Make register allocator to disregard constant computation with no uses.

runtime/vm/intermediate_language_x64.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/globals.h"  // Needed here to get TARGET_ARCH_X64.
 #if defined(TARGET_ARCH_X64)
 
 #include "vm/intermediate_language.h"
 
 #include "lib/error.h"
@@ skipping 156 matching lines @@
 
 
 LocationSummary* ConstantComp::MakeLocationSummary() const {
   return LocationSummary::Make(0,
                                Location::RequiresRegister(),
                                LocationSummary::kNoCall);
 }
 
 
 void ConstantComp::EmitNativeCode(FlowGraphCompiler* compiler) {
-  Register result = locs()->out().reg();
-  __ LoadObject(result, value());
+  // Register allocator drops constant definitions that have no uses.
+  if (!locs()->out().IsInvalid()) {
+    Register result = locs()->out().reg();
+    __ LoadObject(result, value());
+  }
 }
 
 
 LocationSummary* AssertAssignableComp::MakeLocationSummary() const {
   const intptr_t kNumInputs = 3;
   const intptr_t kNumTemps = 0;
   LocationSummary* summary =
       new LocationSummary(kNumInputs, kNumTemps, LocationSummary::kCall);
   summary->set_in(0, Location::RegisterLocation(RAX));  // Value.
   summary->set_in(1, Location::RegisterLocation(RCX));  // Instantiator.
@@ skipping 1253 matching lines @@
 
   Register temp = locs()->temp(0).reg();
   // Generate stack overflow check.
   __ movq(temp, Immediate(Isolate::Current()->stack_limit_address()));
   __ cmpq(RSP, Address(temp, 0));
   __ j(BELOW_EQUAL, slow_path->entry_label());
   __ Bind(slow_path->exit_label());
 }
 
 
+static bool CanBeImmediate(const Object& constant) {
+  return constant.IsSmi() &&
+    Immediate(reinterpret_cast<int64_t>(constant.raw())).is_int32();
+}
+
 LocationSummary* BinarySmiOpComp::MakeLocationSummary() const {
   const intptr_t kNumInputs = 2;
+
+  ConstantComp* right_constant = right()->definition()->AsConstant();
+  if ((right_constant != NULL) &&
+      (op_kind() != Token::kTRUNCDIV) &&
+      (op_kind() != Token::kSHL) &&
+      (op_kind() != Token::kMUL) &&
+      CanBeImmediate(right_constant->value())) {
+    const intptr_t kNumTemps = 0;
+    LocationSummary* summary =
+        new LocationSummary(kNumInputs, kNumTemps, LocationSummary::kNoCall);
+    summary->set_in(0, Location::RequiresRegister());
+    summary->set_in(1, Location::Constant(right_constant->value()));
+    summary->set_out(Location::SameAsFirstInput());
+    return summary;
+  }
+
   if (op_kind() == Token::kTRUNCDIV) {
     const intptr_t kNumTemps = 3;
     LocationSummary* summary =
         new LocationSummary(kNumInputs, kNumTemps, LocationSummary::kNoCall);
     summary->set_in(0, Location::RegisterLocation(RAX));
     summary->set_in(1, Location::RegisterLocation(RCX));
     summary->set_out(Location::SameAsFirstInput());
     summary->set_temp(0, Location::RegisterLocation(RBX));
     // Will be used for for sign extension.
     summary->set_temp(1, Location::RegisterLocation(RDX));
@@ skipping 25 matching lines @@
     summary->set_in(0, Location::RequiresRegister());
     summary->set_in(1, Location::RequiresRegister());
     summary->set_out(Location::SameAsFirstInput());
     return summary;
   }
 }
 
 
 void BinarySmiOpComp::EmitNativeCode(FlowGraphCompiler* compiler) {
   Register left = locs()->in(0).reg();
-  Register right = locs()->in(1).reg();
   Register result = locs()->out().reg();
   ASSERT(left == result);
   Label* deopt = NULL;
   switch (op_kind()) {
     case Token::kBIT_AND:
     case Token::kBIT_OR:
     case Token::kBIT_XOR:
       // Can't deoptimize. Arguments are already checked for smi.
       break;
     default:
       deopt = compiler->AddDeoptStub(instance_call()->deopt_id(),
                                      kDeoptBinarySmiOp);
   }
+
+  if (locs()->in(1).IsConstant()) {
+    const Object& constant = locs()->in(1).constant();
+    ASSERT(constant.IsSmi());
+    const int64_t imm =
+        reinterpret_cast<int64_t>(constant.raw());
+    switch (op_kind()) {
+      case Token::kADD: {
+        __ addq(left, Immediate(imm));
+        __ j(OVERFLOW, deopt);
+        break;
+      }
+      case Token::kSUB: {
+        __ subq(left, Immediate(imm));
+        __ j(OVERFLOW, deopt);
+        break;
+      }
+      case Token::kBIT_AND: {
+        // No overflow check.
+        __ andq(left, Immediate(imm));
+        break;
+      }
+      case Token::kBIT_OR: {
+        // No overflow check.
+        __ orq(left, Immediate(imm));
+        break;
+      }
+      case Token::kBIT_XOR: {
+        // No overflow check.
+        __ xorq(left, Immediate(imm));
+        break;
+      }
+
+      case Token::kSHR: {
+        // sarq operation masks the count to 6 bits.
+        const intptr_t kCountLimit = 0x3F;
+        intptr_t value = Smi::Cast(constant).Value();
+
+        if (value == 0) {
+          // TODO(vegorov): should be handled outside.
+          break;
+        } else if (value < 0) {
+          // TODO(vegorov): should be handled outside.
+          __ jmp(deopt);
+          break;
+        }
+
+        value = value + kSmiTagSize;
+        if (value >= kCountLimit) value = kCountLimit;
+
+        __ sarq(left, Immediate(value));
+        __ SmiTag(left);
+        break;
+      }
+      default:
+        UNREACHABLE();
+        break;
+    }
+    return;
+  }
+
+  Register right = locs()->in(1).reg();
   switch (op_kind()) {
     case Token::kADD: {
       __ addq(left, right);
       __ j(OVERFLOW, deopt);
       break;
     }
     case Token::kSUB: {
       __ subq(left, right);
       __ j(OVERFLOW, deopt);
       break;
@@ skipping 675 matching lines @@
   }
   __ j(ABOVE_EQUAL, deopt);
 }
 
 
 }  // namespace dart
 
 #undef __
 
 #endif  // defined TARGET_ARCH_X64