Out-of-line constant pool on Arm: Stage 1 - Free up r7 for use as constant pool pointer register

src/arm/builtins-arm.cc

 // Copyright 2012 the V8 project authors. 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
@@ skipping 442 matching lines @@
       __ str(r6, MemOperand(r5, kPointerSize, PostIndex));
       ASSERT_EQ(2 * kPointerSize, JSObject::kElementsOffset);
       __ str(r6, MemOperand(r5, kPointerSize, PostIndex));
 
       // Fill all the in-object properties with the appropriate filler.
       // r1: constructor function
       // r2: initial map
       // r3: object size (in words)
       // r4: JSObject (not tagged)
       // r5: First in-object property of JSObject (not tagged)
-      __ add(r6, r4, Operand(r3, LSL, kPointerSizeLog2));  // End of object.
       ASSERT_EQ(3 * kPointerSize, JSObject::kHeaderSize);
-      __ LoadRoot(r7, Heap::kUndefinedValueRootIndex);
+      __ LoadRoot(r6, Heap::kUndefinedValueRootIndex);
       if (count_constructions) {
         __ ldr(r0, FieldMemOperand(r2, Map::kInstanceSizesOffset));
         __ Ubfx(r0, r0, Map::kPreAllocatedPropertyFieldsByte * kBitsPerByte,
                 kBitsPerByte);
         __ add(r0, r5, Operand(r0, LSL, kPointerSizeLog2));
         // r0: offset of first field after pre-allocated fields
         if (FLAG_debug_code) {
-          __ cmp(r0, r6);
+          __ add(ip, r4, Operand(r3, LSL, kPointerSizeLog2));  // End of object.
+          __ cmp(r0, ip);
           __ Assert(le, "Unexpected number of pre-allocated property fields.");
         }
-        __ InitializeFieldsWithFiller(r5, r0, r7);
+        __ InitializeFieldsWithFiller(r5, r0, r6);
         // To allow for truncation.
-        __ LoadRoot(r7, Heap::kOnePointerFillerMapRootIndex);
+        __ LoadRoot(r6, Heap::kOnePointerFillerMapRootIndex);
       }
-      __ InitializeFieldsWithFiller(r5, r6, r7);
+      __ add(r0, r4, Operand(r3, LSL, kPointerSizeLog2));  // End of object.
+      __ InitializeFieldsWithFiller(r5, r0, r6);
 
       // Add the object tag to make the JSObject real, so that we can continue
       // and jump into the continuation code at any time from now on. Any
       // failures need to undo the allocation, so that the heap is in a
       // consistent state and verifiable.
       __ add(r4, r4, Operand(kHeapObjectTag));
 
       // Check if a non-empty properties array is needed. Continue with
       // allocated object if not fall through to runtime call if it is.
       // r1: constructor function
@@ skipping 44 matching lines @@
 
       // Initialize the fields to undefined.
       // r1: constructor function
       // r2: First element of FixedArray (not tagged)
       // r3: number of elements in properties array
       // r4: JSObject
       // r5: FixedArray (not tagged)
       __ add(r6, r2, Operand(r3, LSL, kPointerSizeLog2));  // End of object.
       ASSERT_EQ(2 * kPointerSize, FixedArray::kHeaderSize);
       { Label loop, entry;
-        if (count_constructions) {
-          __ LoadRoot(r7, Heap::kUndefinedValueRootIndex);
-        } else if (FLAG_debug_code) {
-          __ LoadRoot(r8, Heap::kUndefinedValueRootIndex);
-          __ cmp(r7, r8);
-          __ Assert(eq, "Undefined value not loaded.");
-        }

[JF, 2013/07/29 17:20:09]

I'm not sure I understand this change.

[rmcilroy, 2013/07/30 11:39:44]

Beforehand, the code would only reloaded r7 with Heap::kUndefinedValueRootIndex
if count_constructors was true, otherwise it would already hold
Heap::kUndefinedValueRootIndex from l465 (The debug code seems to be checking
that r7 hasn't been clobbered between these lines).  Now, 
I have to reload Heap::kUndefinedValueRootIndex unconditionally (since I load it
into r6 above, and r6 is clobbered in between).  Therefore, there is no need for
the conditional on count_constructions or the debug code to check that the reg
wasn't clobbered.

+        __ LoadRoot(r0, Heap::kUndefinedValueRootIndex);
         __ b(&entry);
         __ bind(&loop);
-        __ str(r7, MemOperand(r2, kPointerSize, PostIndex));
+        __ str(r0, MemOperand(r2, kPointerSize, PostIndex));
         __ bind(&entry);
         __ cmp(r2, r6);
         __ b(lt, &loop);
       }
 
       // Store the initialized FixedArray into the properties field of
       // the JSObject
       // r1: constructor function
       // r4: JSObject
       // r5: FixedArray (not tagged)
@@ skipping 143 matching lines @@
 
 
 static void Generate_JSEntryTrampolineHelper(MacroAssembler* masm,
                                              bool is_construct) {
   // Called from Generate_JS_Entry
   // r0: code entry
   // r1: function
   // r2: receiver
   // r3: argc
   // r4: argv
-  // r5-r7, cp may be clobbered
+  // r5-r6, cp may be clobbered

[JF, 2013/07/29 17:20:09]

r7 can still be clobbered if the flag doesn't sequester it.

[rmcilroy, 2013/07/30 11:39:44]

Done.

   ProfileEntryHookStub::MaybeCallEntryHook(masm);
 
   // Clear the context before we push it when entering the internal frame.
   __ mov(cp, Operand::Zero());
 
   // Enter an internal frame.
   {
     FrameScope scope(masm, StackFrame::INTERNAL);
 
     // Set up the context from the function argument.
@@ skipping 19 matching lines @@
     __ push(r0);  // push parameter
     __ bind(&entry);
     __ cmp(r4, r2);
     __ b(ne, &loop);
 
     // Initialize all JavaScript callee-saved registers, since they will be seen
     // by the garbage collector as part of handlers.
     __ LoadRoot(r4, Heap::kUndefinedValueRootIndex);
     __ mov(r5, Operand(r4));
     __ mov(r6, Operand(r4));
-    __ mov(r7, Operand(r4));

[JF, 2013/07/29 17:20:09]

This should be conditional on the flag being enabled not, otherwise it may look
like a GC root.

[rmcilroy, 2013/07/30 11:39:44]

Done.

     if (kR9Available == 1) {
       __ mov(r9, Operand(r4));
     }
 
     // Invoke the code and pass argc as r0.
     __ mov(r0, Operand(r3));
     if (is_construct) {
       // No type feedback cell is available
       Handle<Object> undefined_sentinel(
           masm->isolate()->heap()->undefined_value(), masm->isolate());
@@ skipping 706 matching lines @@
   __ bind(&dont_adapt_arguments);
   __ Jump(r3);
 }
 
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_ARM