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

src/arm/builtins-arm.cc

Index: src/arm/builtins-arm.cc
diff --git a/src/arm/builtins-arm.cc b/src/arm/builtins-arm.cc
index eff47e2692bfc2627f4e4269da609b030d39367d..0581a12ec209ea81e18ceff2fd1146608e7d99e9 100644
--- a/src/arm/builtins-arm.cc
+++ b/src/arm/builtins-arm.cc
@@ -460,9 +460,8 @@ static void Generate_JSConstructStubHelper(MacroAssembler* masm,
       // 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,
@@ -470,14 +469,16 @@ static void Generate_JSConstructStubHelper(MacroAssembler* masm,
         __ 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
@@ -542,16 +543,10 @@ static void Generate_JSConstructStubHelper(MacroAssembler* masm,
       __ 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);
@@ -715,7 +710,7 @@ static void Generate_JSEntryTrampolineHelper(MacroAssembler* masm,
   // 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.
@@ -755,7 +750,6 @@ static void Generate_JSEntryTrampolineHelper(MacroAssembler* masm,
     __ 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));
     }