Add support to load/store byte fields.

src/ia32/lithium-codegen-ia32.cc

Index: src/ia32/lithium-codegen-ia32.cc
diff --git a/src/ia32/lithium-codegen-ia32.cc b/src/ia32/lithium-codegen-ia32.cc
index 14d16c018e0f8ceac3cf0ddaa1646bb06f4e48db..3662d21c04772572c30f9f428cb2e685626c1ee7 100644
--- a/src/ia32/lithium-codegen-ia32.cc
+++ b/src/ia32/lithium-codegen-ia32.cc
@@ -3225,12 +3225,15 @@ void LCodeGen::DoLoadNamedField(LLoadNamedField* instr) {
 
   if (access.IsExternalMemory()) {
     Register result = ToRegister(instr->result());
-    if (instr->object()->IsConstantOperand()) {
-      ExternalReference external_reference = ToExternalReference(
-          LConstantOperand::cast(instr->object()));
-      __ mov(result, MemOperand::StaticVariable(external_reference));
+    MemOperand operand = instr->object()->IsConstantOperand()
+        ? MemOperand::StaticVariable(ToExternalReference(
+                LConstantOperand::cast(instr->object())))
+        : MemOperand(ToRegister(instr->object()), offset);
+    if (access.representation().IsByte()) {
+      ASSERT(instr->hydrogen()->representation().IsInteger32());
+      __ movzx_b(result, operand);
     } else {
-      __ mov(result, MemOperand(ToRegister(instr->object()), offset));
+      __ mov(result, operand);
     }
     return;
   }
@@ -3249,11 +3252,15 @@ void LCodeGen::DoLoadNamedField(LLoadNamedField* instr) {
   }
 
   Register result = ToRegister(instr->result());
-  if (access.IsInobject()) {
-    __ mov(result, FieldOperand(object, offset));
-  } else {
+  if (!access.IsInobject()) {
     __ mov(result, FieldOperand(object, JSObject::kPropertiesOffset));
-    __ mov(result, FieldOperand(result, offset));
+    object = result;
+  }
+  if (access.representation().IsByte()) {
+    ASSERT(instr->hydrogen()->representation().IsInteger32());
+    __ movzx_b(result, FieldOperand(object, offset));
+  } else {
+    __ mov(result, FieldOperand(object, offset));
   }
 }
 
@@ -4429,10 +4436,18 @@ void LCodeGen::DoStoreNamedField(LStoreNamedField* instr) {
         : MemOperand(ToRegister(instr->object()), offset);
     if (instr->value()->IsConstantOperand()) {
       LConstantOperand* operand_value = LConstantOperand::cast(instr->value());
-      __ mov(operand, Immediate(ToInteger32(operand_value)));
+      if (representation.IsByte()) {
+        __ mov_b(operand, ToInteger32(operand_value));

[Jakob Kummerow, 2013/10/02 16:25:42]

Here you're passing an int32_t to a function that expects an int8_t. I'm
surprised this even compiles on Windows.

[Benedikt Meurer, 2013/10/04 07:14:53]

It simply truncates to int8_t according to implicit type conversion rules. Just
what we want here.

+      } else {
+        __ mov(operand, Immediate(ToInteger32(operand_value)));
+      }
     } else {
       Register value = ToRegister(instr->value());
-      __ mov(operand, value);
+      if (representation.IsByte()) {
+        __ mov_b(operand, value);

[Jakob Kummerow, 2013/10/02 16:25:42]

This will fail the CHECK in mov_b when the register allocator happens to pick,
say, edi for |value|. If you had added a test case, you would have noticed ;-)

Same thing twice more below.

[Benedikt Meurer, 2013/10/04 07:14:53]

Good catch, thanks.

+      } else {
+        __ mov(operand, value);
+      }
     }
     return;
   }
@@ -4505,17 +4520,28 @@ void LCodeGen::DoStoreNamedField(LStoreNamedField* instr) {
     __ mov(write_register, FieldOperand(object, JSObject::kPropertiesOffset));
   }
 
+  MemOperand operand = FieldOperand(write_register, offset);
   if (instr->value()->IsConstantOperand()) {
     LConstantOperand* operand_value = LConstantOperand::cast(instr->value());
     if (operand_value->IsRegister()) {
-      __ mov(FieldOperand(write_register, offset), ToRegister(operand_value));
+      Register value = ToRegister(operand_value);
+      if (representation.IsByte()) {
+        __ mov_b(operand, value);
+      } else {
+        __ mov(operand, value);
+      }
     } else {
       Handle<Object> handle_value = ToHandle(operand_value);
       ASSERT(!instr->hydrogen()->NeedsWriteBarrier());
-      __ mov(FieldOperand(write_register, offset), handle_value);
+      __ mov(operand, handle_value);
     }
   } else {
-    __ mov(FieldOperand(write_register, offset), ToRegister(instr->value()));
+    Register value = ToRegister(instr->value());
+    if (representation.IsByte()) {
+      __ mov_b(operand, value);
+    } else {
+      __ mov(operand, value);
+    }
   }
 
   if (instr->hydrogen()->NeedsWriteBarrier()) {