Vector-ICs - speed towards the monomorphic exit as quickly as possible.

Thanks to some careful assumptions, we can examine the object found at
vector[slot] and trust it's a heap object where the second field is
either a map if it's a WeakCell, or definitely not a map if it's a
Symbol, String or FixedArray. Use this to save a memory read.

BUG=

Review URL: https://codereview.chromium.org/1032163002

Cr-Commit-Position: refs/heads/master@{#27631}

src/arm/assembler-arm.h

@@ -162,9 +162,9 @@ const Register r3  = { kRegister_r3_Code };
 const Register r4  = { kRegister_r4_Code };
 const Register r5  = { kRegister_r5_Code };
 const Register r6  = { kRegister_r6_Code };
-// Used as constant pool pointer register if FLAG_enable_ool_constant_pool.
-const Register r7  = { kRegister_r7_Code };
 // Used as context register.
+const Register r7 = {kRegister_r7_Code};
+// Used as constant pool pointer register if FLAG_enable_ool_constant_pool.
 const Register r8  = { kRegister_r8_Code };
 // Used as lithium codegen scratch register.
 const Register r9  = { kRegister_r9_Code };

src/arm/code-stubs-arm.cc

@@ -4369,21 +4369,15 @@ void VectorRawLoadStub::GenerateForTrampoline(MacroAssembler* masm) {
 
 static void HandleArrayCases(MacroAssembler* masm, Register receiver,
                              Register key, Register vector, Register slot,
-                             Register feedback, Register scratch1,
-                             Register scratch2, Register scratch3,
+                             Register feedback, Register receiver_map,
+                             Register scratch1, Register scratch2,
                              bool is_polymorphic, Label* miss) {
   // feedback initially contains the feedback array
   Label next_loop, prepare_next;
-  Label load_smi_map, compare_map;
   Label start_polymorphic;
 
-  Register receiver_map = scratch1;
-  Register cached_map = scratch2;
+  Register cached_map = scratch1;
 
-  // Receiver might not be a heap object.
-  __ JumpIfSmi(receiver, &load_smi_map);
-  __ ldr(receiver_map, FieldMemOperand(receiver, HeapObject::kMapOffset));
-  __ bind(&compare_map);
   __ ldr(cached_map,
          FieldMemOperand(feedback, FixedArray::OffsetOfElementAt(0)));
   __ ldr(cached_map, FieldMemOperand(cached_map, WeakCell::kValueOffset));
@@ -4395,7 +4389,7 @@ static void HandleArrayCases(MacroAssembler* masm, Register receiver,
   __ add(pc, handler, Operand(Code::kHeaderSize - kHeapObjectTag));
 
 
-  Register length = scratch3;
+  Register length = scratch2;
   __ bind(&start_polymorphic);
   __ ldr(length, FieldMemOperand(feedback, FixedArray::kLengthOffset));
   if (!is_polymorphic) {
@@ -4415,9 +4409,9 @@ static void HandleArrayCases(MacroAssembler* masm, Register receiver,
   //                              ^              ^
   //                              |              |
   //                         pointer_reg      too_far
-  //                         aka feedback     scratch3
-  // also need receiver_map (aka scratch1)
-  // use cached_map (scratch2) to look in the weak map values.
+  //                         aka feedback     scratch2
+  // also need receiver_map
+  // use cached_map (scratch1) to look in the weak map values.
   __ add(too_far, feedback, Operand::PointerOffsetFromSmiKey(length));
   __ add(too_far, too_far, Operand(FixedArray::kHeaderSize - kHeapObjectTag));
   __ add(pointer_reg, feedback,
@@ -4438,42 +4432,23 @@ static void HandleArrayCases(MacroAssembler* masm, Register receiver,
 
   // We exhausted our array of map handler pairs.
   __ jmp(miss);
-
-  __ bind(&load_smi_map);
-  __ LoadRoot(receiver_map, Heap::kHeapNumberMapRootIndex);
-  __ jmp(&compare_map);
 }
 
 
 static void HandleMonomorphicCase(MacroAssembler* masm, Register receiver,
-                                  Register key, Register vector, Register slot,
-                                  Register weak_cell, Register scratch,
-                                  Label* miss) {
-  // feedback initially contains the feedback array
-  Label compare_smi_map;
-  Register receiver_map = scratch;
-  Register cached_map = weak_cell;
-
-  // Move the weak map into the weak_cell register.
-  __ ldr(cached_map, FieldMemOperand(weak_cell, WeakCell::kValueOffset));
-
-  // Receiver might not be a heap object.
-  __ JumpIfSmi(receiver, &compare_smi_map);
+                                  Register receiver_map, Register feedback,
+                                  Register vector, Register slot,
+                                  Register scratch, Label* compare_map,
+                                  Label* load_smi_map, Label* try_array) {
+  __ JumpIfSmi(receiver, load_smi_map);
   __ ldr(receiver_map, FieldMemOperand(receiver, HeapObject::kMapOffset));
+  __ bind(compare_map);
+  Register cached_map = scratch;
+  // Move the weak map into the weak_cell register.
+  __ ldr(cached_map, FieldMemOperand(feedback, WeakCell::kValueOffset));
   __ cmp(cached_map, receiver_map);
-  __ b(ne, miss);
-
-  Register handler = weak_cell;
-  __ add(handler, vector, Operand::PointerOffsetFromSmiKey(slot));
-  __ ldr(handler,
-         FieldMemOperand(handler, FixedArray::kHeaderSize + kPointerSize));
-  __ add(pc, handler, Operand(Code::kHeaderSize - kHeapObjectTag));
-
-  // In microbenchmarks, it made sense to unroll this code so that the call to
-  // the handler is duplicated for a HeapObject receiver and a Smi receiver.
-  __ bind(&compare_smi_map);
-  __ CompareRoot(weak_cell, Heap::kHeapNumberMapRootIndex);
-  __ b(ne, miss);
+  __ b(ne, try_array);
+  Register handler = feedback;
   __ add(handler, vector, Operand::PointerOffsetFromSmiKey(slot));
   __ ldr(handler,
          FieldMemOperand(handler, FixedArray::kHeaderSize + kPointerSize));
@@ -4487,26 +4462,27 @@ void VectorRawLoadStub::GenerateImpl(MacroAssembler* masm, bool in_frame) {
   Register vector = VectorLoadICDescriptor::VectorRegister();      // r3
   Register slot = VectorLoadICDescriptor::SlotRegister();          // r0
   Register feedback = r4;
-  Register scratch1 = r5;
+  Register receiver_map = r5;
+  Register scratch1 = r8;
 
   __ add(feedback, vector, Operand::PointerOffsetFromSmiKey(slot));
   __ ldr(feedback, FieldMemOperand(feedback, FixedArray::kHeaderSize));
 
-  // Is it a weak cell?
-  Label try_array;
-  Label not_array, smi_key, key_okay, miss;
-  __ ldr(scratch1, FieldMemOperand(feedback, HeapObject::kMapOffset));
-  __ CompareRoot(scratch1, Heap::kWeakCellMapRootIndex);
-  __ b(ne, &try_array);
-  HandleMonomorphicCase(masm, receiver, name, vector, slot, feedback, scratch1,
-                        &miss);
+  // Try to quickly handle the monomorphic case without knowing for sure
+  // if we have a weak cell in feedback. We do know it's safe to look
+  // at WeakCell::kValueOffset.
+  Label try_array, load_smi_map, compare_map;
+  Label not_array, miss;
+  HandleMonomorphicCase(masm, receiver, receiver_map, feedback, vector, slot,
+                        scratch1, &compare_map, &load_smi_map, &try_array);
 
   // Is it a fixed array?
   __ bind(&try_array);
+  __ ldr(scratch1, FieldMemOperand(feedback, HeapObject::kMapOffset));
   __ CompareRoot(scratch1, Heap::kFixedArrayMapRootIndex);
   __ b(ne, &not_array);
-  HandleArrayCases(masm, receiver, name, vector, slot, feedback, scratch1, r8,
-                   r9, true, &miss);
+  HandleArrayCases(masm, receiver, name, vector, slot, feedback, receiver_map,
+                   scratch1, r9, true, &miss);
 
   __ bind(&not_array);
   __ CompareRoot(feedback, Heap::kmegamorphic_symbolRootIndex);
@@ -4515,10 +4491,15 @@ void VectorRawLoadStub::GenerateImpl(MacroAssembler* masm, bool in_frame) {
       Code::ComputeHandlerFlags(Code::LOAD_IC));
   masm->isolate()->stub_cache()->GenerateProbe(masm, Code::LOAD_IC, code_flags,
                                                false, receiver, name, feedback,
-                                               scratch1, r8, r9);
+                                               receiver_map, scratch1, r9);
 
   __ bind(&miss);
   LoadIC::GenerateMiss(masm);
+
+
+  __ bind(&load_smi_map);
+  __ LoadRoot(receiver_map, Heap::kHeapNumberMapRootIndex);
+  __ jmp(&compare_map);
 }
 
 
@@ -4538,30 +4519,31 @@ void VectorRawKeyedLoadStub::GenerateImpl(MacroAssembler* masm, bool in_frame) {
   Register vector = VectorLoadICDescriptor::VectorRegister();      // r3
   Register slot = VectorLoadICDescriptor::SlotRegister();          // r0
   Register feedback = r4;
-  Register scratch1 = r5;
+  Register receiver_map = r5;
+  Register scratch1 = r8;
 
   __ add(feedback, vector, Operand::PointerOffsetFromSmiKey(slot));
   __ ldr(feedback, FieldMemOperand(feedback, FixedArray::kHeaderSize));
 
-  // Is it a weak cell?
-  Label try_array;
-  Label not_array, smi_key, key_okay, miss;
-  __ ldr(scratch1, FieldMemOperand(feedback, HeapObject::kMapOffset));
-  __ CompareRoot(scratch1, Heap::kWeakCellMapRootIndex);
-  __ b(ne, &try_array);
-  HandleMonomorphicCase(masm, receiver, key, vector, slot, feedback, scratch1,
-                        &miss);
+  // Try to quickly handle the monomorphic case without knowing for sure
+  // if we have a weak cell in feedback. We do know it's safe to look
+  // at WeakCell::kValueOffset.
+  Label try_array, load_smi_map, compare_map;
+  Label not_array, miss;
+  HandleMonomorphicCase(masm, receiver, receiver_map, feedback, vector, slot,
+                        scratch1, &compare_map, &load_smi_map, &try_array);
 
   __ bind(&try_array);
   // Is it a fixed array?
+  __ ldr(scratch1, FieldMemOperand(feedback, HeapObject::kMapOffset));
   __ CompareRoot(scratch1, Heap::kFixedArrayMapRootIndex);
   __ b(ne, &not_array);
 
   // We have a polymorphic element handler.
   Label polymorphic, try_poly_name;
   __ bind(&polymorphic);
-  HandleArrayCases(masm, receiver, key, vector, slot, feedback, scratch1, r8,
-                   r9, true, &miss);
+  HandleArrayCases(masm, receiver, key, vector, slot, feedback, receiver_map,
+                   scratch1, r9, true, &miss);
 
   __ bind(&not_array);
   // Is it generic?
@@ -4580,11 +4562,15 @@ void VectorRawKeyedLoadStub::GenerateImpl(MacroAssembler* masm, bool in_frame) {
   __ add(feedback, vector, Operand::PointerOffsetFromSmiKey(slot));
   __ ldr(feedback,
          FieldMemOperand(feedback, FixedArray::kHeaderSize + kPointerSize));
-  HandleArrayCases(masm, receiver, key, vector, slot, feedback, scratch1, r8,
-                   r9, false, &miss);
+  HandleArrayCases(masm, receiver, key, vector, slot, feedback, receiver_map,
+                   scratch1, r9, false, &miss);
 
   __ bind(&miss);
   KeyedLoadIC::GenerateMiss(masm);
+
+  __ bind(&load_smi_map);
+  __ LoadRoot(receiver_map, Heap::kHeapNumberMapRootIndex);
+  __ jmp(&compare_map);
 }
 
 

src/arm64/code-stubs-arm64.cc

@@ -4502,21 +4502,16 @@ void VectorRawLoadStub::GenerateForTrampoline(MacroAssembler* masm) {
 
 static void HandleArrayCases(MacroAssembler* masm, Register receiver,
                              Register key, Register vector, Register slot,
-                             Register feedback, Register scratch1,
-                             Register scratch2, Register scratch3,
+                             Register feedback, Register receiver_map,
+                             Register scratch1, Register scratch2,
                              bool is_polymorphic, Label* miss) {
   // feedback initially contains the feedback array
   Label next_loop, prepare_next;
   Label load_smi_map, compare_map;
   Label start_polymorphic;
 
-  Register receiver_map = scratch1;
-  Register cached_map = scratch2;
+  Register cached_map = scratch1;
 
-  // Receiver might not be a heap object.
-  __ JumpIfSmi(receiver, &load_smi_map);
-  __ Ldr(receiver_map, FieldMemOperand(receiver, HeapObject::kMapOffset));
-  __ Bind(&compare_map);
   __ Ldr(cached_map,
          FieldMemOperand(feedback, FixedArray::OffsetOfElementAt(0)));
   __ Ldr(cached_map, FieldMemOperand(cached_map, WeakCell::kValueOffset));
@@ -4528,7 +4523,7 @@ static void HandleArrayCases(MacroAssembler* masm, Register receiver,
   __ Add(handler, handler, Code::kHeaderSize - kHeapObjectTag);
   __ Jump(feedback);
 
-  Register length = scratch3;
+  Register length = scratch2;
   __ Bind(&start_polymorphic);
   __ Ldr(length, FieldMemOperand(feedback, FixedArray::kLengthOffset));
   if (!is_polymorphic) {
@@ -4546,9 +4541,9 @@ static void HandleArrayCases(MacroAssembler* masm, Register receiver,
   //                              ^              ^
   //                              |              |
   //                         pointer_reg      too_far
-  //                         aka feedback     scratch3
-  // also need receiver_map (aka scratch1)
-  // use cached_map (scratch2) to look in the weak map values.
+  //                         aka feedback     scratch2
+  // also need receiver_map
+  // use cached_map (scratch1) to look in the weak map values.
   __ Add(too_far, feedback,
          Operand::UntagSmiAndScale(length, kPointerSizeLog2));
   __ Add(too_far, too_far, FixedArray::kHeaderSize - kHeapObjectTag);
@@ -4571,43 +4566,24 @@ static void HandleArrayCases(MacroAssembler* masm, Register receiver,
 
   // We exhausted our array of map handler pairs.
   __ jmp(miss);
-
-  __ Bind(&load_smi_map);
-  __ LoadRoot(receiver_map, Heap::kHeapNumberMapRootIndex);
-  __ jmp(&compare_map);
 }
 
 
 static void HandleMonomorphicCase(MacroAssembler* masm, Register receiver,
-                                  Register key, Register vector, Register slot,
-                                  Register weak_cell, Register scratch,
-                                  Label* miss) {
-  // feedback initially contains the feedback array
-  Label compare_smi_map;
-  Register receiver_map = scratch;
-  Register cached_map = weak_cell;
-
-  // Move the weak map into the weak_cell register.
-  __ Ldr(cached_map, FieldMemOperand(weak_cell, WeakCell::kValueOffset));
-
-  // Receiver might not be a heap object.
-  __ JumpIfSmi(receiver, &compare_smi_map);
+                                  Register receiver_map, Register feedback,
+                                  Register vector, Register slot,
+                                  Register scratch, Label* compare_map,
+                                  Label* load_smi_map, Label* try_array) {
+  __ JumpIfSmi(receiver, load_smi_map);
   __ Ldr(receiver_map, FieldMemOperand(receiver, HeapObject::kMapOffset));
+  __ bind(compare_map);
+  Register cached_map = scratch;
+  // Move the weak map into the weak_cell register.
+  __ Ldr(cached_map, FieldMemOperand(feedback, WeakCell::kValueOffset));
   __ Cmp(cached_map, receiver_map);
-  __ B(ne, miss);
-
-  Register handler = weak_cell;
-  __ Add(handler, vector, Operand::UntagSmiAndScale(slot, kPointerSizeLog2));
-  __ Ldr(handler,
-         FieldMemOperand(handler, FixedArray::kHeaderSize + kPointerSize));
-  __ Add(handler, handler, Code::kHeaderSize - kHeapObjectTag);
-  __ Jump(weak_cell);
+  __ B(ne, try_array);
 
-  // In microbenchmarks, it made sense to unroll this code so that the call to
-  // the handler is duplicated for a HeapObject receiver and a Smi receiver.
-  // TODO(mvstanton): does this hold on ARM?
-  __ Bind(&compare_smi_map);
-  __ JumpIfNotRoot(weak_cell, Heap::kHeapNumberMapRootIndex, miss);
+  Register handler = feedback;
   __ Add(handler, vector, Operand::UntagSmiAndScale(slot, kPointerSizeLog2));
   __ Ldr(handler,
          FieldMemOperand(handler, FixedArray::kHeaderSize + kPointerSize));
@@ -4622,24 +4598,26 @@ void VectorRawLoadStub::GenerateImpl(MacroAssembler* masm, bool in_frame) {
   Register vector = VectorLoadICDescriptor::VectorRegister();      // x3
   Register slot = VectorLoadICDescriptor::SlotRegister();          // x0
   Register feedback = x4;
-  Register scratch1 = x5;
+  Register receiver_map = x5;
+  Register scratch1 = x6;
 
   __ Add(feedback, vector, Operand::UntagSmiAndScale(slot, kPointerSizeLog2));
   __ Ldr(feedback, FieldMemOperand(feedback, FixedArray::kHeaderSize));
 
-  // Is it a weak cell?
-  Label try_array;
-  Label not_array, smi_key, key_okay, miss;
-  __ Ldr(scratch1, FieldMemOperand(feedback, HeapObject::kMapOffset));
-  __ JumpIfNotRoot(scratch1, Heap::kWeakCellMapRootIndex, &try_array);
-  HandleMonomorphicCase(masm, receiver, name, vector, slot, feedback, scratch1,
-                        &miss);
+  // Try to quickly handle the monomorphic case without knowing for sure
+  // if we have a weak cell in feedback. We do know it's safe to look
+  // at WeakCell::kValueOffset.
+  Label try_array, load_smi_map, compare_map;
+  Label not_array, miss;
+  HandleMonomorphicCase(masm, receiver, receiver_map, feedback, vector, slot,
+                        scratch1, &compare_map, &load_smi_map, &try_array);
 
   // Is it a fixed array?
   __ Bind(&try_array);
+  __ Ldr(scratch1, FieldMemOperand(feedback, HeapObject::kMapOffset));
   __ JumpIfNotRoot(scratch1, Heap::kFixedArrayMapRootIndex, &not_array);
-  HandleArrayCases(masm, receiver, name, vector, slot, feedback, scratch1, x6,
-                   x7, true, &miss);
+  HandleArrayCases(masm, receiver, name, vector, slot, feedback, receiver_map,
+                   scratch1, x7, true, &miss);
 
   __ Bind(&not_array);
   __ JumpIfNotRoot(feedback, Heap::kmegamorphic_symbolRootIndex, &miss);
@@ -4647,10 +4625,14 @@ void VectorRawLoadStub::GenerateImpl(MacroAssembler* masm, bool in_frame) {
       Code::ComputeHandlerFlags(Code::LOAD_IC));
   masm->isolate()->stub_cache()->GenerateProbe(masm, Code::LOAD_IC, code_flags,
                                                false, receiver, name, feedback,
-                                               scratch1, x6, x7);
+                                               receiver_map, scratch1, x7);
 
   __ Bind(&miss);
   LoadIC::GenerateMiss(masm);
+
+  __ Bind(&load_smi_map);
+  __ LoadRoot(receiver_map, Heap::kHeapNumberMapRootIndex);
+  __ jmp(&compare_map);
 }
 
 
@@ -4670,28 +4652,30 @@ void VectorRawKeyedLoadStub::GenerateImpl(MacroAssembler* masm, bool in_frame) {
   Register vector = VectorLoadICDescriptor::VectorRegister();      // x3
   Register slot = VectorLoadICDescriptor::SlotRegister();          // x0
   Register feedback = x4;
-  Register scratch1 = x5;
+  Register receiver_map = x5;
+  Register scratch1 = x6;
 
   __ Add(feedback, vector, Operand::UntagSmiAndScale(slot, kPointerSizeLog2));
   __ Ldr(feedback, FieldMemOperand(feedback, FixedArray::kHeaderSize));
 
-  // Is it a weak cell?
-  Label try_array;
-  Label not_array, smi_key, key_okay, miss;
-  __ Ldr(scratch1, FieldMemOperand(feedback, HeapObject::kMapOffset));
-  __ JumpIfNotRoot(scratch1, Heap::kWeakCellMapRootIndex, &try_array);
-  HandleMonomorphicCase(masm, receiver, key, vector, slot, feedback, scratch1,
-                        &miss);
+  // Try to quickly handle the monomorphic case without knowing for sure
+  // if we have a weak cell in feedback. We do know it's safe to look
+  // at WeakCell::kValueOffset.
+  Label try_array, load_smi_map, compare_map;
+  Label not_array, miss;
+  HandleMonomorphicCase(masm, receiver, receiver_map, feedback, vector, slot,
+                        scratch1, &compare_map, &load_smi_map, &try_array);
 
   __ Bind(&try_array);
   // Is it a fixed array?
+  __ Ldr(scratch1, FieldMemOperand(feedback, HeapObject::kMapOffset));
   __ JumpIfNotRoot(scratch1, Heap::kFixedArrayMapRootIndex, &not_array);
 
   // We have a polymorphic element handler.
   Label polymorphic, try_poly_name;
   __ Bind(&polymorphic);
-  HandleArrayCases(masm, receiver, key, vector, slot, feedback, scratch1, x6,
-                   x7, true, &miss);
+  HandleArrayCases(masm, receiver, key, vector, slot, feedback, receiver_map,
+                   scratch1, x7, true, &miss);
 
   __ Bind(&not_array);
   // Is it generic?
@@ -4710,11 +4694,15 @@ void VectorRawKeyedLoadStub::GenerateImpl(MacroAssembler* masm, bool in_frame) {
   __ Add(feedback, vector, Operand::UntagSmiAndScale(slot, kPointerSizeLog2));
   __ Ldr(feedback,
          FieldMemOperand(feedback, FixedArray::kHeaderSize + kPointerSize));
-  HandleArrayCases(masm, receiver, key, vector, slot, feedback, scratch1, x6,
-                   x7, false, &miss);
+  HandleArrayCases(masm, receiver, key, vector, slot, feedback, receiver_map,
+                   scratch1, x7, false, &miss);
 
   __ Bind(&miss);
   KeyedLoadIC::GenerateMiss(masm);
+
+  __ Bind(&load_smi_map);
+  __ LoadRoot(receiver_map, Heap::kHeapNumberMapRootIndex);
+  __ jmp(&compare_map);
 }
 
 

src/x64/code-stubs-x64.cc

@@ -4351,24 +4351,18 @@ void KeyedLoadICTrampolineStub::Generate(MacroAssembler* masm) {
 
 static void HandleArrayCases(MacroAssembler* masm, Register receiver,
                              Register key, Register vector, Register slot,
-                             Register feedback, Register scratch1,
-                             Register scratch2, Register scratch3,
-                             Register scratch4, bool is_polymorphic,
+                             Register feedback, Register receiver_map,
+                             Register scratch1, Register scratch2,
+                             Register scratch3, bool is_polymorphic,
                              Label* miss) {
   // feedback initially contains the feedback array
   Label next_loop, prepare_next;
-  Label load_smi_map, compare_map;
   Label start_polymorphic;
 
-  Register receiver_map = scratch1;
-  Register counter = scratch2;
-  Register length = scratch3;
-  Register cached_map = scratch4;
+  Register counter = scratch1;
+  Register length = scratch2;
+  Register cached_map = scratch3;
 
-  // Receiver might not be a heap object.
-  __ JumpIfSmi(receiver, &load_smi_map);
-  __ movp(receiver_map, FieldOperand(receiver, 0));
-  __ bind(&compare_map);
   __ movp(cached_map, FieldOperand(feedback, FixedArray::OffsetOfElementAt(0)));
   __ cmpp(receiver_map, FieldOperand(cached_map, WeakCell::kValueOffset));
   __ j(not_equal, &start_polymorphic);
@@ -4407,39 +4401,21 @@ static void HandleArrayCases(MacroAssembler* masm, Register receiver,
 
   // We exhausted our array of map handler pairs.
   __ jmp(miss);
-
-  __ bind(&load_smi_map);
-  __ LoadRoot(receiver_map, Heap::kHeapNumberMapRootIndex);
-  __ jmp(&compare_map);
 }
 
 
 static void HandleMonomorphicCase(MacroAssembler* masm, Register receiver,
-                                  Register key, Register vector, Register slot,
-                                  Register weak_cell, Register integer_slot,
-                                  Label* miss) {
-  // feedback initially contains the feedback array
-  Label compare_smi_map;
-
-  // Move the weak map into the weak_cell register.
-  Register ic_map = weak_cell;
-  __ movp(ic_map, FieldOperand(weak_cell, WeakCell::kValueOffset));
-
-  // Receiver might not be a heap object.
-  __ JumpIfSmi(receiver, &compare_smi_map);
-  __ cmpp(ic_map, FieldOperand(receiver, 0));
-  __ j(not_equal, miss);
-  Register handler = weak_cell;
-  __ movp(handler, FieldOperand(vector, integer_slot, times_pointer_size,
-                                FixedArray::kHeaderSize + kPointerSize));
-  __ leap(handler, FieldOperand(handler, Code::kHeaderSize));
-  __ jmp(handler);
+                                  Register receiver_map, Register feedback,
+                                  Register vector, Register integer_slot,
+                                  Label* compare_map, Label* load_smi_map,
+                                  Label* try_array) {
+  __ JumpIfSmi(receiver, load_smi_map);
+  __ movp(receiver_map, FieldOperand(receiver, 0));
 
-  // In microbenchmarks, it made sense to unroll this code so that the call to
-  // the handler is duplicated for a HeapObject receiver and a Smi receiver.
-  __ bind(&compare_smi_map);
-  __ CompareRoot(ic_map, Heap::kHeapNumberMapRootIndex);
-  __ j(not_equal, miss);
+  __ bind(compare_map);
+  __ cmpp(receiver_map, FieldOperand(feedback, WeakCell::kValueOffset));
+  __ j(not_equal, try_array);
+  Register handler = feedback;
   __ movp(handler, FieldOperand(vector, integer_slot, times_pointer_size,
                                 FixedArray::kHeaderSize + kPointerSize));
   __ leap(handler, FieldOperand(handler, Code::kHeaderSize));
@@ -4464,25 +4440,26 @@ void VectorRawLoadStub::GenerateImpl(MacroAssembler* masm, bool in_frame) {
   Register slot = VectorLoadICDescriptor::SlotRegister();          // rax
   Register feedback = rdi;
   Register integer_slot = r8;
+  Register receiver_map = r9;
 
   __ SmiToInteger32(integer_slot, slot);
   __ movp(feedback, FieldOperand(vector, integer_slot, times_pointer_size,
                                  FixedArray::kHeaderSize));
 
-  // Is it a weak cell?
-  Label try_array;
-  Label not_array, smi_key, key_okay, miss;
-  __ CompareRoot(FieldOperand(feedback, 0), Heap::kWeakCellMapRootIndex);
-  __ j(not_equal, &try_array);
-  HandleMonomorphicCase(masm, receiver, name, vector, slot, feedback,
-                        integer_slot, &miss);
+  // Try to quickly handle the monomorphic case without knowing for sure
+  // if we have a weak cell in feedback. We do know it's safe to look
+  // at WeakCell::kValueOffset.
+  Label try_array, load_smi_map, compare_map;
+  Label not_array, miss;
+  HandleMonomorphicCase(masm, receiver, receiver_map, feedback, vector,
+                        integer_slot, &compare_map, &load_smi_map, &try_array);
 
   // Is it a fixed array?
   __ bind(&try_array);
   __ CompareRoot(FieldOperand(feedback, 0), Heap::kFixedArrayMapRootIndex);
   __ j(not_equal, &not_array);
-  HandleArrayCases(masm, receiver, name, vector, slot, feedback, integer_slot,
-                   r9, r11, r15, true, &miss);
+  HandleArrayCases(masm, receiver, name, vector, slot, feedback, receiver_map,
+                   integer_slot, r11, r15, true, &miss);
 
   __ bind(&not_array);
   __ CompareRoot(feedback, Heap::kmegamorphic_symbolRootIndex);
@@ -4494,6 +4471,10 @@ void VectorRawLoadStub::GenerateImpl(MacroAssembler* masm, bool in_frame) {
 
   __ bind(&miss);
   LoadIC::GenerateMiss(masm);
+
+  __ bind(&load_smi_map);
+  __ LoadRoot(receiver_map, Heap::kHeapNumberMapRootIndex);
+  __ jmp(&compare_map);
 }
 
 
@@ -4514,18 +4495,19 @@ void VectorRawKeyedLoadStub::GenerateImpl(MacroAssembler* masm, bool in_frame) {
   Register slot = VectorLoadICDescriptor::SlotRegister();          // rax
   Register feedback = rdi;
   Register integer_slot = r8;
+  Register receiver_map = r9;
 
   __ SmiToInteger32(integer_slot, slot);
   __ movp(feedback, FieldOperand(vector, integer_slot, times_pointer_size,
                                  FixedArray::kHeaderSize));
 
-  // Is it a weak cell?
-  Label try_array;
-  Label not_array, smi_key, key_okay, miss;
-  __ CompareRoot(FieldOperand(feedback, 0), Heap::kWeakCellMapRootIndex);
-  __ j(not_equal, &try_array);
-  HandleMonomorphicCase(masm, receiver, key, vector, slot, feedback,
-                        integer_slot, &miss);
+  // Try to quickly handle the monomorphic case without knowing for sure
+  // if we have a weak cell in feedback. We do know it's safe to look
+  // at WeakCell::kValueOffset.
+  Label try_array, load_smi_map, compare_map;
+  Label not_array, miss;
+  HandleMonomorphicCase(masm, receiver, receiver_map, feedback, vector,
+                        integer_slot, &compare_map, &load_smi_map, &try_array);
 
   __ bind(&try_array);
   // Is it a fixed array?
@@ -4535,8 +4517,8 @@ void VectorRawKeyedLoadStub::GenerateImpl(MacroAssembler* masm, bool in_frame) {
   // We have a polymorphic element handler.
   Label polymorphic, try_poly_name;
   __ bind(&polymorphic);
-  HandleArrayCases(masm, receiver, key, vector, slot, feedback, integer_slot,
-                   r9, r11, r15, true, &miss);
+  HandleArrayCases(masm, receiver, key, vector, slot, feedback, receiver_map,
+                   integer_slot, r11, r15, true, &miss);
 
   __ bind(&not_array);
   // Is it generic?
@@ -4554,11 +4536,15 @@ void VectorRawKeyedLoadStub::GenerateImpl(MacroAssembler* masm, bool in_frame) {
   // at least one map/handler pair.
   __ movp(feedback, FieldOperand(vector, integer_slot, times_pointer_size,
                                  FixedArray::kHeaderSize + kPointerSize));
-  HandleArrayCases(masm, receiver, key, vector, slot, feedback, integer_slot,
-                   r9, r11, r15, false, &miss);
+  HandleArrayCases(masm, receiver, key, vector, slot, feedback, receiver_map,
+                   integer_slot, r11, r15, false, &miss);
 
   __ bind(&miss);
   KeyedLoadIC::GenerateMiss(masm);
+
+  __ bind(&load_smi_map);
+  __ LoadRoot(receiver_map, Heap::kHeapNumberMapRootIndex);
+  __ jmp(&compare_map);
 }