src/v8/src/wasm/function-body-decoder.cc

// Copyright 2015 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.

#include "src/signature.h"

#include "src/base/platform/elapsed-timer.h"
#include "src/flags.h"
#include "src/handles.h"
#include "src/objects-inl.h"
#include "src/zone/zone-containers.h"

#include "src/wasm/decoder.h"
#include "src/wasm/function-body-decoder-impl.h"
#include "src/wasm/function-body-decoder.h"
#include "src/wasm/wasm-limits.h"
#include "src/wasm/wasm-module.h"
#include "src/wasm/wasm-opcodes.h"

#include "src/ostreams.h"

#include "src/compiler/wasm-compiler.h"

namespace v8 {
namespace internal {
namespace wasm {

namespace {

// An SsaEnv environment carries the current local variable renaming
// as well as the current effect and control dependency in the TF graph.
// It maintains a control state that tracks whether the environment
// is reachable, has reached a control end, or has been merged.
struct SsaEnv {
  enum State { kControlEnd, kUnreachable, kReached, kMerged };

  State state;
  TFNode* control;
  TFNode* effect;
  compiler::WasmContextCacheNodes context_cache;
  TFNode** locals;

  bool go() { return state >= kReached; }
  void Kill(State new_state = kControlEnd) {
    state = new_state;
    locals = nullptr;
    control = nullptr;
    effect = nullptr;
    context_cache = {0};
  }
  void SetNotMerged() {
    if (state == kMerged) state = kReached;
  }
};

#define BUILD(func, ...)                                            \
  ([&] {                                                            \
    DCHECK(ssa_env_->go());                                         \
    DCHECK(decoder->ok());                                          \
    return CheckForException(decoder, builder_->func(__VA_ARGS__)); \
  })()

constexpr uint32_t kNullCatch = static_cast<uint32_t>(-1);

class WasmGraphBuildingInterface {
 public:
  static constexpr wasm::Decoder::ValidateFlag validate =
      wasm::Decoder::kValidate;
  using Decoder = WasmFullDecoder<validate, WasmGraphBuildingInterface>;

  struct Value : public ValueWithNamedConstructors<Value> {
    TFNode* node;
  };

  struct TryInfo : public ZoneObject {
    SsaEnv* catch_env;
    TFNode* exception;

    explicit TryInfo(SsaEnv* c) : catch_env(c), exception(nullptr) {}
  };

  struct Control : public ControlWithNamedConstructors<Control, Value> {
    SsaEnv* end_env;         // end environment for the construct.
    SsaEnv* false_env;       // false environment (only for if).
    TryInfo* try_info;       // information used for compiling try statements.
    int32_t previous_catch;  // previous Control (on the stack) with a catch.
  };

  explicit WasmGraphBuildingInterface(TFBuilder* builder) : builder_(builder) {}

  void StartFunction(Decoder* decoder) {
    SsaEnv* ssa_env =
        reinterpret_cast<SsaEnv*>(decoder->zone()->New(sizeof(SsaEnv)));
    uint32_t num_locals = decoder->NumLocals();
    uint32_t env_count = num_locals;
    size_t size = sizeof(TFNode*) * env_count;
    ssa_env->state = SsaEnv::kReached;
    ssa_env->locals =
        size > 0 ? reinterpret_cast<TFNode**>(decoder->zone()->New(size))
                 : nullptr;

    // The first '+ 1' is needed by TF Start node, the second '+ 1' is for the
    // wasm_context parameter.
    TFNode* start = builder_->Start(
        static_cast<int>(decoder->sig_->parameter_count() + 1 + 1));
    // Initialize the wasm_context (the paramater at index 0).
    builder_->set_wasm_context(
        builder_->Param(compiler::kWasmContextParameterIndex));
    // Initialize local variables. Parameters are shifted by 1 because of the
    // the wasm_context.
    uint32_t index = 0;
    for (; index < decoder->sig_->parameter_count(); ++index) {
      ssa_env->locals[index] = builder_->Param(index + 1);
    }
    while (index < num_locals) {
      ValueType type = decoder->GetLocalType(index);
      TFNode* node = DefaultValue(type);
      while (index < num_locals && decoder->GetLocalType(index) == type) {
        // Do a whole run of like-typed locals at a time.
        ssa_env->locals[index++] = node;
      }
    }
    ssa_env->effect = start;
    ssa_env->control = start;
    // Initialize effect and control before loading the context.
    builder_->set_effect_ptr(&ssa_env->effect);
    builder_->set_control_ptr(&ssa_env->control);
    LoadContextIntoSsa(ssa_env);
    SetEnv(ssa_env);
  }

  // Reload the wasm context variables from the WasmContext structure attached
  // to the memory object into the Ssa Environment.
  void LoadContextIntoSsa(SsaEnv* ssa_env) {
    if (!ssa_env || !ssa_env->go()) return;
    builder_->InitContextCache(&ssa_env->context_cache);
  }

  void StartFunctionBody(Decoder* decoder, Control* block) {
    SsaEnv* break_env = ssa_env_;
    SetEnv(Steal(decoder->zone(), break_env));
    block->end_env = break_env;
  }

  void FinishFunction(Decoder*) { builder_->PatchInStackCheckIfNeeded(); }

  void OnFirstError(Decoder*) {}

  void NextInstruction(Decoder*, WasmOpcode) {}

  void Block(Decoder* decoder, Control* block) {
    // The break environment is the outer environment.
    block->end_env = ssa_env_;
    SetEnv(Steal(decoder->zone(), ssa_env_));
  }

  void Loop(Decoder* decoder, Control* block) {
    SsaEnv* finish_try_env = Steal(decoder->zone(), ssa_env_);
    block->end_env = finish_try_env;
    // The continue environment is the inner environment.
    SetEnv(PrepareForLoop(decoder, finish_try_env));
    ssa_env_->SetNotMerged();
    if (!decoder->ok()) return;
    // Wrap input merge into phis.
    for (unsigned i = 0; i < block->start_merge.arity; ++i) {
      Value& val = block->start_merge[i];
      val.node = builder_->Phi(val.type, 1, &val.node, block->end_env->control);
    }
  }

  void Try(Decoder* decoder, Control* block) {
    SsaEnv* outer_env = ssa_env_;
    SsaEnv* catch_env = Split(decoder, outer_env);
    // Mark catch environment as unreachable, since only accessable
    // through catch unwinding (i.e. landing pads).
    catch_env->state = SsaEnv::kUnreachable;
    SsaEnv* try_env = Steal(decoder->zone(), outer_env);
    SetEnv(try_env);
    TryInfo* try_info = new (decoder->zone()) TryInfo(catch_env);
    block->end_env = outer_env;
    block->try_info = try_info;
    block->previous_catch = current_catch_;
    current_catch_ = static_cast<int32_t>(decoder->control_depth() - 1);
  }

  void If(Decoder* decoder, const Value& cond, Control* if_block) {
    TFNode* if_true = nullptr;
    TFNode* if_false = nullptr;
    if (ssa_env_->go()) BUILD(BranchNoHint, cond.node, &if_true, &if_false);
    SsaEnv* end_env = ssa_env_;
    SsaEnv* false_env = Split(decoder, ssa_env_);
    false_env->control = if_false;
    SsaEnv* true_env = Steal(decoder->zone(), ssa_env_);
    true_env->control = if_true;
    if_block->end_env = end_env;
    if_block->false_env = false_env;
    SetEnv(true_env);
  }

  void FallThruTo(Decoder* decoder, Control* c) {
    DCHECK(!c->is_loop());
    MergeValuesInto(decoder, c, &c->end_merge);
  }

  void PopControl(Decoder* decoder, Control* block) {
    if (!block->is_loop()) SetEnv(block->end_env);
  }

  void EndControl(Decoder* decoder, Control* block) { ssa_env_->Kill(); }

  void UnOp(Decoder* decoder, WasmOpcode opcode, FunctionSig* sig,
            const Value& value, Value* result) {
    result->node = BUILD(Unop, opcode, value.node, decoder->position());
  }

  void BinOp(Decoder* decoder, WasmOpcode opcode, FunctionSig* sig,
             const Value& lhs, const Value& rhs, Value* result) {
    auto node = BUILD(Binop, opcode, lhs.node, rhs.node, decoder->position());
    if (result) result->node = node;
  }

  void I32Const(Decoder* decoder, Value* result, int32_t value) {
    result->node = builder_->Int32Constant(value);
  }

  void I64Const(Decoder* decoder, Value* result, int64_t value) {
    result->node = builder_->Int64Constant(value);
  }

  void F32Const(Decoder* decoder, Value* result, float value) {
    result->node = builder_->Float32Constant(value);
  }

  void F64Const(Decoder* decoder, Value* result, double value) {
    result->node = builder_->Float64Constant(value);
  }

  void Drop(Decoder* decoder, const Value& value) {}

  void DoReturn(Decoder* decoder, Vector<Value> values, bool implicit) {
    if (implicit) {
      DCHECK_EQ(1, decoder->control_depth());
      SetEnv(decoder->control_at(0)->end_env);
    }
    size_t num_values = values.size();
    TFNode** buffer = GetNodes(values);
    for (size_t i = 0; i < num_values; ++i) {
      buffer[i] = values[i].node;
    }
    BUILD(Return, static_cast<unsigned>(values.size()), buffer);
  }

  void GetLocal(Decoder* decoder, Value* result,
                const LocalIndexOperand<validate>& operand) {
    if (!ssa_env_->locals) return;  // unreachable
    result->node = ssa_env_->locals[operand.index];
  }

  void SetLocal(Decoder* decoder, const Value& value,
                const LocalIndexOperand<validate>& operand) {
    if (!ssa_env_->locals) return;  // unreachable
    ssa_env_->locals[operand.index] = value.node;
  }

  void TeeLocal(Decoder* decoder, const Value& value, Value* result,
                const LocalIndexOperand<validate>& operand) {
    result->node = value.node;
    if (!ssa_env_->locals) return;  // unreachable
    ssa_env_->locals[operand.index] = value.node;
  }

  void GetGlobal(Decoder* decoder, Value* result,
                 const GlobalIndexOperand<validate>& operand) {
    result->node = BUILD(GetGlobal, operand.index);
  }

  void SetGlobal(Decoder* decoder, const Value& value,
                 const GlobalIndexOperand<validate>& operand) {
    BUILD(SetGlobal, operand.index, value.node);
  }

  void Unreachable(Decoder* decoder) {
    BUILD(Unreachable, decoder->position());
  }

  void Select(Decoder* decoder, const Value& cond, const Value& fval,
              const Value& tval, Value* result) {
    TFNode* controls[2];
    BUILD(BranchNoHint, cond.node, &controls[0], &controls[1]);
    TFNode* merge = BUILD(Merge, 2, controls);
    TFNode* vals[2] = {tval.node, fval.node};
    TFNode* phi = BUILD(Phi, tval.type, 2, vals, merge);
    result->node = phi;
    ssa_env_->control = merge;
  }

  void Br(Decoder* decoder, Control* target) {
    MergeValuesInto(decoder, target, target->br_merge());
  }

  void BrIf(Decoder* decoder, const Value& cond, Control* target) {
    SsaEnv* fenv = ssa_env_;
    SsaEnv* tenv = Split(decoder, fenv);
    fenv->SetNotMerged();
    BUILD(BranchNoHint, cond.node, &tenv->control, &fenv->control);
    ssa_env_ = tenv;
    Br(decoder, target);
    ssa_env_ = fenv;
  }

  void BrTable(Decoder* decoder, const BranchTableOperand<validate>& operand,
               const Value& key) {
    if (operand.table_count == 0) {
      // Only a default target. Do the equivalent of br.
      uint32_t target = BranchTableIterator<validate>(decoder, operand).next();
      Br(decoder, decoder->control_at(target));
      return;
    }

    SsaEnv* break_env = ssa_env_;
    // Build branches to the various blocks based on the table.
    TFNode* sw = BUILD(Switch, operand.table_count + 1, key.node);

    SsaEnv* copy = Steal(decoder->zone(), break_env);
    ssa_env_ = copy;
    BranchTableIterator<validate> iterator(decoder, operand);
    while (iterator.has_next()) {
      uint32_t i = iterator.cur_index();
      uint32_t target = iterator.next();
      ssa_env_ = Split(decoder, copy);
      ssa_env_->control = (i == operand.table_count) ? BUILD(IfDefault, sw)
                                                     : BUILD(IfValue, i, sw);
      Br(decoder, decoder->control_at(target));
    }
    DCHECK(decoder->ok());
    ssa_env_ = break_env;
  }

  void Else(Decoder* decoder, Control* if_block) {
    SetEnv(if_block->false_env);
  }

  void LoadMem(Decoder* decoder, LoadType type,
               const MemoryAccessOperand<validate>& operand, const Value& index,
               Value* result) {
    result->node =
        BUILD(LoadMem, type.value_type(), type.mem_type(), index.node,
              operand.offset, operand.alignment, decoder->position());
  }

  void StoreMem(Decoder* decoder, StoreType type,
                const MemoryAccessOperand<validate>& operand,
                const Value& index, const Value& value) {
    BUILD(StoreMem, type.mem_rep(), index.node, operand.offset,
          operand.alignment, value.node, decoder->position(),
          type.value_type());
  }

  void CurrentMemoryPages(Decoder* decoder, Value* result) {
    result->node = BUILD(CurrentMemoryPages);
  }

  void GrowMemory(Decoder* decoder, const Value& value, Value* result) {
    result->node = BUILD(GrowMemory, value.node);
    // Always reload the context cache after growing memory.
    LoadContextIntoSsa(ssa_env_);
  }

  void CallDirect(Decoder* decoder,
                  const CallFunctionOperand<validate>& operand,
                  const Value args[], Value returns[]) {
    DoCall(decoder, nullptr, operand, args, returns, false);
  }

  void CallIndirect(Decoder* decoder, const Value& index,
                    const CallIndirectOperand<validate>& operand,
                    const Value args[], Value returns[]) {
    DoCall(decoder, index.node, operand, args, returns, true);
  }

  void SimdOp(Decoder* decoder, WasmOpcode opcode, Vector<Value> args,
              Value* result) {
    TFNode** inputs = GetNodes(args);
    TFNode* node = BUILD(SimdOp, opcode, inputs);
    if (result) result->node = node;
  }

  void SimdLaneOp(Decoder* decoder, WasmOpcode opcode,
                  const SimdLaneOperand<validate> operand, Vector<Value> inputs,
                  Value* result) {
    TFNode** nodes = GetNodes(inputs);
    result->node = BUILD(SimdLaneOp, opcode, operand.lane, nodes);
  }

  void SimdShiftOp(Decoder* decoder, WasmOpcode opcode,
                   const SimdShiftOperand<validate> operand, const Value& input,
                   Value* result) {
    TFNode* inputs[] = {input.node};
    result->node = BUILD(SimdShiftOp, opcode, operand.shift, inputs);
  }

  void Simd8x16ShuffleOp(Decoder* decoder,
                         const Simd8x16ShuffleOperand<validate>& operand,
                         const Value& input0, const Value& input1,
                         Value* result) {
    TFNode* input_nodes[] = {input0.node, input1.node};
    result->node = BUILD(Simd8x16ShuffleOp, operand.shuffle, input_nodes);
  }

  TFNode* GetExceptionTag(Decoder* decoder,
                          const ExceptionIndexOperand<validate>& operand) {
    // TODO(kschimpf): Need to get runtime exception tag values. This
    // code only handles non-imported/exported exceptions.
    return BUILD(Int32Constant, operand.index);
  }

  void Throw(Decoder* decoder, const ExceptionIndexOperand<validate>& operand,
             Control* block, const Vector<Value>& value_args) {
    int count = value_args.length();
    ZoneVector<TFNode*> args(count, decoder->zone());
    for (int i = 0; i < count; ++i) {
      args[i] = value_args[i].node;
    }
    BUILD(Throw, operand.index, operand.exception, vec2vec(args));
    Unreachable(decoder);
    EndControl(decoder, block);
  }

  void CatchException(Decoder* decoder,
                      const ExceptionIndexOperand<validate>& operand,
                      Control* block, Vector<Value> values) {
    DCHECK(block->is_try_catch());
    current_catch_ = block->previous_catch;
    SsaEnv* catch_env = block->try_info->catch_env;
    SetEnv(catch_env);

    TFNode* compare_i32 = nullptr;
    if (block->try_info->exception == nullptr) {
      // Catch not applicable, no possible throws in the try
      // block. Create dummy code so that body of catch still
      // compiles. Note: This only happens because the current
      // implementation only builds a landing pad if some node in the
      // try block can (possibly) throw.
      //
      // TODO(kschimpf): Always generate a landing pad for a try block.
      compare_i32 = BUILD(Int32Constant, 0);
    } else {
      // Get the exception and see if wanted exception.
      TFNode* caught_tag = BUILD(GetExceptionRuntimeId);
      TFNode* exception_tag =
          BUILD(ConvertExceptionTagToRuntimeId, operand.index);
      compare_i32 = BUILD(Binop, kExprI32Eq, caught_tag, exception_tag);
    }

    TFNode* if_catch = nullptr;
    TFNode* if_no_catch = nullptr;
    BUILD(BranchNoHint, compare_i32, &if_catch, &if_no_catch);

    SsaEnv* if_no_catch_env = Split(decoder, ssa_env_);
    if_no_catch_env->control = if_no_catch;
    SsaEnv* if_catch_env = Steal(decoder->zone(), ssa_env_);
    if_catch_env->control = if_catch;

    // TODO(kschimpf): Generalize to allow more catches. Will force
    // moving no_catch code to END opcode.
    SetEnv(if_no_catch_env);
    BUILD(Rethrow);
    Unreachable(decoder);
    EndControl(decoder, block);

    SetEnv(if_catch_env);

    if (block->try_info->exception == nullptr) {
      // No caught value, make up filler nodes so that catch block still
      // compiles.
      for (Value& value : values) {
        value.node = DefaultValue(value.type);
      }
    } else {
      // TODO(kschimpf): Can't use BUILD() here, GetExceptionValues() returns
      // TFNode** rather than TFNode*. Fix to add landing pads.
      TFNode** caught_values = builder_->GetExceptionValues(operand.exception);
      for (size_t i = 0, e = values.size(); i < e; ++i) {
        values[i].node = caught_values[i];
      }
    }
  }

  void AtomicOp(Decoder* decoder, WasmOpcode opcode, Vector<Value> args,
                const MemoryAccessOperand<validate>& operand, Value* result) {
    TFNode** inputs = GetNodes(args);
    TFNode* node = BUILD(AtomicOp, opcode, inputs, operand.alignment,
                         operand.offset, decoder->position());
    if (result) result->node = node;
  }

 private:
  SsaEnv* ssa_env_;
  TFBuilder* builder_;
  uint32_t current_catch_ = kNullCatch;

  TryInfo* current_try_info(Decoder* decoder) {
    return decoder->control_at(decoder->control_depth() - 1 - current_catch_)
        ->try_info;
  }

  TFNode** GetNodes(Value* values, size_t count) {
    TFNode** nodes = builder_->Buffer(count);
    for (size_t i = 0; i < count; ++i) {
      nodes[i] = values[i].node;
    }
    return nodes;
  }

  TFNode** GetNodes(Vector<Value> values) {
    return GetNodes(values.start(), values.size());
  }

  void SetEnv(SsaEnv* env) {
#if DEBUG
    if (FLAG_trace_wasm_decoder) {
      char state = 'X';
      if (env) {
        switch (env->state) {
          case SsaEnv::kReached:
            state = 'R';
            break;
          case SsaEnv::kUnreachable:
            state = 'U';
            break;
          case SsaEnv::kMerged:
            state = 'M';
            break;
          case SsaEnv::kControlEnd:
            state = 'E';
            break;
        }
      }
      PrintF("{set_env = %p, state = %c", static_cast<void*>(env), state);
      if (env && env->control) {
        PrintF(", control = ");
        compiler::WasmGraphBuilder::PrintDebugName(env->control);
      }
      PrintF("}\n");
    }
#endif
    ssa_env_ = env;
    // TODO(wasm): combine the control and effect pointers with context cache.
    builder_->set_control_ptr(&env->control);
    builder_->set_effect_ptr(&env->effect);
    builder_->set_context_cache(&env->context_cache);
  }

  TFNode* CheckForException(Decoder* decoder, TFNode* node) {
    if (node == nullptr) return nullptr;

    const bool inside_try_scope = current_catch_ != kNullCatch;

    if (!inside_try_scope) return node;

    TFNode* if_success = nullptr;
    TFNode* if_exception = nullptr;
    if (!builder_->ThrowsException(node, &if_success, &if_exception)) {
      return node;
    }

    SsaEnv* success_env = Steal(decoder->zone(), ssa_env_);
    success_env->control = if_success;

    SsaEnv* exception_env = Split(decoder, success_env);
    exception_env->control = if_exception;
    TryInfo* try_info = current_try_info(decoder);
    Goto(decoder, exception_env, try_info->catch_env);
    TFNode* exception = try_info->exception;
    if (exception == nullptr) {
      DCHECK_EQ(SsaEnv::kReached, try_info->catch_env->state);
      try_info->exception = if_exception;
    } else {
      DCHECK_EQ(SsaEnv::kMerged, try_info->catch_env->state);
      try_info->exception =
          builder_->CreateOrMergeIntoPhi(kWasmI32, try_info->catch_env->control,
                                         try_info->exception, if_exception);
    }

    SetEnv(success_env);
    return node;
  }

  TFNode* DefaultValue(ValueType type) {
    switch (type) {
      case kWasmI32:
        return builder_->Int32Constant(0);
      case kWasmI64:
        return builder_->Int64Constant(0);
      case kWasmF32:
        return builder_->Float32Constant(0);
      case kWasmF64:
        return builder_->Float64Constant(0);
      case kWasmS128:
        return builder_->S128Zero();
      default:
        UNREACHABLE();
    }
  }

  void MergeValuesInto(Decoder* decoder, Control* c, Merge<Value>* merge) {
    DCHECK(merge == &c->start_merge || merge == &c->end_merge);
    if (!ssa_env_->go()) return;

    SsaEnv* target = c->end_env;
    const bool first = target->state == SsaEnv::kUnreachable;
    Goto(decoder, ssa_env_, target);

    uint32_t avail =
        decoder->stack_size() - decoder->control_at(0)->stack_depth;
    uint32_t start = avail >= merge->arity ? 0 : merge->arity - avail;
    for (uint32_t i = start; i < merge->arity; ++i) {
      auto& val = decoder->GetMergeValueFromStack(c, merge, i);
      auto& old = (*merge)[i];
      DCHECK_NOT_NULL(val.node);
      DCHECK(val.type == old.type || val.type == kWasmVar);
      old.node = first ? val.node
                       : builder_->CreateOrMergeIntoPhi(
                             old.type, target->control, old.node, val.node);
    }
  }

  void Goto(Decoder* decoder, SsaEnv* from, SsaEnv* to) {
    DCHECK_NOT_NULL(to);
    if (!from->go()) return;
    switch (to->state) {
      case SsaEnv::kUnreachable: {  // Overwrite destination.
        to->state = SsaEnv::kReached;
        to->locals = from->locals;
        to->control = from->control;
        to->effect = from->effect;
        to->context_cache = from->context_cache;
        break;
      }
      case SsaEnv::kReached: {  // Create a new merge.
        to->state = SsaEnv::kMerged;
        // Merge control.
        TFNode* controls[] = {to->control, from->control};
        TFNode* merge = builder_->Merge(2, controls);
        to->control = merge;
        // Merge effects.
        if (from->effect != to->effect) {
          TFNode* effects[] = {to->effect, from->effect, merge};
          to->effect = builder_->EffectPhi(2, effects, merge);
        }
        // Merge SSA values.
        for (int i = decoder->NumLocals() - 1; i >= 0; i--) {
          TFNode* a = to->locals[i];
          TFNode* b = from->locals[i];
          if (a != b) {
            TFNode* vals[] = {a, b};
            to->locals[i] =
                builder_->Phi(decoder->GetLocalType(i), 2, vals, merge);
          }
        }
        // Start a new merge from the context cache.
        builder_->NewContextCacheMerge(&to->context_cache, &from->context_cache,
                                       merge);
        break;
      }
      case SsaEnv::kMerged: {
        TFNode* merge = to->control;
        // Extend the existing merge control node.
        builder_->AppendToMerge(merge, from->control);
        // Merge effects.
        to->effect = builder_->CreateOrMergeIntoEffectPhi(merge, to->effect,
                                                          from->effect);
        // Merge locals.
        for (int i = decoder->NumLocals() - 1; i >= 0; i--) {
          to->locals[i] = builder_->CreateOrMergeIntoPhi(
              decoder->GetLocalType(i), merge, to->locals[i], from->locals[i]);
        }
        // Merge the context caches.
        builder_->MergeContextCacheInto(&to->context_cache,
                                        &from->context_cache, merge);
        break;
      }
      default:
        UNREACHABLE();
    }
    return from->Kill();
  }

  SsaEnv* PrepareForLoop(Decoder* decoder, SsaEnv* env) {
    if (!env->go()) return Split(decoder, env);
    env->state = SsaEnv::kMerged;

    env->control = builder_->Loop(env->control);
    env->effect = builder_->EffectPhi(1, &env->effect, env->control);
    builder_->Terminate(env->effect, env->control);
    // The '+ 1' here is to be able to set the context cache as assigned.
    BitVector* assigned = WasmDecoder<validate>::AnalyzeLoopAssignment(
        decoder, decoder->pc(), decoder->total_locals() + 1, decoder->zone());
    if (decoder->failed()) return env;
    if (assigned != nullptr) {
      // Only introduce phis for variables assigned in this loop.
      int context_cache_index = decoder->total_locals();
      for (int i = decoder->NumLocals() - 1; i >= 0; i--) {
        if (!assigned->Contains(i)) continue;
        env->locals[i] = builder_->Phi(decoder->GetLocalType(i), 1,
                                       &env->locals[i], env->control);
      }
      // Introduce phis for context cache pointers if necessary.
      if (assigned->Contains(context_cache_index)) {
        builder_->PrepareContextCacheForLoop(&env->context_cache, env->control);
      }

      SsaEnv* loop_body_env = Split(decoder, env);
      builder_->StackCheck(decoder->position(), &(loop_body_env->effect),
                           &(loop_body_env->control));
      return loop_body_env;
    }

    // Conservatively introduce phis for all local variables.
    for (int i = decoder->NumLocals() - 1; i >= 0; i--) {
      env->locals[i] = builder_->Phi(decoder->GetLocalType(i), 1,
                                     &env->locals[i], env->control);
    }

    // Conservatively introduce phis for context cache.
    builder_->PrepareContextCacheForLoop(&env->context_cache, env->control);

    SsaEnv* loop_body_env = Split(decoder, env);
    builder_->StackCheck(decoder->position(), &loop_body_env->effect,
                         &loop_body_env->control);
    return loop_body_env;
  }

  // Create a complete copy of {from}.
  SsaEnv* Split(Decoder* decoder, SsaEnv* from) {
    DCHECK_NOT_NULL(from);
    SsaEnv* result =
        reinterpret_cast<SsaEnv*>(decoder->zone()->New(sizeof(SsaEnv)));
    size_t size = sizeof(TFNode*) * decoder->NumLocals();
    result->control = from->control;
    result->effect = from->effect;

    if (from->go()) {
      result->state = SsaEnv::kReached;
      result->locals =
          size > 0 ? reinterpret_cast<TFNode**>(decoder->zone()->New(size))
                   : nullptr;
      memcpy(result->locals, from->locals, size);
      result->context_cache = from->context_cache;
    } else {
      result->state = SsaEnv::kUnreachable;
      result->locals = nullptr;
      result->context_cache = {0};
    }

    return result;
  }

  // Create a copy of {from} that steals its state and leaves {from}
  // unreachable.
  SsaEnv* Steal(Zone* zone, SsaEnv* from) {
    DCHECK_NOT_NULL(from);
    if (!from->go()) return UnreachableEnv(zone);
    SsaEnv* result = reinterpret_cast<SsaEnv*>(zone->New(sizeof(SsaEnv)));
    result->state = SsaEnv::kReached;
    result->locals = from->locals;
    result->control = from->control;
    result->effect = from->effect;
    result->context_cache = from->context_cache;
    from->Kill(SsaEnv::kUnreachable);
    return result;
  }

  // Create an unreachable environment.
  SsaEnv* UnreachableEnv(Zone* zone) {
    SsaEnv* result = reinterpret_cast<SsaEnv*>(zone->New(sizeof(SsaEnv)));
    result->state = SsaEnv::kUnreachable;
    result->control = nullptr;
    result->effect = nullptr;
    result->locals = nullptr;
    result->context_cache = {0};
    return result;
  }

  template <typename Operand>
  void DoCall(WasmFullDecoder<validate, WasmGraphBuildingInterface>* decoder,
              TFNode* index_node, const Operand& operand, const Value args[],
              Value returns[], bool is_indirect) {
    int param_count = static_cast<int>(operand.sig->parameter_count());
    TFNode** arg_nodes = builder_->Buffer(param_count + 1);
    TFNode** return_nodes = nullptr;
    arg_nodes[0] = index_node;
    for (int i = 0; i < param_count; ++i) {
      arg_nodes[i + 1] = args[i].node;
    }
    if (is_indirect) {
      builder_->CallIndirect(operand.index, arg_nodes, &return_nodes,
                             decoder->position());
    } else {
      builder_->CallDirect(operand.index, arg_nodes, &return_nodes,
                           decoder->position());
    }
    int return_count = static_cast<int>(operand.sig->return_count());
    for (int i = 0; i < return_count; ++i) {
      returns[i].node = return_nodes[i];
    }
    // The invoked function could have used grow_memory, so we need to
    // reload mem_size and mem_start
    LoadContextIntoSsa(ssa_env_);
  }
};

}  // namespace

bool DecodeLocalDecls(BodyLocalDecls* decls, const byte* start,
                      const byte* end) {
  Decoder decoder(start, end);
  if (WasmDecoder<Decoder::kValidate>::DecodeLocals(&decoder, nullptr,
                                                    &decls->type_list)) {
    DCHECK(decoder.ok());
    decls->encoded_size = decoder.pc_offset();
    return true;
  }
  return false;
}

BytecodeIterator::BytecodeIterator(const byte* start, const byte* end,
                                   BodyLocalDecls* decls)
    : Decoder(start, end) {
  if (decls != nullptr) {
    if (DecodeLocalDecls(decls, start, end)) {
      pc_ += decls->encoded_size;
      if (pc_ > end_) pc_ = end_;
    }
  }
}

DecodeResult VerifyWasmCode(AccountingAllocator* allocator,
                            const wasm::WasmModule* module,
                            FunctionBody& body) {
  Zone zone(allocator, ZONE_NAME);
  WasmFullDecoder<Decoder::kValidate, EmptyInterface> decoder(&zone, module,
                                                              body);
  decoder.Decode();
  return decoder.toResult(nullptr);
}

DecodeResult VerifyWasmCodeWithStats(AccountingAllocator* allocator,
                                     const wasm::WasmModule* module,
                                     FunctionBody& body, bool is_wasm,
                                     Counters* counters) {
  CHECK_LE(0, body.end - body.start);
  auto time_counter = is_wasm ? counters->wasm_decode_wasm_function_time()
                              : counters->wasm_decode_asm_function_time();
  TimedHistogramScope wasm_decode_function_time_scope(time_counter);
  return VerifyWasmCode(allocator, module, body);
}

DecodeResult BuildTFGraph(AccountingAllocator* allocator, TFBuilder* builder,
                          FunctionBody& body) {
  Zone zone(allocator, ZONE_NAME);
  WasmFullDecoder<Decoder::kValidate, WasmGraphBuildingInterface> decoder(
      &zone, builder->module(), body, builder);
  decoder.Decode();
  return decoder.toResult(nullptr);
}

unsigned OpcodeLength(const byte* pc, const byte* end) {
  Decoder decoder(pc, end);
  return WasmDecoder<Decoder::kNoValidate>::OpcodeLength(&decoder, pc);
}

std::pair<uint32_t, uint32_t> StackEffect(const WasmModule* module,
                                          FunctionSig* sig, const byte* pc,
                                          const byte* end) {
  WasmDecoder<Decoder::kNoValidate> decoder(module, sig, pc, end);
  return decoder.StackEffect(pc);
}

void PrintRawWasmCode(const byte* start, const byte* end) {
  AccountingAllocator allocator;
  PrintRawWasmCode(&allocator, FunctionBody{nullptr, 0, start, end}, nullptr,
                   kPrintLocals);
}

namespace {
const char* RawOpcodeName(WasmOpcode opcode) {
  switch (opcode) {
#define DECLARE_NAME_CASE(name, opcode, sig) \
  case kExpr##name:                          \
    return "kExpr" #name;
    FOREACH_OPCODE(DECLARE_NAME_CASE)
#undef DECLARE_NAME_CASE
    default:
      break;
  }
  return "Unknown";
}
}  // namespace

bool PrintRawWasmCode(AccountingAllocator* allocator, const FunctionBody& body,
                      const wasm::WasmModule* module,
                      PrintLocals print_locals) {
  OFStream os(stdout);
  Zone zone(allocator, ZONE_NAME);
  WasmDecoder<Decoder::kNoValidate> decoder(module, body.sig, body.start,
                                            body.end);
  int line_nr = 0;

  // Print the function signature.
  if (body.sig) {
    os << "// signature: " << *body.sig << std::endl;
    ++line_nr;
  }

  // Print the local declarations.
  BodyLocalDecls decls(&zone);
  BytecodeIterator i(body.start, body.end, &decls);
  if (body.start != i.pc() && print_locals == kPrintLocals) {
    os << "// locals: ";
    if (!decls.type_list.empty()) {
      ValueType type = decls.type_list[0];
      uint32_t count = 0;
      for (size_t pos = 0; pos < decls.type_list.size(); ++pos) {
        if (decls.type_list[pos] == type) {
          ++count;
        } else {
          os << " " << count << " " << WasmOpcodes::TypeName(type);
          type = decls.type_list[pos];
          count = 1;
        }
      }
    }
    os << std::endl;
    ++line_nr;

    for (const byte* locals = body.start; locals < i.pc(); locals++) {
      os << (locals == body.start ? "0x" : " 0x") << AsHex(*locals, 2) << ",";
    }
    os << std::endl;
    ++line_nr;
  }

  os << "// body: " << std::endl;
  ++line_nr;
  unsigned control_depth = 0;
  for (; i.has_next(); i.next()) {
    unsigned length =
        WasmDecoder<Decoder::kNoValidate>::OpcodeLength(&decoder, i.pc());

    WasmOpcode opcode = i.current();
    if (opcode == kExprElse) control_depth--;

    int num_whitespaces = control_depth < 32 ? 2 * control_depth : 64;

    // 64 whitespaces
    const char* padding =
        "                                                                ";
    os.write(padding, num_whitespaces);

    os << RawOpcodeName(opcode) << ",";

    for (unsigned j = 1; j < length; ++j) {
      os << " 0x" << AsHex(i.pc()[j], 2) << ",";
    }

    switch (opcode) {
      case kExprElse:
        os << "   // @" << i.pc_offset();
        control_depth++;
        break;
      case kExprLoop:
      case kExprIf:
      case kExprBlock:
      case kExprTry: {
        BlockTypeOperand<Decoder::kNoValidate> operand(&i, i.pc());
        os << "   // @" << i.pc_offset();
        for (unsigned i = 0; i < operand.out_arity(); i++) {
          os << " " << WasmOpcodes::TypeName(operand.out_type(i));
        }
        control_depth++;
        break;
      }
      case kExprEnd:
        os << "   // @" << i.pc_offset();
        control_depth--;
        break;
      case kExprBr: {
        BreakDepthOperand<Decoder::kNoValidate> operand(&i, i.pc());
        os << "   // depth=" << operand.depth;
        break;
      }
      case kExprBrIf: {
        BreakDepthOperand<Decoder::kNoValidate> operand(&i, i.pc());
        os << "   // depth=" << operand.depth;
        break;
      }
      case kExprBrTable: {
        BranchTableOperand<Decoder::kNoValidate> operand(&i, i.pc());
        os << " // entries=" << operand.table_count;
        break;
      }
      case kExprCallIndirect: {
        CallIndirectOperand<Decoder::kNoValidate> operand(&i, i.pc());
        os << "   // sig #" << operand.index;
        if (decoder.Complete(i.pc(), operand)) {
          os << ": " << *operand.sig;
        }
        break;
      }
      case kExprCallFunction: {
        CallFunctionOperand<Decoder::kNoValidate> operand(&i, i.pc());
        os << " // function #" << operand.index;
        if (decoder.Complete(i.pc(), operand)) {
          os << ": " << *operand.sig;
        }
        break;
      }
      default:
        break;
    }
    os << std::endl;
    ++line_nr;
  }

  return decoder.ok();
}

BitVector* AnalyzeLoopAssignmentForTesting(Zone* zone, size_t num_locals,
                                           const byte* start, const byte* end) {
  Decoder decoder(start, end);
  return WasmDecoder<Decoder::kValidate>::AnalyzeLoopAssignment(
      &decoder, start, static_cast<uint32_t>(num_locals), zone);
}

#undef BUILD

}  // namespace wasm
}  // namespace internal
}  // namespace v8