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

Index: src/x64/code-stubs-x64.cc
diff --git a/src/x64/code-stubs-x64.cc b/src/x64/code-stubs-x64.cc
index 2ebfa1100b0abf0d7c733d16862ea5173656373f..20738817e90857d7a5565afd3189e265d24b4161 100644
--- a/src/x64/code-stubs-x64.cc
+++ b/src/x64/code-stubs-x64.cc
@@ -535,28 +535,33 @@ void TypeRecordingUnaryOpStub::GenerateHeapNumberCodeSub(MacroAssembler* masm,
                  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);
+  }
+
+  // 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);