Change __ mov(eax, TOS) to

__ pop(eax);
...
__ push(eax);
to enable push/pop eliminations.

__ push(eax) must happen before RecordWrite because RecordWrite may destroy 
eax value. To be safe, also moved __ push(r0) on ARM to above RecordWrite.

This only affects the case where a context variable is used in a inner scope.

Create a tests for it. It fails if __ push(eax) is after RecordWrite.



git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@111 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/codegen-arm.cc

@@ -3238,6 +3238,7 @@ void ArmCodeGenerator::VisitSlot(Slot* node) {
         // r2 may be loaded with context; used below in RecordWrite.
         __ pop(r0);
         __ str(r0, SlotOperand(node, r2));
+        __ push(r0);
         if (node->type() == Slot::CONTEXT) {
           // Skip write barrier if the written value is a smi.
           Label exit;
@@ -3249,7 +3250,6 @@ void ArmCodeGenerator::VisitSlot(Slot* node) {
           __ RecordWrite(r2, r3, r1);
           __ bind(&exit);
         }
-        __ push(r0);
         break;
       }
     }

src/codegen-ia32.cc

@@ -3440,8 +3440,9 @@ void Ia32CodeGenerator::VisitSlot(Slot* node) {
         // Variable::CONST because of const declarations which will
         // initialize consts to 'the hole' value and by doing so, end
         // up calling this code.
-        __ mov(eax, TOS);
+        __ pop(eax);
         __ mov(SlotOperand(node, ecx), eax);
+        __ push(eax);  // RecordWrite may destroy the value in eax.
         if (node->type() == Slot::CONTEXT) {
           // ecx is loaded with context when calling SlotOperand above.
           int offset = FixedArray::kHeaderSize + node->index() * kPointerSize;

test/mjsunit/context-variable-assignments.js

@@ -0,0 +1,37 @@
+// Copyright 2008 Google Inc. All Rights Reserved.
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+//       notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+//       copyright notice, this list of conditions and the following
+//       disclaimer in the documentation and/or other materials provided
+//       with the distribution.
+//     * Neither the name of Google Inc. nor the names of its
+//       contributors may be used to endorse or promote products derived
+//       from this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+function foo() {
+  var a, b;
+  var bar = function() {
+    a = b = "hello world";
+  }
+  bar();
+  return a;
+}
+
+assertEquals("hello world", foo());