MIPS: Fix uninitialized FixedArray potentially being left behind by ElementsTransitionGenerator::Ge…

src/mips/codegen-mips.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/v8.h"
 
 #if V8_TARGET_ARCH_MIPS
 
 #include "src/codegen.h"
 #include "src/macro-assembler.h"
@@ skipping 878 matching lines @@
 
   // Prepare for conversion loop.
   Register src_elements = elements;
   Register dst_elements = target_map;
   Register dst_end = length;
   Register heap_number_map = scratch;
   __ Addu(src_elements, src_elements, Operand(
         FixedDoubleArray::kHeaderSize - kHeapObjectTag
         + Register::kExponentOffset));
   __ Addu(dst_elements, array, Operand(FixedArray::kHeaderSize));
-  __ Addu(array, array, Operand(kHeapObjectTag));
   __ sll(dst_end, dst_end, 1);
   __ Addu(dst_end, dst_elements, dst_end);
+
+  // Allocating heap numbers in the loop below can fail and cause a jump to
+  // gc_required. We can't leave a partly initialized FixedArray behind,
+  // so pessimistically fill it with holes now.
+  Label initialization_loop, initialization_loop_entry;
+  __ LoadRoot(scratch, Heap::kTheHoleValueRootIndex);
+  __ Branch(&initialization_loop_entry);
+  __ bind(&initialization_loop);
+  __ sw(scratch, MemOperand(dst_elements));
+  __ Addu(dst_elements, dst_elements, Operand(kPointerSize));
+  __ bind(&initialization_loop_entry);
+  __ Branch(&initialization_loop, lt, dst_elements, Operand(dst_end));
+
+  __ Addu(dst_elements, array, Operand(FixedArray::kHeaderSize));
+  __ Addu(array, array, Operand(kHeapObjectTag));
   __ LoadRoot(heap_number_map, Heap::kHeapNumberMapRootIndex);
   // Using offsetted addresses.
   // dst_elements: begin of destination FixedArray element fields, not tagged
   // src_elements: begin of source FixedDoubleArray element fields, not tagged,
   //               points to the exponent
   // dst_end: end of destination FixedArray, not tagged
   // array: destination FixedArray
   // heap_number_map: heap number map
   __ Branch(&entry);
 
@@ skipping 331 matching lines @@
     patcher.masm()->nop();  // Pad the empty space.
   }
 }
 
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_MIPS