined(V8_TARGET_BIG_ENDIAN)
+        immediate_ = g.GetIntegerConstantValue(offset);
+#endif
+        matches_ = g.CanBeImmediate(immediate_, kMips64Lw);
+      }
+    }
+  }
+};
+
+bool TryEmitExtendingLoad(InstructionSelector* selector, Node* node) {
+  ExtendingLoadMatcher m(node, selector);
+  Mips64OperandGenerator g(selector);
+  if (m.Matches()) {
+    InstructionOperand inputs[2];
+    inputs[0] = g.UseRegister(m.base());
+    InstructionCode opcode =
+        m.opcode() | AddressingModeField::encode(kMode_MRI);
+    DCHECK(is_int32(m.immediate()));
+    inputs[1] = g.TempImmediate(static_cast<int32_t>(m.immediate()));
+    InstructionOperand outputs[] = {g.DefineAsRegister(node)};
+    selector->Emit(opcode, arraysize(outputs), outputs, arraysize(inputs),
+                   inputs);
+    return true;
+  }
+  return false;
+}
 
 static void VisitBinop(InstructionSelector* selector, Node* node,
                        InstructionCode opcode, FlagsContinuation* cont) {
@@ -597,6 +678,7 @@ void InstructionSelector::VisitWord64Shr(Node* node) {
 
 
 void InstructionSelector::VisitWord64Sar(Node* node) {
+  if (TryEmitExtendingLoad(this, node)) return;
   VisitRRO(this, kMips64Dsar, node);
 }