Enable GVN for polymorphic loads by not expanding them at the HIR level.

src/arm/lithium-codegen-arm.cc

Index: src/arm/lithium-codegen-arm.cc
===================================================================
--- src/arm/lithium-codegen-arm.cc	(revision 7299)
+++ src/arm/lithium-codegen-arm.cc	(working copy)
@@ -2175,6 +2175,72 @@
 }
 
 
+void LCodeGen::EmitLoadField(Register result,
+                             Register object,
+                             Handle<Map> type,
+                             Handle<String> name) {
+  LookupResult lookup;
+  type->LookupInDescriptors(NULL, *name, &lookup);
+  ASSERT(lookup.IsProperty() && lookup.type() == FIELD);
+  int index = lookup.GetLocalFieldIndexFromMap(*type);
+  int offset = index * kPointerSize;
+  if (index < 0) {
+    // Negative property indices are in-object properties, indexed
+    // from the end of the fixed part of the object.
+    __ ldr(result, FieldMemOperand(object, offset + type->instance_size()));
+  } else {
+    // Non-negative property indices are in the properties array.
+    __ ldr(result, FieldMemOperand(object, JSObject::kPropertiesOffset));
+    __ ldr(result, FieldMemOperand(result, offset + FixedArray::kHeaderSize));
+  }
+}
+
+
+void LCodeGen::DoLoadNamedFieldPolymorphic(LLoadNamedFieldPolymorphic* instr) {
+  Register object = ToRegister(instr->object());
+  Register result = ToRegister(instr->result());
+  Register scratch = scratch0();
+  int map_count = instr->hydrogen()->types()->length();
+  Handle<String> name = instr->hydrogen()->name();
+  if (map_count == 0) {
+    ASSERT(instr->hydrogen()->need_generic());
+    __ mov(r2, Operand(name));
+    Handle<Code> ic(
+        isolate()->builtins()->builtin(Builtins::LoadIC_Initialize));
+    CallCode(ic, RelocInfo::CODE_TARGET, instr);
+  } else {
+    Label done;
+    __ ldr(scratch, FieldMemOperand(object, HeapObject::kMapOffset));
+    for (int i = 0; i < map_count - 1; ++i) {
+      Handle<Map> map = instr->hydrogen()->types()->at(i);
+      Label next;
+      __ cmp(scratch, Operand(map));
+      __ b(ne, &next);
+      EmitLoadField(result, object, map, name);
+      __ b(&done);
+      __ bind(&next);
+    }
+    Handle<Map> map = instr->hydrogen()->types()->last();
+    __ cmp(scratch, Operand(map));
+    if (instr->hydrogen()->need_generic()) {
+      Label generic;
+      __ b(ne, &generic);
+      EmitLoadField(result, object, map, name);

[Kevin Millikin (Chromium), 2011/03/24 09:28:25]

BTW, you can write a single call to EmitLoadField by branching on eq and moving
EmitLoadField out of the if:

if (...) {
  Label load;
  __ b(eq, &load);
  // Call
  __ b(&done);
  __ bind(&load);
} else {
  DeoptimizeIf(...);
}
EmitLoadField(...);

It probably doesn't make much difference.

+      __ b(&done);
+      __ bind(&generic);
+      __ mov(r2, Operand(name));
+      Handle<Code> ic(
+          isolate()->builtins()->builtin(Builtins::LoadIC_Initialize));
+      CallCode(ic, RelocInfo::CODE_TARGET, instr);
+    } else {
+      DeoptimizeIf(ne, instr->environment());
+      EmitLoadField(result, object, map, name);
+    }
+    __ bind(&done);
+  }
+}
+
+
 void LCodeGen::DoLoadNamedGeneric(LLoadNamedGeneric* instr) {
   ASSERT(ToRegister(instr->object()).is(r0));
   ASSERT(ToRegister(instr->result()).is(r0));