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

src/arm/codegen-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 407 matching lines @@
                       OMIT_SMI_CHECK);
 }
 
 
 void ElementsTransitionGenerator::GenerateSmiToDouble(
     MacroAssembler* masm, AllocationSiteMode mode, Label* fail) {
   // ----------- S t a t e -------------
   //  -- r0    : value
   //  -- r1    : key
   //  -- r2    : receiver
-  //  -- lr    : return address
+  //  -- lr    : rturn address
   //  -- r3    : target map, scratch for subsequent call
   //  -- r4    : scratch (elements)
   // -----------------------------------
   Label loop, entry, convert_hole, gc_required, only_change_map, done;
 
   if (mode == TRACK_ALLOCATION_SITE) {
     __ TestJSArrayForAllocationMemento(r2, r4);
     __ b(eq, fail);
   }
 
   // Check for empty arrays, which only require a map transition and no changes
   // to the backing store.
   __ ldr(r4, FieldMemOperand(r2, JSObject::kElementsOffset));
   __ CompareRoot(r4, Heap::kEmptyFixedArrayRootIndex);
   __ b(eq, &only_change_map);
 
   __ push(lr);
   __ ldr(r5, FieldMemOperand(r4, FixedArray::kLengthOffset));
-  // r4: source FixedArray
   // r5: number of elements (smi-tagged)
 
   // Allocate new FixedDoubleArray.
   // Use lr as a temporary register.
   __ mov(lr, Operand(r5, LSL, 2));
   __ add(lr, lr, Operand(FixedDoubleArray::kHeaderSize));
-  __ Allocate(lr, r6, r7, r9, &gc_required, DOUBLE_ALIGNMENT);
+  __ Allocate(lr, r6, r4, r9, &gc_required, DOUBLE_ALIGNMENT);
   // r6: destination FixedDoubleArray, not tagged as heap object.
 
   // Set destination FixedDoubleArray's length and map.
   __ LoadRoot(r9, Heap::kFixedDoubleArrayMapRootIndex);
   __ str(r5, MemOperand(r6, FixedDoubleArray::kLengthOffset));
   // Update receiver's map.
   __ str(r9, MemOperand(r6, HeapObject::kMapOffset));
 
   __ str(r3, FieldMemOperand(r2, HeapObject::kMapOffset));
   __ RecordWriteField(r2,
@@ skipping 10 matching lines @@
   __ RecordWriteField(r2,
                       JSObject::kElementsOffset,
                       r3,
                       r9,
                       kLRHasBeenSaved,
                       kDontSaveFPRegs,
                       EMIT_REMEMBERED_SET,
                       OMIT_SMI_CHECK);
 
   // Prepare for conversion loop.
+  __ ldr(r4, FieldMemOperand(r2, JSObject::kElementsOffset));

[ulan, 2013/09/13 13:58:22]

FieldMemOperand(r2, JSObject::kElementsOffset) is overwritten above in line 473.

[rmcilroy_google, 2013/09/13 14:52:58]

Ahh, you're right, nice spot!  Fixed by moving up. 

   __ add(r3, r4, Operand(FixedArray::kHeaderSize - kHeapObjectTag));
-  __ add(r7, r6, Operand(FixedDoubleArray::kHeaderSize));
-  __ add(r6, r7, Operand(r5, LSL, 2));
+  __ add(r9, r6, Operand(FixedDoubleArray::kHeaderSize));
+  __ add(r6, r9, Operand(r5, LSL, 2));
   __ mov(r4, Operand(kHoleNanLower32));
   __ mov(r5, Operand(kHoleNanUpper32));
   // r3: begin of source FixedArray element fields, not tagged
   // r4: kHoleNanLower32
   // r5: kHoleNanUpper32
   // r6: end of destination FixedDoubleArray, not tagged
-  // r7: begin of FixedDoubleArray element fields, not tagged
+  // r9: begin of FixedDoubleArray element fields, not tagged
 
   __ b(&entry);
 
   __ bind(&only_change_map);
   __ str(r3, FieldMemOperand(r2, HeapObject::kMapOffset));
   __ RecordWriteField(r2,
                       HeapObject::kMapOffset,
                       r3,
                       r9,

[ulan, 2013/09/13 12:06:27]

This can clobber r9, so the use below seems to be invalid.

[rmcilroy_google, 2013/09/13 12:16:44]

But this is never called on the same codepath as below (L496 never falls through
since it's an unconditional branch, so the only entry point to "only_change_map"
is the branch on L443, and the code block immediately branches to "done" on
L508, so it never hits the use of r9 from L486-L494 and L516-L540).

                       kLRHasNotBeenSaved,
                       kDontSaveFPRegs,
                       OMIT_REMEMBERED_SET,
                       OMIT_SMI_CHECK);
   __ b(&done);
 
   // Call into runtime if GC is required.
   __ bind(&gc_required);
   __ pop(lr);
   __ b(fail);
 
   // Convert and copy elements.
   __ bind(&loop);
-  __ ldr(r9, MemOperand(r3, 4, PostIndex));
-  // r9: current element
-  __ UntagAndJumpIfNotSmi(r9, r9, &convert_hole);
+  __ ldr(lr, MemOperand(r3, 4, PostIndex));
+  // lr: current element
+  __ UntagAndJumpIfNotSmi(lr, lr, &convert_hole);
 
   // Normal smi, convert to double and store.
-  __ vmov(s0, r9);
+  __ vmov(s0, lr);
   __ vcvt_f64_s32(d0, s0);
-  __ vstr(d0, r7, 0);
-  __ add(r7, r7, Operand(8));
+  __ vstr(d0, r9, 0);
+  __ add(r9, r9, Operand(8));
   __ b(&entry);
 
   // Hole found, store the-hole NaN.
   __ bind(&convert_hole);
   if (FLAG_debug_code) {
     // Restore a "smi-untagged" heap object.
-    __ SmiTag(r9);
-    __ orr(r9, r9, Operand(1));
-    __ CompareRoot(r9, Heap::kTheHoleValueRootIndex);
+    __ SmiTag(lr);
+    __ orr(lr, lr, Operand(1));
+    __ CompareRoot(lr, Heap::kTheHoleValueRootIndex);
     __ Assert(eq, kObjectFoundInSmiOnlyArray);
   }
-  __ Strd(r4, r5, MemOperand(r7, 8, PostIndex));
+  __ Strd(r4, r5, MemOperand(r9, 8, PostIndex));
 
   __ bind(&entry);
-  __ cmp(r7, r6);
+  __ cmp(r9, r6);
   __ b(lt, &loop);
 
   __ pop(lr);
   __ bind(&done);
 }
 
 
 void ElementsTransitionGenerator::GenerateDoubleToObject(
     MacroAssembler* masm, AllocationSiteMode mode, Label* fail) {
   // ----------- S t a t e -------------
@@ skipping 19 matching lines @@
 
   __ push(lr);
   __ Push(r3, r2, r1, r0);
   __ ldr(r5, FieldMemOperand(r4, FixedArray::kLengthOffset));
   // r4: source FixedDoubleArray
   // r5: number of elements (smi-tagged)
 
   // Allocate new FixedArray.
   __ mov(r0, Operand(FixedDoubleArray::kHeaderSize));
   __ add(r0, r0, Operand(r5, LSL, 1));
-  __ Allocate(r0, r6, r7, r9, &gc_required, NO_ALLOCATION_FLAGS);
+  __ Allocate(r0, r6, r3, r9, &gc_required, NO_ALLOCATION_FLAGS);
   // r6: destination FixedArray, not tagged as heap object
   // Set destination FixedDoubleArray's length and map.
   __ LoadRoot(r9, Heap::kFixedArrayMapRootIndex);
   __ str(r5, MemOperand(r6, FixedDoubleArray::kLengthOffset));
   __ str(r9, MemOperand(r6, HeapObject::kMapOffset));
 
   // Prepare for conversion loop.
   __ add(r4, r4, Operand(FixedDoubleArray::kHeaderSize - kHeapObjectTag + 4));
   __ add(r3, r6, Operand(FixedArray::kHeaderSize));
   __ add(r6, r6, Operand(kHeapObjectTag));
   __ add(r5, r3, Operand(r5, LSL, 1));
-  __ LoadRoot(r7, Heap::kTheHoleValueRootIndex);
   __ LoadRoot(r9, Heap::kHeapNumberMapRootIndex);
   // Using offsetted addresses in r4 to fully take advantage of post-indexing.
   // r3: begin of destination FixedArray element fields, not tagged
   // r4: begin of source FixedDoubleArray element fields, not tagged, +4
   // r5: end of destination FixedArray, not tagged
   // r6: destination FixedArray
-  // r7: the-hole pointer
   // r9: heap number map
   __ b(&entry);
 
   // Call into runtime if GC is required.
   __ bind(&gc_required);
   __ Pop(r3, r2, r1, r0);
   __ pop(lr);
   __ b(fail);
 
   __ bind(&loop);
   __ ldr(r1, MemOperand(r4, 8, PostIndex));
-  // lr: current element's upper 32 bit
+  // r1: current element's upper 32 bit
   // r4: address of next element's upper 32 bit
   __ cmp(r1, Operand(kHoleNanUpper32));
   __ b(eq, &convert_hole);
 
   // Non-hole double, copy value into a heap number.
   __ AllocateHeapNumber(r2, r0, lr, r9, &gc_required);
   // r2: new heap number
   __ ldr(r0, MemOperand(r4, 12, NegOffset));
   __ Strd(r0, r1, FieldMemOperand(r2, HeapNumber::kValueOffset));
   __ mov(r0, r3);
   __ str(r2, MemOperand(r3, 4, PostIndex));
   __ RecordWrite(r6,
                  r0,
                  r2,
                  kLRHasBeenSaved,
                  kDontSaveFPRegs,
                  EMIT_REMEMBERED_SET,
                  OMIT_SMI_CHECK);
   __ b(&entry);
 
   // Replace the-hole NaN with the-hole pointer.
   __ bind(&convert_hole);
-  __ str(r7, MemOperand(r3, 4, PostIndex));
+  __ LoadRoot(r0, Heap::kTheHoleValueRootIndex);
+  __ str(r0, MemOperand(r3, 4, PostIndex));
 
   __ bind(&entry);
   __ cmp(r3, r5);
   __ b(lt, &loop);
 
   __ Pop(r3, r2, r1, r0);
   // Replace receiver's backing store with newly created and filled FixedArray.
   __ str(r6, FieldMemOperand(r2, JSObject::kElementsOffset));
   __ RecordWriteField(r2,
                       JSObject::kElementsOffset,
@@ skipping 239 matching lines @@
     patcher.masm()->add(r0, pc, Operand(-8));
     patcher.masm()->ldr(pc, MemOperand(pc, -4));
     patcher.masm()->dd(reinterpret_cast<uint32_t>(stub->instruction_start()));
   }
 }
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_ARM