MIPS: port Fix GC-unsafe corner case in bit-not on ARM

src/mips/code-stubs-mips.cc

Index: src/mips/code-stubs-mips.cc
diff --git a/src/mips/code-stubs-mips.cc b/src/mips/code-stubs-mips.cc
index c9999949714127510e219802b767c3afae30b6d4..8867b19f0727a96f3f8aa9bd7f4921b0e256b49c 100644
--- a/src/mips/code-stubs-mips.cc
+++ b/src/mips/code-stubs-mips.cc
@@ -2002,6 +2002,8 @@ void UnaryOpStub::GenerateHeapNumberCodeSub(MacroAssembler* masm,
 void UnaryOpStub::GenerateHeapNumberCodeBitNot(
     MacroAssembler* masm,
     Label* slow) {
+  Label impossible;
+
   EmitCheckForHeapNumber(masm, a0, a1, t2, slow);
   // Convert the heap number in a0 to an untagged integer in a1.
   __ ConvertToInt32(a0, a1, a2, a3, f0, slow);
@@ -2020,17 +2022,28 @@ void UnaryOpStub::GenerateHeapNumberCodeBitNot(
   __ bind(&try_float);
   if (mode_ == UNARY_NO_OVERWRITE) {
     Label slow_allocate_heapnumber, heapnumber_allocated;
-    __ AllocateHeapNumber(v0, a2, a3, t2, &slow_allocate_heapnumber);
+    // Allocate a new heap number without zapping v0, which we need if it fails.
+    __ AllocateHeapNumber(a2, a3, t0, t2, &slow_allocate_heapnumber);
     __ jmp(&heapnumber_allocated);
 
     __ bind(&slow_allocate_heapnumber);
     __ EnterInternalFrame();
-    __ push(a1);
+    __ push(v0);  // Push the heap number, not the untagged int32.
     __ CallRuntime(Runtime::kNumberAlloc, 0);
-    __ pop(a1);
+    __ mov(a2, v0);  // Move the new heap number into a2.
+    // Get the heap number into v0, now that the new heap number is in a2.
+    __ pop(v0);
     __ LeaveInternalFrame();
 
+    // Convert the heap number in v0 to an untagged integer in a1.
+    // This can't go slow-case because it's the same number we already
+    // converted once again.
+    __ ConvertToInt32(v0, a1, a3, t0, f0, &impossible);
+    // Negate the result.
+    __ Xor(a1, a1, -1);
+
     __ bind(&heapnumber_allocated);
+    __ mov(v0, a2);  // Move newly allocated heap number to v0.
   }
 
   if (CpuFeatures::IsSupported(FPU)) {
@@ -2046,6 +2059,11 @@ void UnaryOpStub::GenerateHeapNumberCodeBitNot(
     WriteInt32ToHeapNumberStub stub(a1, v0, a2, a3);
     __ Jump(stub.GetCode(), RelocInfo::CODE_TARGET);
   }
+
+  __ bind(&impossible);
+  if (FLAG_debug_code) {
+    __ stop("Incorrect assumption in bit-not stub");
+  }
 }