diff --git a/js/src/devtools/rootAnalysis/loadCallgraph.js b/js/src/devtools/rootAnalysis/loadCallgraph.js
index 9ee8d76281..9723be5fc7 100644
--- a/js/src/devtools/rootAnalysis/loadCallgraph.js
+++ b/js/src/devtools/rootAnalysis/loadCallgraph.js
@@ -132,6 +132,12 @@ function loadCallgraph(file)
         addGCFunction(func, "annotation");
     }
 
+    // mess up the id <-> name correspondence. Also, we need to know if the
+    // functions even exist in the first place.)
+    for (var func of extraGCFunctions()) {
+        addGCFunction(func, "annotation");
+    }
+
     // Initialize suppressedFunctions to the set of all functions, and the
     // worklist to all toplevel callers.
     var worklist = [];
diff --git a/js/src/frontend/TokenStream.h b/js/src/frontend/TokenStream.h
index 6382c220ac..a1ab09f019 100644
--- a/js/src/frontend/TokenStream.h
+++ b/js/src/frontend/TokenStream.h
@@ -1020,7 +1020,7 @@ class MOZ_STACK_CLASS TokenStream
         return true;
     }
 
-    void skipChars(uint8_t n) {
+    void skipChars(uint32_t n) {
         while (n-- > 0) {
             MOZ_ASSERT(userbuf.hasRawChars());
             mozilla::DebugOnly<int32_t> c = getCharIgnoreEOL();
diff --git a/js/src/jit/BaselineCompiler.cpp b/js/src/jit/BaselineCompiler.cpp
index 282cdeaf9b..7673af7d5d 100644
--- a/js/src/jit/BaselineCompiler.cpp
+++ b/js/src/jit/BaselineCompiler.cpp
@@ -35,6 +35,7 @@
 #include "jit/MacroAssembler-inl.h"
 #include "vm/Interpreter-inl.h"
 #include "vm/NativeObject-inl.h"
+#include "vm/TypeInference-inl.h"
 
 using namespace js;
 using namespace js::jit;
@@ -97,7 +98,8 @@ BaselineCompiler::compile()
     AutoTraceLog logScript(logger, scriptEvent);
     AutoTraceLog logCompile(logger, TraceLogger_BaselineCompilation);
 
-    if (!script->ensureHasTypes(cx) || !script->ensureHasAnalyzedArgsUsage(cx))
+    AutoKeepTypeScripts keepTypes(cx);
+    if (!script->ensureHasTypes(cx, keepTypes) || !script->ensureHasAnalyzedArgsUsage(cx))
         return Method_Error;
 
     // When code coverage is only enabled for optimizations, or when a Debugger
diff --git a/js/src/jit/BaselineDebugModeOSR.cpp b/js/src/jit/BaselineDebugModeOSR.cpp
index aeb182c8e0..6614fb6709 100644
--- a/js/src/jit/BaselineDebugModeOSR.cpp
+++ b/js/src/jit/BaselineDebugModeOSR.cpp
@@ -16,6 +16,7 @@
 #include "jit/JitFrames-inl.h"
 #include "jit/MacroAssembler-inl.h"
 #include "vm/Stack-inl.h"
+#include "vm/TypeInference-inl.h"
 
 using namespace js;
 using namespace js::jit;
@@ -670,6 +671,7 @@ RecompileBaselineScriptForDebugMode(JSContext* cx, JSScript* script,
     JitSpew(JitSpew_BaselineDebugModeOSR, "Recompiling (%s:%" PRIuSIZE ") for %s",
             script->filename(), script->lineno(), observing ? "DEBUGGING" : "NORMAL EXECUTION");
 
+    AutoKeepTypeScripts keepTypes(cx);
     script->setBaselineScript(cx->runtime(), nullptr);
 
     MethodStatus status = BaselineCompile(cx, script, /* forceDebugMode = */ observing);
diff --git a/js/src/jit/IonAnalysis.cpp b/js/src/jit/IonAnalysis.cpp
index 0e511e07d0..004cf10775 100644
--- a/js/src/jit/IonAnalysis.cpp
+++ b/js/src/jit/IonAnalysis.cpp
@@ -4180,7 +4180,8 @@ jit::AnalyzeArgumentsUsage(JSContext* cx, JSScript* scriptArg)
     if (script->length() > MAX_SCRIPT_SIZE)
         return true;
 
-    if (!script->ensureHasTypes(cx))
+    AutoKeepTypeScripts keepTypes(cx);
+    if (!script->ensureHasTypes(cx, keepTypes))
         return false;
 
     TraceLoggerThread* logger = TraceLoggerForMainThread(cx->runtime());
diff --git a/js/src/jit/IonCacheIRCompiler.cpp b/js/src/jit/IonCacheIRCompiler.cpp
index 15cf7c6b0f..9a5ced2dbd 100644
--- a/js/src/jit/IonCacheIRCompiler.cpp
+++ b/js/src/jit/IonCacheIRCompiler.cpp
@@ -1226,9 +1226,9 @@ IonCacheIRCompiler::emitCallStringSplitResult()
 static bool
 GroupHasPropertyTypes(ObjectGroup* group, jsid* id, Value* v)
 {
-    if (group->unknownProperties())
+    if (group->unknownPropertiesDontCheckGeneration())
         return true;
-    HeapTypeSet* propTypes = group->maybeGetProperty(*id);
+    HeapTypeSet* propTypes = group->maybeGetPropertyDontCheckGeneration(*id);
     if (!propTypes)
         return true;
     if (!propTypes->nonConstantProperty())
diff --git a/js/src/jit/VMFunctions.cpp b/js/src/jit/VMFunctions.cpp
index 68e4eb30e4..812c9792a1 100644
--- a/js/src/jit/VMFunctions.cpp
+++ b/js/src/jit/VMFunctions.cpp
@@ -544,7 +544,8 @@ CreateThis(JSContext* cx, HandleObject callee, HandleObject newTarget, MutableHa
         RootedFunction fun(cx, &callee->as<JSFunction>());
         if (fun->isInterpreted() && fun->isConstructor()) {
             JSScript* script = JSFunction::getOrCreateScript(cx, fun);
-            if (!script || !script->ensureHasTypes(cx))
+            AutoKeepTypeScripts keepTypes(cx);
+            if (!script || !script->ensureHasTypes(cx, keepTypes))
                 return false;
             if (fun->isBoundFunction() || script->isDerivedClassConstructor()) {
                 rval.set(MagicValue(JS_UNINITIALIZED_LEXICAL));
diff --git a/js/src/jit/arm/Assembler-arm.cpp b/js/src/jit/arm/Assembler-arm.cpp
index c7e9d86576..a61634bc2f 100644
--- a/js/src/jit/arm/Assembler-arm.cpp
+++ b/js/src/jit/arm/Assembler-arm.cpp
@@ -863,7 +863,7 @@ template <class Iter>
 static void
 TraceOneDataRelocation(JSTracer* trc, Iter* iter)
 {
-    Instruction* ins = iter->cur();
+    Iter iterCopy(*iter);
     Register dest;
     Assembler::RelocStyle rs;
     const void* prior = Assembler::GetPtr32Target(iter, &dest, &rs);
@@ -874,12 +874,12 @@ TraceOneDataRelocation(JSTracer* trc, Iter* iter)
                                              "ion-masm-ptr");
 
     if (ptr != prior) {
-        MacroAssemblerARM::ma_mov_patch(Imm32(int32_t(ptr)), dest, Assembler::Always, rs, ins);
+        MacroAssemblerARM::ma_mov_patch(Imm32(int32_t(ptr)), dest, Assembler::Always, rs, iterCopy);
 
         // L_LDR won't cause any instructions to be updated.
         if (rs != Assembler::L_LDR) {
-            AutoFlushICache::flush(uintptr_t(ins), 4);
-            AutoFlushICache::flush(uintptr_t(ins->next()), 4);
+            AutoFlushICache::flush(uintptr_t(iter->cur()), 4);
+            AutoFlushICache::flush(uintptr_t(iter->next()), 4);
         }
     }
 }
@@ -899,7 +899,7 @@ TraceDataRelocations(JSTracer* trc, ARMBuffer* buffer, CompactBufferReader& read
 {
     while (reader.more()) {
         BufferOffset offset(reader.readUnsigned());
-        ARMBuffer::AssemblerBufferInstIterator iter(offset, buffer);
+        BufferInstructionIterator iter(offset, buffer);
         TraceOneDataRelocation(trc, &iter);
     }
 }
@@ -3161,14 +3161,15 @@ Assembler::PatchDataWithValueCheck(CodeLocationLabel label, PatchedImmPtr newVal
                                    PatchedImmPtr expectedValue)
 {
     Instruction* ptr = reinterpret_cast<Instruction*>(label.raw());
-    InstructionIterator iter(ptr);
     Register dest;
     Assembler::RelocStyle rs;
 
+    InstructionIterator iter(ptr);
     DebugOnly<const uint32_t*> val = GetPtr32Target(&iter, &dest, &rs);
     MOZ_ASSERT(uint32_t((const uint32_t*)val) == uint32_t(expectedValue.value));
 
-    MacroAssembler::ma_mov_patch(Imm32(int32_t(newValue.value)), dest, Always, rs, ptr);
+    iter = InstructionIterator(ptr);
+    MacroAssembler::ma_mov_patch(Imm32(int32_t(newValue.value)), dest, Always, rs, iter);
 
     // L_LDR won't cause any instructions to be updated.
     if (rs != L_LDR) {
@@ -3221,6 +3222,20 @@ InstIsGuard(Instruction* inst, const PoolHeader** ph)
     return *ph != nullptr;
 }
 
+static bool
+InstIsGuard(BufferInstructionIterator& iter, const PoolHeader** ph)
+{
+    Instruction* inst = iter.cur();
+    Assembler::Condition c = inst->extractCond();
+    if (c != Assembler::Always)
+        return false;
+    if (!(inst->is<InstBXReg>() || inst->is<InstBImm>()))
+        return false;
+    // See if the next instruction is a pool header.
+    *ph = iter.peek()->as<const PoolHeader>();
+    return *ph != nullptr;
+}
+
 static bool
 InstIsBNop(Instruction* inst)
 {
@@ -3266,6 +3281,28 @@ Instruction::skipPool()
     return this;
 }
 
+void
+BufferInstructionIterator::skipPool()
+{
+    // If this is a guard, and the next instruction is a header, always work
+    // around the pool. If it isn't a guard, then start looking ahead.
+
+    const PoolHeader* ph;
+    if (InstIsGuard(*this, &ph)) {
+        // Don't skip a natural guard.
+        if (ph->isNatural())
+            return;
+        advance(sizeof(Instruction) * (1 + ph->size()));
+        skipPool();
+        return;
+    }
+
+    if (InstIsBNop(cur())) {
+        next();
+        skipPool();
+    }
+}
+
 // Cases to be handled:
 // 1) no pools or branches in sight => return this+1
 // 2) branch to next instruction => return this+2, because a nop needed to be inserted into the stream.
@@ -3409,13 +3446,6 @@ Assembler::BailoutTableStart(uint8_t* code)
     return (uint8_t*) inst;
 }
 
-InstructionIterator::InstructionIterator(Instruction* i_)
-  : i(i_)
-{
-    // Work around pools with an artificial pool guard and around nop-fill.
-    i = i->skipPool();
-}
-
 uint32_t Assembler::NopFill = 0;
 
 uint32_t
diff --git a/js/src/jit/arm/Assembler-arm.h b/js/src/jit/arm/Assembler-arm.h
index 98d26131c9..04e5e1f129 100644
--- a/js/src/jit/arm/Assembler-arm.h
+++ b/js/src/jit/arm/Assembler-arm.h
@@ -2246,20 +2246,35 @@ class InstMOV : public InstALU
 class InstructionIterator
 {
   private:
-    Instruction* i;
+    Instruction* inst_;
 
   public:
-    explicit InstructionIterator(Instruction* i_);
+    explicit InstructionIterator(Instruction* inst) : inst_(inst) {
+        skipPool();
+    }
+    void skipPool() {
+        inst_ = inst_->skipPool();
+    }
 
     Instruction* next() {
-        i = i->next();
+        inst_ = inst_->next();
         return cur();
     }
     Instruction* cur() const {
-        return i;
+        return inst_;
     }
 };
 
+class BufferInstructionIterator : public ARMBuffer::AssemblerBufferInstIterator
+{
+  public:
+    BufferInstructionIterator(BufferOffset bo, ARMBuffer* buffer)
+      : ARMBuffer::AssemblerBufferInstIterator(bo, buffer)
+    {}
+    void skipPool();
+};
+
+
 static const uint32_t NumIntArgRegs = 4;
 
 // There are 16 *float* registers available for arguments
diff --git a/js/src/jit/arm/MacroAssembler-arm-inl.h b/js/src/jit/arm/MacroAssembler-arm-inl.h
index 3fc07e0de5..33fcb01392 100644
--- a/js/src/jit/arm/MacroAssembler-arm-inl.h
+++ b/js/src/jit/arm/MacroAssembler-arm-inl.h
@@ -308,6 +308,25 @@ MacroAssembler::add64(Imm64 imm, Register64 dest)
     ma_adc(imm.hi(), dest.high, scratch, LeaveCC);
 }
 
+CodeOffset
+MacroAssembler::add32ToPtrWithPatch(Register src, Register dest)
+{
+    ScratchRegisterScope scratch(*this);
+    CodeOffset offs = CodeOffset(currentOffset());
+    ma_movPatchable(Imm32(0), scratch, Always);
+    ma_add(src, scratch, dest);
+    return offs;
+}
+
+void
+MacroAssembler::patchAdd32ToPtr(CodeOffset offset, Imm32 imm)
+{
+    ScratchRegisterScope scratch(*this);
+    BufferInstructionIterator iter(BufferOffset(offset.offset()), &m_buffer);
+    iter.maybeSkipAutomaticInstructions();
+    ma_mov_patch(imm, scratch, Always, HasMOVWT() ? L_MOVWT : L_LDR, iter);
+}
+
 void
 MacroAssembler::addDouble(FloatRegister src, FloatRegister dest)
 {
diff --git a/js/src/jit/arm/MacroAssembler-arm.cpp b/js/src/jit/arm/MacroAssembler-arm.cpp
index 7b91f6527f..3741b273c6 100644
--- a/js/src/jit/arm/MacroAssembler-arm.cpp
+++ b/js/src/jit/arm/MacroAssembler-arm.cpp
@@ -345,35 +345,36 @@ MacroAssemblerARM::ma_movPatchable(ImmPtr imm, Register dest, Assembler::Conditi
     ma_movPatchable(Imm32(int32_t(imm.value)), dest, c);
 }
 
-/* static */ void
-MacroAssemblerARM::ma_mov_patch(Imm32 imm_, Register dest, Assembler::Condition c,
-                                RelocStyle rs, Instruction* i)
+/* static */
+template<class Iter>
+void
+MacroAssemblerARM::ma_mov_patch(Imm32 imm32, Register dest, Assembler::Condition c,
+                                RelocStyle rs, Iter iter)
 {
-    MOZ_ASSERT(i);
-    int32_t imm = imm_.value;
+    MOZ_ASSERT(iter.cur());
 
     // Make sure the current instruction is not an artificial guard inserted
     // by the assembler buffer.
-    i = i->skipPool();
+    iter.skipPool();
+
+    int32_t imm = imm32.value;
 
     switch(rs) {
       case L_MOVWT:
-        Assembler::as_movw_patch(dest, Imm16(imm & 0xffff), c, i);
-        i = i->next();
-        Assembler::as_movt_patch(dest, Imm16(imm >> 16 & 0xffff), c, i);
+        Assembler::as_movw_patch(dest, Imm16(imm & 0xffff), c, iter.cur());
+        Assembler::as_movt_patch(dest, Imm16(imm >> 16 & 0xffff), c, iter.next());
         break;
       case L_LDR:
-        Assembler::WritePoolEntry(i, c, imm);
+        Assembler::WritePoolEntry(iter.cur(), c, imm);
         break;
     }
 }
-
-/* static */ void
-MacroAssemblerARM::ma_mov_patch(ImmPtr imm, Register dest, Assembler::Condition c,
-                                RelocStyle rs, Instruction* i)
-{
-    ma_mov_patch(Imm32(int32_t(imm.value)), dest, c, rs, i);
-}
+template void
+MacroAssemblerARM::ma_mov_patch(Imm32 imm32, Register dest, Assembler::Condition c,
+                                RelocStyle rs, InstructionIterator iter);
+template void
+MacroAssemblerARM::ma_mov_patch(Imm32 imm32, Register dest, Assembler::Condition c,
+                                RelocStyle rs, BufferInstructionIterator iter);
 
 void
 MacroAssemblerARM::ma_mov(Register src, Register dest, SBit s, Assembler::Condition c)
diff --git a/js/src/jit/arm/MacroAssembler-arm.h b/js/src/jit/arm/MacroAssembler-arm.h
index 218939c2a4..99640e445b 100644
--- a/js/src/jit/arm/MacroAssembler-arm.h
+++ b/js/src/jit/arm/MacroAssembler-arm.h
@@ -124,10 +124,10 @@ class MacroAssemblerARM : public Assembler
     void ma_movPatchable(Imm32 imm, Register dest, Assembler::Condition c);
     void ma_movPatchable(ImmPtr imm, Register dest, Assembler::Condition c);
 
+    // To be used with Iter := InstructionIterator or BufferInstructionIterator.
+    template<class Iter>
     static void ma_mov_patch(Imm32 imm, Register dest, Assembler::Condition c,
-                             RelocStyle rs, Instruction* i);
-    static void ma_mov_patch(ImmPtr imm, Register dest, Assembler::Condition c,
-                             RelocStyle rs, Instruction* i);
+                             RelocStyle rs, Iter iter);
 
     // ALU based ops
     // mov
diff --git a/js/src/jit/shared/IonAssemblerBuffer.h b/js/src/jit/shared/IonAssemblerBuffer.h
index b6af126bc8..4365561fbf 100644
--- a/js/src/jit/shared/IonAssemblerBuffer.h
+++ b/js/src/jit/shared/IonAssemblerBuffer.h
@@ -141,7 +141,6 @@ class AssemblerBuffer
 {
   protected:
     typedef BufferSlice<SliceSize> Slice;
-    typedef AssemblerBuffer<SliceSize, Inst> AssemblerBuffer_;
 
     // Doubly-linked list of BufferSlices, with the most recent in tail position.
     Slice* head;
@@ -388,24 +387,32 @@ class AssemblerBuffer
         return BufferOffset(bufferSize);
     }
 
+    typedef AssemblerBuffer<SliceSize, Inst> ThisClass;
+
     class AssemblerBufferInstIterator
     {
-        BufferOffset bo;
-        AssemblerBuffer_* m_buffer;
+        BufferOffset bo_;
+        ThisClass* buffer_;
 
       public:
-        explicit AssemblerBufferInstIterator(BufferOffset off, AssemblerBuffer_* buffer)
-          : bo(off), m_buffer(buffer)
+        explicit AssemblerBufferInstIterator(BufferOffset bo, ThisClass* buffer)
+          : bo_(bo), buffer_(buffer)
         { }
 
+        void advance(int offset) {
+            bo_ = BufferOffset(bo_.getOffset() + offset);
+        }
+
         Inst* next() {
-            Inst* i = m_buffer->getInst(bo);
-            bo = BufferOffset(bo.getOffset() + i->size());
+            advance(cur()->size());
             return cur();
         }
 
-        Inst* cur() {
-            return m_buffer->getInst(bo);
+        Inst* peek() {
+            return buffer_->getInst(BufferOffset(bo_.getOffset() + cur()->size()));
+        }
+        Inst* cur() const {
+            return buffer_->getInst(bo_);
         }
     };
 };
diff --git a/js/src/jsscript.h b/js/src/jsscript.h
index 9cfebe68cb..2d761d0e88 100644
--- a/js/src/jsscript.h
+++ b/js/src/jsscript.h
@@ -1689,7 +1689,7 @@ class JSScript : public js::gc::TenuredCell
     bool isTopLevel() { return code() && !functionNonDelazifying(); }
 
     /* Ensure the script has a TypeScript. */
-    inline bool ensureHasTypes(JSContext* cx);
+    inline bool ensureHasTypes(JSContext* cx, js::AutoKeepTypeScripts&);
 
     inline js::TypeScript* types();
 
diff --git a/js/src/vm/EnvironmentObject.cpp b/js/src/vm/EnvironmentObject.cpp
index 5ea7971e0e..0ec095b70a 100644
--- a/js/src/vm/EnvironmentObject.cpp
+++ b/js/src/vm/EnvironmentObject.cpp
@@ -28,6 +28,7 @@
 #include "jsscriptinlines.h"
 
 #include "vm/Stack-inl.h"
+#include "vm/TypeInference-inl.h"
 
 using namespace js;
 using namespace js::gc;
@@ -1466,7 +1467,8 @@ class DebugEnvironmentProxyHandler : public BaseProxyHandler
             CallObject& callobj = env->as<CallObject>();
             RootedFunction fun(cx, &callobj.callee());
             RootedScript script(cx, JSFunction::getOrCreateScript(cx, fun));
-            if (!script->ensureHasTypes(cx) || !script->ensureHasAnalyzedArgsUsage(cx))
+            AutoKeepTypeScripts keepTypes(cx);
+            if (!script->ensureHasTypes(cx, keepTypes) || !script->ensureHasAnalyzedArgsUsage(cx))
                 return false;
 
             BindingIter bi(script);
diff --git a/js/src/vm/ObjectGroup.h b/js/src/vm/ObjectGroup.h
index 298178f020..fd273af0f4 100644
--- a/js/src/vm/ObjectGroup.h
+++ b/js/src/vm/ObjectGroup.h
@@ -383,7 +383,8 @@ class ObjectGroup : public gc::TenuredCell
     inline HeapTypeSet* getProperty(ExclusiveContext* cx, JSObject* obj, jsid id);
 
     /* Get a property only if it already exists. */
-    inline HeapTypeSet* maybeGetProperty(jsid id);
+    MOZ_ALWAYS_INLINE HeapTypeSet* maybeGetProperty(jsid id);
+    MOZ_ALWAYS_INLINE HeapTypeSet* maybeGetPropertyDontCheckGeneration(jsid id);
 
     /*
      * Iterate through the group's properties. getPropertyCount overapproximates
@@ -461,6 +462,7 @@ class ObjectGroup : public gc::TenuredCell
     }
 
     inline uint32_t basePropertyCount();
+    inline uint32_t basePropertyCountDontCheckGeneration();
 
   private:
     inline void setBasePropertyCount(uint32_t count);
diff --git a/js/src/vm/TypeInference-inl.h b/js/src/vm/TypeInference-inl.h
index 8c9b179223..ba5004a282 100644
--- a/js/src/vm/TypeInference-inl.h
+++ b/js/src/vm/TypeInference-inl.h
@@ -367,10 +367,10 @@ TypeMonitorCall(JSContext* cx, const js::CallArgs& args, bool constructing)
 inline bool
 TrackPropertyTypes(ExclusiveContext* cx, JSObject* obj, jsid id)
 {
-    if (obj->hasLazyGroup() || obj->group()->unknownProperties())
+    if (obj->hasLazyGroup() || obj->group()->unknownPropertiesDontCheckGeneration())
         return false;
 
-    if (obj->isSingleton() && !obj->group()->maybeGetProperty(id))
+    if (obj->isSingleton() && !obj->group()->maybeGetPropertyDontCheckGeneration(id))
         return false;
 
     return true;
@@ -405,7 +405,15 @@ PropertyHasBeenMarkedNonConstant(JSObject* obj, jsid id)
 inline bool
 HasTypePropertyId(JSObject* obj, jsid id, TypeSet::Type type)
 {
-    if (obj->hasLazyGroup())
+    MOZ_ASSERT(id == IdToTypeId(id));
+    MOZ_ASSERT(TrackPropertyTypes(obj, id));
+
+    if (HeapTypeSet* types = obj->group()->maybeGetPropertyDontCheckGeneration(id)) {
+        if (!types->hasType(type))
+            return false;
+        // Non-constant properties are only relevant for singleton objects.
+        if (obj->isSingleton() && !types->nonConstantProperty())
+            return false;
         return true;
 
     if (obj->group()->unknownProperties())
@@ -657,6 +665,21 @@ TypeScript::SetArgument(JSContext* cx, JSScript* script, unsigned arg, const js:
     SetArgument(cx, script, arg, TypeSet::GetValueType(value));
 }
 
+inline
+AutoKeepTypeScripts::AutoKeepTypeScripts(JSContext* cx)
+  : zone_(cx->zone()->types),
+    prev_(zone_.keepTypeScripts)
+{
+    zone_.keepTypeScripts = true;
+}
+
+inline
+AutoKeepTypeScripts::~AutoKeepTypeScripts()
+{
+    MOZ_ASSERT(zone_.keepTypeScripts);
+    zone_.keepTypeScripts = prev_;
+}
+
 /////////////////////////////////////////////////////////////////////
 // TypeHashSet
 /////////////////////////////////////////////////////////////////////
@@ -1024,10 +1047,18 @@ TypeSet::getObjectClass(unsigned i) const
 // ObjectGroup
 /////////////////////////////////////////////////////////////////////
 
+inline uint32_t
+ObjectGroup::basePropertyCountDontCheckGeneration()
+{
+    uint32_t flags = flagsDontCheckGeneration();
+    return (flags & OBJECT_FLAG_PROPERTY_COUNT_MASK) >> OBJECT_FLAG_PROPERTY_COUNT_SHIFT;
+}
+
 inline uint32_t
 ObjectGroup::basePropertyCount()
 {
-    return (flags() & OBJECT_FLAG_PROPERTY_COUNT_MASK) >> OBJECT_FLAG_PROPERTY_COUNT_SHIFT;
+    maybeSweep(nullptr);
+    return basePropertyCountDontCheckGeneration();
 }
 
 inline void
@@ -1083,18 +1114,25 @@ ObjectGroup::getProperty(ExclusiveContext* cx, JSObject* obj, jsid id)
 }
 
 inline HeapTypeSet*
-ObjectGroup::maybeGetProperty(jsid id)
+ObjectGroup::maybeGetPropertyDontCheckGeneration(jsid id)
 {
     MOZ_ASSERT(JSID_IS_VOID(id) || JSID_IS_EMPTY(id) || JSID_IS_STRING(id) || JSID_IS_SYMBOL(id));
     MOZ_ASSERT_IF(!JSID_IS_EMPTY(id), id == IdToTypeId(id));
-    MOZ_ASSERT(!unknownProperties());
+    MOZ_ASSERT(!unknownPropertiesDontCheckGeneration());
 
     Property* prop = TypeHashSet::Lookup<jsid, Property, Property>
-                         (propertySet, basePropertyCount(), id);
+                         (propertySet, basePropertyCountDontCheckGeneration(), id);
 
     return prop ? &prop->types : nullptr;
 }
 
+inline HeapTypeSet*
+ObjectGroup::maybeGetProperty(jsid id)
+{
+    maybeSweep(nullptr);
+    return maybeGetPropertyDontCheckGeneration(id);
+}
+
 inline unsigned
 ObjectGroup::getPropertyCount()
 {
@@ -1125,7 +1163,7 @@ JSScript::types()
 }
 
 inline bool
-JSScript::ensureHasTypes(JSContext* cx)
+JSScript::ensureHasTypes(JSContext* cx, js::AutoKeepTypeScripts&)
 {
     return types() || makeTypes(cx);
 }
diff --git a/js/src/vm/TypeInference.cpp b/js/src/vm/TypeInference.cpp
index 31fd9af6e3..d086b556e8 100644
--- a/js/src/vm/TypeInference.cpp
+++ b/js/src/vm/TypeInference.cpp
@@ -4436,6 +4436,7 @@ JSScript::maybeSweepTypes(AutoClearTypeInferenceStateOnOOM* oom)
     // only do this if nothing has been compiled for the script, which will be
     // the case unless the script has been compiled since we started sweeping.
     if (types.sweepReleaseTypes &&
+        !types.keepTypeScripts &&
         !hasBaselineScript() &&
         !hasIonScript())
     {
@@ -4492,20 +4493,24 @@ Zone::addSizeOfIncludingThis(mozilla::MallocSizeOf mallocSizeOf,
 
 TypeZone::TypeZone(Zone* zone)
   : zone_(zone),
-    typeLifoAlloc(TYPE_LIFO_ALLOC_PRIMARY_CHUNK_SIZE),
-    generation(0),
-    compilerOutputs(nullptr),
-    sweepTypeLifoAlloc(TYPE_LIFO_ALLOC_PRIMARY_CHUNK_SIZE),
-    sweepCompilerOutputs(nullptr),
-    sweepReleaseTypes(false),
-    activeAnalysis(nullptr)
+    typeLifoAlloc(zone->group(), (size_t) TYPE_LIFO_ALLOC_PRIMARY_CHUNK_SIZE),
+    generation(zone->group(), 0),
+    compilerOutputs(zone->group(), nullptr),
+    sweepTypeLifoAlloc(zone->group(), (size_t) TYPE_LIFO_ALLOC_PRIMARY_CHUNK_SIZE),
+    sweepCompilerOutputs(zone->group(), nullptr),
+    sweepReleaseTypes(zone->group(), false),
+    sweepingTypes(zone->group(), false),
+    keepTypeScripts(zone->group(), false),
+    activeAnalysis(zone->group(), nullptr)
 {
 }
 
 TypeZone::~TypeZone()
 {
-    js_delete(compilerOutputs);
-    js_delete(sweepCompilerOutputs);
+    js_delete(compilerOutputs.ref());
+    js_delete(sweepCompilerOutputs.ref());
+    MOZ_RELEASE_ASSERT(!sweepingTypes);
+    MOZ_ASSERT(!keepTypeScripts);
 }
 
 void
diff --git a/js/src/vm/TypeInference.h b/js/src/vm/TypeInference.h
index ae593a4e73..4f823b95b8 100644
--- a/js/src/vm/TypeInference.h
+++ b/js/src/vm/TypeInference.h
@@ -1255,6 +1255,19 @@ class TypeScript
 #endif
 };
 
+// Ensures no TypeScripts are purged in the current zone.
+class MOZ_RAII AutoKeepTypeScripts
+{
+    TypeZone& zone_;
+    bool prev_;
+
+    AutoKeepTypeScripts(const AutoKeepTypeScripts&) = delete;
+    void operator=(const AutoKeepTypeScripts&) = delete;
+
+  public:
+    explicit inline AutoKeepTypeScripts(JSContext* cx);
+    inline ~AutoKeepTypeScripts();
+};
 void
 FillBytecodeTypeMap(JSScript* script, uint32_t* bytecodeMap);
 
@@ -1325,6 +1338,9 @@ struct TypeZone
     static const size_t TYPE_LIFO_ALLOC_PRIMARY_CHUNK_SIZE = 8 * 1024;
     LifoAlloc typeLifoAlloc;
 
+    TypeZone(const TypeZone&) = delete;
+    void operator=(const TypeZone&) = delete;
+
     // Current generation for sweeping.
     uint32_t generation : 1;
 
@@ -1348,6 +1364,7 @@ struct TypeZone
     // information attached to scripts.
     bool sweepReleaseTypes;
 
+    ZoneGroupData<bool> keepTypeScripts;
     // The topmost AutoEnterAnalysis on the stack, if there is one.
     AutoEnterAnalysis* activeAnalysis;
 
diff --git a/js/src/vm/UnboxedObject.cpp b/js/src/vm/UnboxedObject.cpp
index 2ed89e32e4..07e78d8a6d 100644
--- a/js/src/vm/UnboxedObject.cpp
+++ b/js/src/vm/UnboxedObject.cpp
@@ -362,7 +362,7 @@ UnboxedPlainObject::ensureExpando(JSContext* cx, Handle<UnboxedPlainObject*> obj
 bool
 UnboxedPlainObject::containsUnboxedOrExpandoProperty(ExclusiveContext* cx, jsid id) const
 {
-    if (layout().lookup(id))
+    if (layoutDontCheckGeneration().lookup(id))
         return true;
 
     if (maybeExpando() && maybeExpando()->containsShapeOrElement(cx, id))