[arm] Clean up disabling of sharing code target entries.

This fixes an issue with ful-codegen where code target entries for the OSR
check were being incorrectly shared. We now explicitly disable sharing of code
target constant pool entries for full-codegen and for calls to builtins from
WASM code, using a scope.

BUG=chromium:725743

Review-Url: https://codereview.chromium.org/2922433002
Cr-Commit-Position: refs/heads/master@{#45661}

src/arm/assembler-arm.cc

@@ -557,6 +557,7 @@ Assembler::Assembler(IsolateData isolate_data, void* buffer, int buffer_size)
   pending_64_bit_constants_.reserve(kMinNumPendingConstants);
   reloc_info_writer.Reposition(buffer_ + buffer_size_, pc_);
   next_buffer_check_ = 0;
+  code_target_sharing_blocked_nesting_ = 0;
   const_pool_blocked_nesting_ = 0;
   no_const_pool_before_ = 0;
   first_const_pool_32_use_ = -1;
@@ -573,7 +574,8 @@ Assembler::Assembler(IsolateData isolate_data, void* buffer, int buffer_size)
 
 
 Assembler::~Assembler() {
-  DCHECK(const_pool_blocked_nesting_ == 0);
+  DCHECK_EQ(const_pool_blocked_nesting_, 0);
+  DCHECK_EQ(code_target_sharing_blocked_nesting_, 0);
 }
 
 void Assembler::GetCode(Isolate* isolate, CodeDesc* desc) {
@@ -5055,9 +5057,9 @@ void Assembler::ConstantPoolAddEntry(int position, RelocInfo::Mode rmode,
   if (pending_32_bit_constants_.empty()) {
     first_const_pool_32_use_ = position;
   }
-  ConstantPoolEntry entry(
-      position, value,
-      sharing_ok || (rmode == RelocInfo::CODE_TARGET && serializer_enabled()));
+  ConstantPoolEntry entry(position, value,
+                          sharing_ok || (rmode == RelocInfo::CODE_TARGET &&
+                                         IsCodeTargetSharingAllowed()));
 
   bool shared = false;
   if (sharing_ok) {
@@ -5073,10 +5075,7 @@ void Assembler::ConstantPoolAddEntry(int position, RelocInfo::Mode rmode,
     }
   }
 
-  if (rmode == RelocInfo::CODE_TARGET && serializer_enabled()) {
-    // TODO(all): We only do this in the serializer, for now, because
-    // full-codegen relies on RelocInfo for translating PCs between full-codegen
-    // normal and debug code.
+  if (rmode == RelocInfo::CODE_TARGET && IsCodeTargetSharingAllowed()) {
     // Sharing entries here relies on canonicalized handles - without them, we
     // will miss the optimisation opportunity.
     Address handle_address = reinterpret_cast<Address>(value);

src/arm/assembler-arm.h

@@ -1509,6 +1509,36 @@ class Assembler : public AssemblerBase {
     DISALLOW_IMPLICIT_CONSTRUCTORS(BlockConstPoolScope);
   };
 
+  // Class for blocking sharing of code targets in constant pool.
+  class BlockCodeTargetSharingScope {
+   public:
+    explicit BlockCodeTargetSharingScope(Assembler* assem) : assem_(nullptr) {
+      Open(assem);
+    }
+    // This constructor does not initialize the scope. The user needs to
+    // explicitly call Open() before using it.
+    BlockCodeTargetSharingScope() : assem_(nullptr) {}
+    ~BlockCodeTargetSharingScope() {
+      Close();
+    }
+    void Open(Assembler* assem) {
+      DCHECK_NULL(assem_);
+      DCHECK_NOT_NULL(assem);
+      assem_ = assem;
+      assem_->StartBlockCodeTargetSharing();
+    }
+
+   private:
+    void Close() {
+      if (assem_ != nullptr) {
+        assem_->EndBlockCodeTargetSharing();
+      }
+    }
+    Assembler* assem_;
+
+    DISALLOW_COPY_AND_ASSIGN(BlockCodeTargetSharingScope);
+  };
+
   // Debugging
 
   // Mark address of a debug break slot.
@@ -1675,8 +1705,22 @@ class Assembler : public AssemblerBase {
   // Patch branch instruction at pos to branch to given branch target pos
   void target_at_put(int pos, int target_pos);
 
+  // Prevent sharing of code target constant pool entries until
+  // EndBlockCodeTargetSharing is called. Calls to this function can be nested
+  // but must be followed by an equal number of call to
+  // EndBlockCodeTargetSharing.
+  void StartBlockCodeTargetSharing() {
+    ++code_target_sharing_blocked_nesting_;
+  }
+
+  // Resume sharing of constant pool code target entries. Needs to be called
+  // as many times as StartBlockCodeTargetSharing to have an effect.
+  void EndBlockCodeTargetSharing() {
+    --code_target_sharing_blocked_nesting_;
+  }
+
   // Prevent contant pool emission until EndBlockConstPool is called.
-  // Call to this function can be nested but must be followed by an equal
+  // Calls to this function can be nested but must be followed by an equal
   // number of call to EndBlockConstpool.
   void StartBlockConstPool() {
     if (const_pool_blocked_nesting_++ == 0) {
@@ -1686,7 +1730,7 @@ class Assembler : public AssemblerBase {
     }
   }
 
-  // Resume constant pool emission. Need to be called as many time as
+  // Resume constant pool emission. Needs to be called as many times as
   // StartBlockConstPool to have an effect.
   void EndBlockConstPool() {
     if (--const_pool_blocked_nesting_ == 0) {
@@ -1778,6 +1822,11 @@ class Assembler : public AssemblerBase {
   static constexpr int kCheckPoolIntervalInst = 32;
   static constexpr int kCheckPoolInterval = kCheckPoolIntervalInst * kInstrSize;
 
+  // Sharing of code target entries may be blocked in some code sequences.
+  int code_target_sharing_blocked_nesting_;
+  bool IsCodeTargetSharingAllowed() const {
+    return code_target_sharing_blocked_nesting_ == 0;
+  }
 
   // Emission of the constant pool may be blocked in some code sequences.
   int const_pool_blocked_nesting_;  // Block emission if this is not zero.
@@ -1820,6 +1869,7 @@ class Assembler : public AssemblerBase {
   friend class RelocInfo;
   friend class CodePatcher;
   friend class BlockConstPoolScope;
+  friend class BlockCodeTargetSharingScope;
   friend class EnsureSpace;
 };
 

src/compiler/arm/code-generator-arm.cc

@@ -690,6 +690,11 @@ CodeGenerator::CodeGenResult CodeGenerator::AssembleArchInstruction(
   ArchOpcode arch_opcode = ArchOpcodeField::decode(opcode);
   switch (arch_opcode) {
     case kArchCallCodeObject: {
+      // We must not share code targets for calls to builtins for WASM code, as
+      // they might need to be patched individually.
+      internal::Assembler::BlockCodeTargetSharingScope scope;
+      if (info()->IsWasm()) scope.Open(masm());
+
       EnsureSpaceForLazyDeopt();
       if (instr->InputAt(0)->IsImmediate()) {
         __ Call(Handle<Code>::cast(i.InputHeapObject(0)),
@@ -706,6 +711,11 @@ CodeGenerator::CodeGenResult CodeGenerator::AssembleArchInstruction(
     }
     case kArchTailCallCodeObjectFromJSFunction:
     case kArchTailCallCodeObject: {
+      // We must not share code targets for calls to builtins for WASM code, as
+      // they might need to be patched individually.
+      internal::Assembler::BlockCodeTargetSharingScope scope;
+      if (info()->IsWasm()) scope.Open(masm());
+
       if (arch_opcode == kArchTailCallCodeObjectFromJSFunction) {
         AssemblePopArgumentsAdaptorFrame(kJavaScriptCallArgCountRegister,
                                          i.TempRegister(0), i.TempRegister(1),

src/full-codegen/arm/full-codegen-arm.cc

@@ -109,6 +109,10 @@ class JumpPatchSite BASE_EMBEDDED {
 // frames-arm.h for its layout.
 void FullCodeGenerator::Generate() {
   CompilationInfo* info = info_;
+  // Block sharing of code target entries. The interrupt checks must be
+  // possible to patch individually, and replacing code with a debug version
+  // relies on RelocInfo not being shared.
+  Assembler::BlockCodeTargetSharingScope block_code_target_sharing(masm_);
   profiling_counter_ = isolate()->factory()->NewCell(
       Handle<Smi>(Smi::FromInt(FLAG_interrupt_budget), isolate()));
   SetFunctionPosition(literal());

test/mjsunit/compiler/regress-725743.js

@@ -0,0 +1,16 @@
+// Copyright 2017 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// Flags: --no-turbo --cache=code --no-lazy
+
+function f() {
+  var n = a.length;
+  for (var i = 0; i < n; i++) {
+  }
+  for (var i = 0; i < n; i++) {
+  }
+}
+var a = "xxxxxxxxxxxxxxxxxxxxxxxxx";
+while (a.length < 100000) a = a + a;
+f();