Use a special EnumLength field to indicate number of valid enum cache values.

src/ia32/full-codegen-ia32.cc

Index: src/ia32/full-codegen-ia32.cc
diff --git a/src/ia32/full-codegen-ia32.cc b/src/ia32/full-codegen-ia32.cc
index 75253c07a462c60b461e7d0d32498fc667870762..217a81e6f9dfb11bcc8e1db847dca75327959b5b 100644
--- a/src/ia32/full-codegen-ia32.cc
+++ b/src/ia32/full-codegen-ia32.cc
@@ -1089,18 +1089,29 @@ void FullCodeGenerator::VisitForInStatement(ForInStatement* stmt) {
 
   // We got a map in register eax. Get the enumeration cache from it.
   __ bind(&use_cache);
+
+  Label no_descriptors;

[Michael Starzinger, 2012/08/06 15:06:22]

Move this up above the __ bind() but below the comment. Also drop all the empty
newlines around the label. The label isn't the central thing here, the assembler
instructions are.

[Toon Verwaest, 2012/08/07 10:49:47]

Done.

+
+  __ EnumLength(edx, eax);
+  __ cmp(edx, Immediate(0));
+  __ j(equal, &no_descriptors);
+
   __ LoadInstanceDescriptors(eax, ecx);
   __ mov(ecx, FieldOperand(ecx, DescriptorArray::kEnumCacheOffset));
-  __ mov(edx, FieldOperand(ecx, DescriptorArray::kEnumCacheBridgeCacheOffset));
+  __ mov(ecx, FieldOperand(ecx, DescriptorArray::kEnumCacheBridgeCacheOffset));
 
   // Set up the four remaining stack slots.
   __ push(eax);  // Map.
-  __ push(edx);  // Enumeration cache.
-  __ mov(eax, FieldOperand(edx, FixedArray::kLengthOffset));
-  __ push(eax);  // Enumeration cache length (as smi).
+  __ push(ecx);  // Enumeration cache.
+  __ SmiTag(edx);
+  __ push(edx);  // Number of valid entries for the map in the enum cache.
   __ push(Immediate(Smi::FromInt(0)));  // Initial index.
   __ jmp(&loop);
 
+  __ bind(&no_descriptors);
+  __ add(esp, Immediate(kPointerSize));
+  __ jmp(&exit);
+
   // We got a fixed array in register eax. Iterate through that.
   Label non_proxy;
   __ bind(&fixed_array);