Avoid redundant pop/push before Throw/ReThrow in the flow-graph compiler.

vm/flow_graph_compiler_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/flow_graph_compiler.h"
 
 #include "lib/error.h"
@@ skipping 1268 matching lines @@
   __ nop(1);
   __ nop(1);
   AddCurrentDescriptor(PcDescriptors::kReturn,
                        instr->cid(),
                        instr->token_index(),
                        CatchClauseNode::kInvalidTryIndex);  // try-index.
 }
 
 
 void FlowGraphCompiler::VisitThrow(ThrowInstr* instr) {
-  LoadValue(RAX, instr->exception());
-  __ pushq(RAX);
+  ASSERT(instr->exception()->IsUse());
   GenerateCallRuntime(instr->cid(),
                       instr->token_index(),
                       instr->try_index(),
                       kThrowRuntimeEntry);
   __ int3();
 }
 
 
 void FlowGraphCompiler::VisitReThrow(ReThrowInstr* instr) {
-  LoadValue(RAX, instr->exception());
-  __ pushq(RAX);
-  LoadValue(RAX, instr->stack_trace());
-  __ pushq(RAX);
+  ASSERT(instr->exception()->IsUse());
+  ASSERT(instr->stack_trace()->IsUse());
   GenerateCallRuntime(instr->cid(),
                       instr->token_index(),
                       instr->try_index(),
                       kReThrowRuntimeEntry);
   __ int3();
 }
 
 
 
 void FlowGraphCompiler::VisitBranch(BranchInstr* instr) {
@@ skipping 441 matching lines @@
 
 
 void FlowGraphCompiler::FinalizeComments(const Code& code) {
   code.set_comments(assembler_->GetCodeComments());
 }
 
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_X64