ARM: Port r6635 and r6659

r6635: Remove the redundant load on every context lookup.
r6659: Do not compile the unreachable body of functions with illegal redeclarations.
Review URL: http://codereview.chromium.org/6572003

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@6920 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/arm/full-codegen-arm.cc

@@ -219,46 +219,47 @@ void FullCodeGenerator::Generate(CompilationInfo* info) {
     Move(dot_arguments_slot, r3, r1, r2);
   }
 
-  { Comment cmnt(masm_, "[ Declarations");
-    // For named function expressions, declare the function name as a
-    // constant.
-    if (scope()->is_function_scope() && scope()->function() != NULL) {
-      EmitDeclaration(scope()->function(), Variable::CONST, NULL);
-    }
-    // Visit all the explicit declarations unless there is an illegal
-    // redeclaration.
-    if (scope()->HasIllegalRedeclaration()) {
-      scope()->VisitIllegalRedeclaration(this);
-    } else {
-      VisitDeclarations(scope()->declarations());
-    }
-  }
-
   if (FLAG_trace) {
     __ CallRuntime(Runtime::kTraceEnter, 0);
   }
 
-  // Check the stack for overflow or break request.
-  { Comment cmnt(masm_, "[ Stack check");
-    PrepareForBailout(info->function(), NO_REGISTERS);
-    Label ok;
-    __ LoadRoot(ip, Heap::kStackLimitRootIndex);
-    __ cmp(sp, Operand(ip));
-    __ b(hs, &ok);
-    StackCheckStub stub;
-    __ CallStub(&stub);
-    __ bind(&ok);
-  }
+  // Visit the declarations and body unless there is an illegal
+  // redeclaration.
+  if (scope()->HasIllegalRedeclaration()) {
+    Comment cmnt(masm_, "[ Declarations");
+    scope()->VisitIllegalRedeclaration(this);
+
+  } else {
+    { Comment cmnt(masm_, "[ Declarations");
+      // For named function expressions, declare the function name as a
+      // constant.
+      if (scope()->is_function_scope() && scope()->function() != NULL) {
+        EmitDeclaration(scope()->function(), Variable::CONST, NULL);
+      }
+      VisitDeclarations(scope()->declarations());
+    }
 
-  { Comment cmnt(masm_, "[ Body");
-    ASSERT(loop_depth() == 0);
-    VisitStatements(function()->body());
-    ASSERT(loop_depth() == 0);
+    { Comment cmnt(masm_, "[ Stack check");
+      PrepareForBailout(info->function(), NO_REGISTERS);
+      Label ok;
+      __ LoadRoot(ip, Heap::kStackLimitRootIndex);
+      __ cmp(sp, Operand(ip));
+      __ b(hs, &ok);
+      StackCheckStub stub;
+      __ CallStub(&stub);
+      __ bind(&ok);
+    }
+
+    { Comment cmnt(masm_, "[ Body");
+      ASSERT(loop_depth() == 0);
+      VisitStatements(function()->body());
+      ASSERT(loop_depth() == 0);
+    }
   }
 
+  // Always emit a 'return undefined' in case control fell off the end of
+  // the body.
   { Comment cmnt(masm_, "[ return <undefined>;");
-    // Emit a 'return undefined' in case control fell off the end of the
-    // body.
     __ LoadRoot(r0, Heap::kUndefinedValueRootIndex);
   }
   EmitReturnSequence();
@@ -694,10 +695,11 @@ void FullCodeGenerator::EmitDeclaration(Variable* variable,
         // We bypass the general EmitSlotSearch because we know more about
         // this specific context.
 
-        // The variable in the decl always resides in the current context.
+        // The variable in the decl always resides in the current function
+        // context.
         ASSERT_EQ(0, scope()->ContextChainLength(variable->scope()));
         if (FLAG_debug_code) {
-          // Check if we have the correct context pointer.
+          // Check that we're not inside a 'with'.
           __ ldr(r1, ContextOperand(cp, Context::FCONTEXT_INDEX));
           __ cmp(r1, cp);
           __ Check(eq, "Unexpected declaration in current context.");
@@ -1037,7 +1039,7 @@ MemOperand FullCodeGenerator::ContextSlotOperandCheckExtensions(
     Slot* slot,
     Label* slow) {
   ASSERT(slot->type() == Slot::CONTEXT);
-  Register current = cp;
+  Register context = cp;
   Register next = r3;
   Register temp = r4;
 
@@ -1045,22 +1047,25 @@ MemOperand FullCodeGenerator::ContextSlotOperandCheckExtensions(
     if (s->num_heap_slots() > 0) {
       if (s->calls_eval()) {
         // Check that extension is NULL.
-        __ ldr(temp, ContextOperand(current, Context::EXTENSION_INDEX));
+        __ ldr(temp, ContextOperand(context, Context::EXTENSION_INDEX));
         __ tst(temp, temp);
         __ b(ne, slow);
       }
-      __ ldr(next, ContextOperand(current, Context::CLOSURE_INDEX));
+      __ ldr(next, ContextOperand(context, Context::CLOSURE_INDEX));
       __ ldr(next, FieldMemOperand(next, JSFunction::kContextOffset));
       // Walk the rest of the chain without clobbering cp.
-      current = next;
+      context = next;
     }
   }
   // Check that last extension is NULL.
-  __ ldr(temp, ContextOperand(current, Context::EXTENSION_INDEX));
+  __ ldr(temp, ContextOperand(context, Context::EXTENSION_INDEX));
   __ tst(temp, temp);
   __ b(ne, slow);
-  __ ldr(temp, ContextOperand(current, Context::FCONTEXT_INDEX));
-  return ContextOperand(temp, slot->index());
+
+  // This function is used only for loads, not stores, so it's safe to
+  // return an cp-based operand (the write barrier cannot be allowed to
+  // destroy the cp register).
+  return ContextOperand(context, slot->index());
 }
 
 
@@ -2004,34 +2009,60 @@ void FullCodeGenerator::EmitVariableAssignment(Variable* var,
         : Builtins::StoreIC_Initialize));
     EmitCallIC(ic, RelocInfo::CODE_TARGET_CONTEXT);
 
-  } else if (var->mode() != Variable::CONST || op == Token::INIT_CONST) {
-    // Perform the assignment for non-const variables and for initialization
-    // of const variables.  Const assignments are simply skipped.
-    Label done;
+  } else if (op == Token::INIT_CONST) {
+    // Like var declarations, const declarations are hoisted to function
+    // scope.  However, unlike var initializers, const initializers are able
+    // to drill a hole to that function context, even from inside a 'with'
+    // context.  We thus bypass the normal static scope lookup.
+    Slot* slot = var->AsSlot();
+    Label skip;
+    switch (slot->type()) {
+      case Slot::PARAMETER:
+        // No const parameters.
+        UNREACHABLE();
+        break;
+      case Slot::LOCAL:
+        // Detect const reinitialization by checking for the hole value.
+        __ ldr(r1, MemOperand(fp, SlotOffset(slot)));
+        __ LoadRoot(ip, Heap::kTheHoleValueRootIndex);
+        __ cmp(r1, ip);
+        __ b(ne, &skip);
+        __ str(result_register(), MemOperand(fp, SlotOffset(slot)));
+        break;
+      case Slot::CONTEXT: {
+        __ ldr(r1, ContextOperand(cp, Context::FCONTEXT_INDEX));
+        __ ldr(r2, ContextOperand(r1, slot->index()));
+        __ LoadRoot(ip, Heap::kTheHoleValueRootIndex);
+        __ cmp(r2, ip);
+        __ b(ne, &skip);
+        __ str(r0, ContextOperand(r1, slot->index()));
+        int offset = Context::SlotOffset(slot->index());
+        __ mov(r3, r0);  // Preserve the stored value in r0.
+        __ RecordWrite(r1, Operand(offset), r3, r2);
+        break;
+      }
+      case Slot::LOOKUP:
+        __ push(r0);
+        __ mov(r0, Operand(slot->var()->name()));
+        __ Push(cp, r0);  // Context and name.
+        __ CallRuntime(Runtime::kInitializeConstContextSlot, 3);
+        break;
+    }
+    __ bind(&skip);
+
+  } else if (var->mode() != Variable::CONST) {
+    // Perform the assignment for non-const variables.  Const assignments
+    // are simply skipped.
     Slot* slot = var->AsSlot();
     switch (slot->type()) {
       case Slot::PARAMETER:
       case Slot::LOCAL:
-        if (op == Token::INIT_CONST) {
-          // Detect const reinitialization by checking for the hole value.
-          __ ldr(r1, MemOperand(fp, SlotOffset(slot)));
-          __ LoadRoot(ip, Heap::kTheHoleValueRootIndex);
-          __ cmp(r1, ip);
-          __ b(ne, &done);
-        }
         // Perform the assignment.
         __ str(result_register(), MemOperand(fp, SlotOffset(slot)));
         break;
 
       case Slot::CONTEXT: {
         MemOperand target = EmitSlotSearch(slot, r1);
-        if (op == Token::INIT_CONST) {
-          // Detect const reinitialization by checking for the hole value.
-          __ ldr(r2, target);
-          __ LoadRoot(ip, Heap::kTheHoleValueRootIndex);
-          __ cmp(r2, ip);
-          __ b(ne, &done);
-        }
         // Perform the assignment and issue the write barrier.
         __ str(result_register(), target);
         // RecordWrite may destroy all its register arguments.
@@ -2042,20 +2073,13 @@ void FullCodeGenerator::EmitVariableAssignment(Variable* var,
       }
 
       case Slot::LOOKUP:
-        // Call the runtime for the assignment.  The runtime will ignore
-        // const reinitialization.
+        // Call the runtime for the assignment.
         __ push(r0);  // Value.
         __ mov(r0, Operand(slot->var()->name()));
         __ Push(cp, r0);  // Context and name.
-        if (op == Token::INIT_CONST) {
-          // The runtime will ignore const redeclaration.
-          __ CallRuntime(Runtime::kInitializeConstContextSlot, 3);
-        } else {
-          __ CallRuntime(Runtime::kStoreContextSlot, 3);
-        }
+        __ CallRuntime(Runtime::kStoreContextSlot, 3);
         break;
     }
-    __ bind(&done);
   }
 }
 

src/arm/lithium-arm.cc

@@ -1737,11 +1737,13 @@ LInstruction* LChunkBuilder::DoLoadContextSlot(HLoadContextSlot* instr) {
 
 
 LInstruction* LChunkBuilder::DoStoreContextSlot(HStoreContextSlot* instr) {
-  LOperand* context = UseTempRegister(instr->context());
+  LOperand* context;
   LOperand* value;
   if (instr->NeedsWriteBarrier()) {
+    context = UseTempRegister(instr->context());
     value = UseTempRegister(instr->value());
   } else {
+    context = UseRegister(instr->context());
     value = UseRegister(instr->value());
   }
   return new LStoreContextSlot(context, value);

src/arm/lithium-codegen-arm.cc

@@ -2112,17 +2112,13 @@ void LCodeGen::DoStoreGlobal(LStoreGlobal* instr) {
 void LCodeGen::DoLoadContextSlot(LLoadContextSlot* instr) {
   Register context = ToRegister(instr->context());
   Register result = ToRegister(instr->result());
-  __ ldr(result,
-         MemOperand(context, Context::SlotOffset(Context::FCONTEXT_INDEX)));
-  __ ldr(result, ContextOperand(result, instr->slot_index()));
+  __ ldr(result, ContextOperand(context, instr->slot_index()));
 }
 
 
 void LCodeGen::DoStoreContextSlot(LStoreContextSlot* instr) {
   Register context = ToRegister(instr->context());
   Register value = ToRegister(instr->value());
-  __ ldr(context,
-         MemOperand(context, Context::SlotOffset(Context::FCONTEXT_INDEX)));
   __ str(value, ContextOperand(context, instr->slot_index()));
   if (instr->needs_write_barrier()) {
     int offset = Context::SlotOffset(instr->slot_index());

src/arm/macro-assembler-arm.cc

@@ -2163,12 +2163,24 @@ void MacroAssembler::LoadContext(Register dst, int context_chain_length) {
       ldr(dst, MemOperand(dst, Context::SlotOffset(Context::CLOSURE_INDEX)));
       ldr(dst, FieldMemOperand(dst, JSFunction::kContextOffset));
     }
-    // The context may be an intermediate context, not a function context.
-    ldr(dst, MemOperand(dst, Context::SlotOffset(Context::FCONTEXT_INDEX)));
-  } else {  // Slot is in the current function context.
-    // The context may be an intermediate context, not a function context.
-    ldr(dst, MemOperand(cp, Context::SlotOffset(Context::FCONTEXT_INDEX)));
+  } else {
+    // Slot is in the current function context.  Move it into the
+    // destination register in case we store into it (the write barrier
+    // cannot be allowed to destroy the context in esi).
+    mov(dst, cp);
   }
+
+  // We should not have found a 'with' context by walking the context chain
+  // (i.e., the static scope chain and runtime context chain do not agree).
+  // A variable occurring in such a scope should have slot type LOOKUP and
+  // not CONTEXT.
+  if (FLAG_debug_code) {
+    ldr(ip, MemOperand(dst, Context::SlotOffset(Context::FCONTEXT_INDEX)));
+    cmp(dst, ip);
+    Check(eq, "Yo dawg, I heard you liked function contexts "
+              "so I put function contexts in all your contexts");
+  }
+
 }