[WASM] Exception handling prototype.

src/wasm/ast-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/bit-vector.h"
 #include "src/flags.h"
 #include "src/handles.h"
 #include "src/zone-containers.h"
@@ skipping 50 matching lines @@
   TFNode* node;
   LocalType type;
 };
 
 // An entry on the control stack (i.e. if, block, loop).
 struct Control {
   const byte* pc;
   int stack_depth;    // stack height at the beginning of the construct.
   SsaEnv* end_env;    // end environment for the construct.
   SsaEnv* false_env;  // false environment (only for if).
+  SsaEnv* catch_env;  // catch environment (only for try with catch).
+  SsaEnv* cont_env;   // continuation environment (only for try with finally).

[bradnelson, 2016/08/11 00:39:29]

This name is confusing, implies continue as in the statement / loops, and
happens to match a local down in Loop.
How about finish_try_env, or if you can think of better?

[John, 2016/08/11 11:22:27]

Yeah, cont_env threw me off a few times, but I couldn't come up with anything
better. Going with finish_try_env.

   TFNode* node;       // result node for the construct.
   LocalType type;     // result type for the construct.
   bool is_loop;       // true if this is the inner label of a loop.
 
-  bool is_if() { return *pc == kExprIf; }
-  bool is_block() { return *pc == kExprBlock; }
+  bool is_if() const { return *pc == kExprIf; }
+
+  bool is_try() const {
+    return *pc == kExprTryCatch || *pc == kExprTryCatchFinally ||
+           *pc == kExprTryFinally;
+  }
+
+  bool has_catch() const {
+    return *pc == kExprTryCatch || *pc == kExprTryCatchFinally;
+  }
+
+  bool has_finally() const {
+    return *pc == kExprTryCatchFinally || *pc == kExprTryFinally;
+  }
+
+  // Named constructors.
+  static Control Block(const byte* pc, int stack_depth, SsaEnv* end_env) {
+    return {pc,      stack_depth, end_env, nullptr, nullptr,
+            nullptr, nullptr,     kAstEnd, false};
+  }
+
+  static Control If(const byte* pc, int stack_depth, SsaEnv* end_env,
+                    SsaEnv* false_env) {
+    return {pc,      stack_depth, end_env,  false_env, nullptr,
+            nullptr, nullptr,     kAstStmt, false};
+  }
+
+  static Control Loop(const byte* pc, int stack_depth, SsaEnv* end_env) {
+    return {pc,      stack_depth, end_env, nullptr, nullptr,
+            nullptr, nullptr,     kAstEnd, true};
+  }
+
+  static Control Try(const byte* pc, int stack_depth, SsaEnv* end_env,
+                     SsaEnv* catch_env, SsaEnv* cont_env) {
+    return {pc,       stack_depth, end_env, nullptr, catch_env,
+            cont_env, nullptr,     kAstEnd, false};
+  }
 };
 
 // Macros that build nodes only if there is a graph and the current SSA
 // environment is reachable from start. This avoids problems with malformed
 // TF graphs when decoding inputs that have unreachable code.
 #define BUILD(func, ...) (build() ? builder_->func(__VA_ARGS__) : nullptr)
 #define BUILD0(func) (build() ? builder_->func() : nullptr)
 
 // Generic Wasm bytecode decoder with utilities for decoding operands,
 // lengths, etc.
@@ skipping 150 matching lines @@
       case kExprI32Const:
       case kExprI64Const:
       case kExprF64Const:
       case kExprF32Const:
       case kExprGetLocal:
       case kExprGetGlobal:
       case kExprNop:
       case kExprUnreachable:
       case kExprEnd:
       case kExprBlock:
+      case kExprThrow:
+      case kExprTryCatch:
+      case kExprTryCatchFinally:
+      case kExprTryFinally:
+      case kExprFinally:
       case kExprLoop:
         return 0;
 
       case kExprSetGlobal:
       case kExprSetLocal:
       case kExprElse:
+      case kExprCatch:
         return 1;
 
       case kExprBr: {
         BreakDepthOperand operand(this, pc);
         return operand.arity;
       }
       case kExprBrIf: {
         BreakDepthOperand operand(this, pc);
         return 1 + operand.arity;
       }
@@ skipping 70 matching lines @@
       case kExprCallIndirect: {
         CallIndirectOperand operand(this, pc);
         return 1 + operand.length;
       }
       case kExprCallImport: {
         CallImportOperand operand(this, pc);
         return 1 + operand.length;
       }
 
       case kExprSetLocal:
-      case kExprGetLocal: {
+      case kExprGetLocal:
+      case kExprCatch: {
         LocalIndexOperand operand(this, pc);
         return 1 + operand.length;
       }
       case kExprBrTable: {
         BranchTableOperand operand(this, pc);
         return 1 + operand.length;
       }
       case kExprI32Const: {
         ImmI32Operand operand(this, pc);
         return 1 + operand.length;
@@ skipping 265 matching lines @@
           case kExprNop:
             Push(kAstStmt, nullptr);
             break;
           case kExprBlock: {
             // The break environment is the outer environment.
             SsaEnv* break_env = ssa_env_;
             PushBlock(break_env);
             SetEnv("block:start", Steal(break_env));
             break;
           }
+          case kExprThrow: {
+            if (!FLAG_wasm_eh_prototype) {
+              error("Invalid opcode");
+              return;
+            }
+
+            // TODO(jpp): validate the poped value.
+            Pop();
+
+            // TODO(jpp): start exception propagation.
+            break;
+          }
+          case kExprTryCatch: {
+            if (!FLAG_wasm_eh_prototype) {
+              error("Invalid opcode");
+              return;
+            }
+
+            SsaEnv* outer_env = ssa_env_;
+            SsaEnv* try_env = Steal(outer_env);
+            SsaEnv* catch_env = Split(try_env);
+            PushTry(outer_env, catch_env, nullptr);
+            SetEnv("try_catch:start", try_env);
+            break;
+          }
+          case kExprTryCatchFinally: {
+            if (!FLAG_wasm_eh_prototype) {
+              error("Invalid opcode");
+              return;
+            }
+
+            SsaEnv* outer_env = ssa_env_;
+            SsaEnv* try_env = Steal(outer_env);
+            SsaEnv* catch_env = Split(try_env);
+            SsaEnv* finally_env = Split(try_env);
+            PushTry(finally_env, catch_env, outer_env);
+            SetEnv("try_catch_finally:start", try_env);
+            break;
+          }
+          case kExprTryFinally: {
+            if (!FLAG_wasm_eh_prototype) {
+              error("Invalid opcode");
+              return;
+            }
+
+            SsaEnv* outer_env = ssa_env_;
+            SsaEnv* try_env = Steal(outer_env);
+            SsaEnv* finally_env = Split(outer_env);
+            PushTry(finally_env, nullptr, outer_env);
+            SetEnv("try_finally:start", try_env);
+            break;
+          }
+          case kExprCatch: {
+            if (!FLAG_wasm_eh_prototype) {
+              error("Invalid opcode");
+              return;
+            }
+
+            LocalIndexOperand operand(this, pc_);
+            len = 1 + operand.length;
+
+            if (control_.empty()) {
+              error(pc_, "catch does not match a any try");
+              break;
+            }
+
+            Control* c = &control_.back();
+            if (!c->has_catch()) {
+              error(pc_, "catch does not match a try with catch");
+              break;
+            }
+
+            if (c->catch_env == nullptr) {
+              error(pc_, "catch already present for try with catch");
+              break;
+            }
+
+            Goto(ssa_env_, c->end_env);
+
+            SsaEnv* catch_env = c->catch_env;
+            c->catch_env = nullptr;
+            SetEnv("catch:begin", catch_env);
+
+            if (Validate(pc_, operand)) {
+              // TODO(jpp): figure out how thrown value is propagated. It is
+              // unlikely to be a value on the stack.
+              if (ssa_env_->locals) {
+                ssa_env_->locals[operand.index] = nullptr;
+              }
+            }
+
+            PopUpTo(c->stack_depth);
+
+            break;
+          }
+          case kExprFinally: {
+            if (!FLAG_wasm_eh_prototype) {
+              error("Invalid opcode");
+              return;
+            }
+
+            if (control_.empty()) {
+              error(pc_, "finally does not match a any try");
+              break;
+            }
+
+            Control* c = &control_.back();
+            if (c->has_catch() && c->catch_env != nullptr) {
+              error(pc_, "missing catch for try with catch and finally");
+              break;
+            }
+
+            if (!c->has_finally()) {
+              error(pc_, "finally does not match a try with finally");
+              break;
+            }
+
+            if (c->cont_env == nullptr) {
+              error(pc_, "finally already present for try with finally");
+              break;
+            }
+
+            // ssa_env_ is either the env for either the try or the catch, but
+            // it does not matter: either way we need to direct the control flow
+            // to the end_env, which is the env for the finally. c->cont_env is
+            // the "continuation" environment - essentially, the environment
+            // where the try block appeared.
+            Goto(ssa_env_, c->end_env);
+
+            PopUpTo(c->stack_depth);
+
+            // The current environment becomes end_env, and cont_env becomes the
+            // new end_env. This ensures that any control flow leaving a try
+            // block up to now will do so by branching to the finally block.
+            // Setting the end_env to be cont_env ensures that kExprEnd below
+            // can handle the try block as it would any other block construct.
+            SsaEnv* finally_env = c->end_env;
+            c->end_env = c->cont_env;
+            SetEnv("finally:begin", finally_env);
+            c->cont_env = nullptr;
+
+            break;
+          }
           case kExprLoop: {
             // The break environment is the outer environment.
             SsaEnv* break_env = ssa_env_;
             PushBlock(break_env);
             SsaEnv* cont_env = Steal(break_env);
             // The continue environment is the inner environment.
             PrepareForLoop(pc_, cont_env);
             SetEnv("loop:start", Split(cont_env));
             ssa_env_->SetNotMerged();
             PushLoop(cont_env);
@@ skipping 35 matching lines @@
             c->false_env = nullptr;  // record that an else is already seen
             break;
           }
           case kExprEnd: {
             if (control_.empty()) {
               error(pc_, "end does not match any if or block");
               break;
             }
             const char* name = "block:end";
             Control* c = &control_.back();
+            Value val = PopUpTo(c->stack_depth);
             if (c->is_loop) {
               // Loops always push control in pairs.
               control_.pop_back();
               c = &control_.back();
               name = "loop:end";
-            }
-            Value val = PopUpTo(c->stack_depth);
-            if (c->is_if()) {
+            } else if (c->is_if()) {
               if (c->false_env != nullptr) {
                 // End the true branch of a one-armed if.
                 Goto(c->false_env, c->end_env);
                 val = {val.pc, nullptr, kAstStmt};
                 name = "if:merge";
               } else {
                 // End the false branch of a two-armed if.
                 name = "if_else:merge";
               }
+            } else if (c->is_try()) {
+              DCHECK(FLAG_wasm_eh_prototype);
+
+              name = "try:end";
+
+              // try blocks do not yield a value.
+              val = {val.pc, nullptr, kAstStmt};
+
+              // validate that catch/finally were seen.
+              if (c->catch_env != nullptr) {
+                error(pc_, "missing catch in try with catch");
+                break;
+              }
+
+              if (c->cont_env != nullptr) {
+                error(pc_, "missing finally in try with finally");
+                break;
+              }
             }
+
             if (ssa_env_->go()) {
               MergeInto(c->end_env, &c->node, &c->type, val);
             }
             SetEnv(name, c->end_env);
             stack_.resize(c->stack_depth);
             Push(c->type, c->node);
             control_.pop_back();
             break;
           }
           case kExprSelect: {
@@ skipping 277 matching lines @@
             if (Validate(pc_, operand)) {
               TFNode** buffer = PopArgs(operand.sig);
               TFNode* call =
                   BUILD(CallImport, operand.index, buffer, position());
               Push(GetReturnType(operand.sig), call);
             }
             len = 1 + operand.length;
             break;
           }
           case kSimdPrefix: {
-            if (FLAG_wasm_simd_prototype) {
-              len++;
-              byte simd_index = *(pc_ + 1);
-              opcode = static_cast<WasmOpcode>(opcode << 8 | simd_index);
-              DecodeSimdOpcode(opcode);
-              break;
+            if (!FLAG_wasm_simd_prototype) {
+              error("Invalid opcode");
+              return;
             }
+            len++;
+            byte simd_index = *(pc_ + 1);
+            opcode = static_cast<WasmOpcode>(opcode << 8 | simd_index);
+            DecodeSimdOpcode(opcode);
+            break;
           }
           default:
             error("Invalid opcode");
             return;
         }
       }  // end complex bytecode
 
 #if DEBUG
       if (FLAG_trace_wasm_decoder) {
         for (size_t i = 0; i < stack_.size(); ++i) {
@@ skipping 50 matching lines @@
       }
       return nullptr;
     }
   }
 
   LocalType GetReturnType(FunctionSig* sig) {
     return sig->return_count() == 0 ? kAstStmt : sig->GetReturn();
   }
 
   void PushBlock(SsaEnv* end_env) {
-    int stack_depth = static_cast<int>(stack_.size());
-    control_.push_back(
-        {pc_, stack_depth, end_env, nullptr, nullptr, kAstEnd, false});
+    const int stack_depth = static_cast<int>(stack_.size());
+    control_.emplace_back(Control::Block(pc_, stack_depth, end_env));
   }
 
   void PushLoop(SsaEnv* end_env) {
-    int stack_depth = static_cast<int>(stack_.size());
-    control_.push_back(
-        {pc_, stack_depth, end_env, nullptr, nullptr, kAstEnd, true});
+    const int stack_depth = static_cast<int>(stack_.size());
+    control_.emplace_back(Control::Loop(pc_, stack_depth, end_env));
   }
 
   void PushIf(SsaEnv* end_env, SsaEnv* false_env) {
-    int stack_depth = static_cast<int>(stack_.size());
-    control_.push_back(
-        {pc_, stack_depth, end_env, false_env, nullptr, kAstStmt, false});
+    const int stack_depth = static_cast<int>(stack_.size());
+    control_.emplace_back(Control::If(pc_, stack_depth, end_env, false_env));
+  }
+
+  void PushTry(SsaEnv* end_env, SsaEnv* catch_env, SsaEnv* cont_env) {
+    const int stack_depth = static_cast<int>(stack_.size());
+    control_.emplace_back(
+        Control::Try(pc_, stack_depth, end_env, catch_env, cont_env));
   }
 
   int DecodeLoadMem(LocalType type, MachineType mem_type) {
     MemoryAccessOperand operand(this, pc_);
     Value index = Pop(0, kAstI32);
     TFNode* node = BUILD(LoadMem, type, mem_type, index.node, operand.offset,
                          operand.alignment, position());
     Push(type, node);
     return 1 + operand.length;
   }
@@ skipping 333 matching lines @@
         new (zone_) BitVector(static_cast<int>(local_type_vec_.size()), zone_);
     int depth = 0;
     // Iteratively process all AST nodes nested inside the loop.
     while (pc < limit_ && ok()) {
       WasmOpcode opcode = static_cast<WasmOpcode>(*pc);
       unsigned length = 1;
       switch (opcode) {
         case kExprLoop:
         case kExprIf:
         case kExprBlock:
+        case kExprTryCatch:
+        case kExprTryCatchFinally:
+        case kExprTryFinally:
           depth++;
           DCHECK_EQ(1, OpcodeLength(pc));
           break;
         case kExprSetLocal: {
           LocalIndexOperand operand(this, pc);
           if (assigned->length() > 0 &&
               static_cast<int>(operand.index) < assigned->length()) {
             // Unverified code might have an out-of-bounds index.
             assigned->Add(operand.index);
           }
@@ skipping 128 matching lines @@
 
     for (size_t j = 1; j < length; ++j) {
       os << " " << AsHex(i.pc()[j], 2) << ",";
     }
 
     switch (opcode) {
       case kExprIf:
       case kExprElse:
       case kExprLoop:
       case kExprBlock:
+      case kExprTryCatch:
+      case kExprTryCatchFinally:
+      case kExprTryFinally:
         os << "   // @" << i.pc_offset();
         control_depth++;
         break;
       case kExprEnd:
         os << "   // @" << i.pc_offset();
         control_depth--;
         break;
       case kExprBr: {
         BreakDepthOperand operand(&i, i.pc());
         os << "   // arity=" << operand.arity << " depth=" << operand.depth;
@@ skipping 55 matching lines @@
 BitVector* AnalyzeLoopAssignmentForTesting(Zone* zone, size_t num_locals,
                                            const byte* start, const byte* end) {
   FunctionBody body = {nullptr, nullptr, nullptr, start, end};
   WasmFullDecoder decoder(zone, nullptr, body);
   return decoder.AnalyzeLoopAssignmentForTesting(start, num_locals);
 }
 
 }  // namespace wasm
 }  // namespace internal
 }  // namespace v8