Fix unary sub IC heap number code on x64: an untagged double was pushed on the stack and GCd.

src/x64/code-stubs-x64.cc

 // Copyright 2011 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 517 matching lines @@
 }
 
 
 void TypeRecordingUnaryOpStub::GenerateHeapNumberCodeSub(MacroAssembler* masm,
                                                          Label* slow) {
   // Check if the operand is a heap number.
   __ CompareRoot(FieldOperand(rax, HeapObject::kMapOffset),
                  Heap::kHeapNumberMapRootIndex);
   __ j(not_equal, slow);
 
-  // Operand is a float, negate its value by flipping sign bit.
-  __ movq(rdx, FieldOperand(rax, HeapNumber::kValueOffset));
-  __ Set(kScratchRegister, 0x01);
-  __ shl(kScratchRegister, Immediate(63));
-  __ xor_(rdx, kScratchRegister);  // Flip sign.
-  // rdx is value to store.
-  if (mode_ == UNARY_OVERWRITE) {
-    __ movq(FieldOperand(rax, HeapNumber::kValueOffset), rdx);
-  } else {
+  // Allocate a heap number (if necessary) before calculating the answer,
+  // so we don't have an untagged double around during GC.
+  if (mode_ != UNARY_OVERWRITE) {
     Label slow_allocate_heapnumber, heapnumber_allocated;
     __ AllocateHeapNumber(rcx, rbx, &slow_allocate_heapnumber);
     __ jmp(&heapnumber_allocated);
 
     __ bind(&slow_allocate_heapnumber);
     __ EnterInternalFrame();
-    __ push(rdx);
+    __ push(rax);
     __ CallRuntime(Runtime::kNumberAlloc, 0);
     __ movq(rcx, rax);
-    __ pop(rdx);
+    __ pop(rax);
     __ LeaveInternalFrame();
+    __ bind(&heapnumber_allocated);
+  }
 
-    __ bind(&heapnumber_allocated);
+  // Operand is a float, negate its value by flipping sign bit.
+  if (mode_ == UNARY_OVERWRITE) {

[Søren Thygesen Gjesse, 2011/05/02 12:46:25]

How about hoisting the loading of the scratch register?

+    __ Set(kScratchRegister, 0x01);
+    __ shl(kScratchRegister, Immediate(63));
+    __ xor_(FieldOperand(rax, HeapNumber::kValueOffset), kScratchRegister);
+  } else {
+    __ movq(rdx, FieldOperand(rax, HeapNumber::kValueOffset));
+    __ Set(kScratchRegister, 0x01);
+    __ shl(kScratchRegister, Immediate(63));
+    __ xor_(rdx, kScratchRegister);  // Flip sign.
     // rcx: allocated 'empty' number
     __ movq(FieldOperand(rcx, HeapNumber::kValueOffset), rdx);
     __ movq(rax, rcx);
   }
   __ ret(0);
 }
 
 
 void TypeRecordingUnaryOpStub::GenerateHeapNumberCodeBitNot(
     MacroAssembler* masm,
@@ skipping 4160 matching lines @@
   // Do a tail call to the rewritten stub.
   __ jmp(rdi);
 }
 
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64