[WASM] Exception handling prototype.

------------------------------------------------------------------------

This CL adds support for decoding eh-related wasm opcodes:
* Throw: used for raising an exception; the thrown value lives on top of
         the evaluation stack;
* TryCatch: used to start a try block that has a catch clause;
* TryFinally: used to start a try block that has a finally clause;
* TryCatchFinally: used to start a try block that has both catch and
                   finally clauses;
* Catch <local>: used to start the catch block of a
                 TryCatch/TryCatchFinally block; the thrown value is
                 stored in local <local>; and
* Finally: used to start a finally block of TryFinally/TryCatchFinally.

Three different opcodes are used to start a try block to simplify the
AST construction during bytecode parsing.

BUG=

Review-Url: https://codereview.chromium.org/2222193004
Cr-Commit-Position: refs/heads/master@{#38579}

src/flag-definitions.h

@@ -529,6 +529,8 @@ DEFINE_INT(typed_array_max_size_in_heap, 64,
 
 DEFINE_BOOL(wasm_simd_prototype, false,
             "enable prototype simd opcodes for wasm")
+DEFINE_BOOL(wasm_eh_prototype, false,
+            "enable prototype exception handling opcodes for wasm")
 
 // Profiler flags.
 DEFINE_INT(frame_count, 1, "number of stack frames inspected by the profiler")

src/wasm/wasm-opcodes.h

@@ -55,6 +55,12 @@ const WasmCodePosition kNoCodePosition = -1;
   V(BrTable, 0x08, _)             \
   V(Return, 0x09, _)              \
   V(Unreachable, 0x0a, _)         \
+  V(Throw, 0xfa, _)               \
+  V(TryCatch, 0xfb, _)            \
+  V(TryCatchFinally, 0xfc, _)     \
+  V(TryFinally, 0xfd, _)          \
+  V(Catch, 0xfe, _)               \
+  V(Finally, 0xff, _)             \
   V(End, 0x0F, _)
 
 // Constants, locals, globals, and calls.

test/unittests/wasm/ast-decoder-unittest.cc

@@ -1829,6 +1829,91 @@ TEST_F(AstDecoderTest, Select_TypeCheck) {
       WASM_SELECT(WASM_F32(9.9), WASM_GET_LOCAL(0), WASM_I64V_1(0)));
 }
 
+TEST_F(AstDecoderTest, Throw) {
+  FLAG_wasm_eh_prototype = true;
+  EXPECT_VERIFIES_INLINE(sigs.v_i(), WASM_GET_LOCAL(0), kExprThrow);
+
+  // TODO(jpp): can't throw d, f, or l.
+  EXPECT_VERIFIES_INLINE(sigs.i_d(), WASM_GET_LOCAL(0), kExprThrow,
+                         WASM_I32V(0));
+  EXPECT_VERIFIES_INLINE(sigs.i_f(), WASM_GET_LOCAL(0), kExprThrow,
+                         WASM_I32V(0));
+  EXPECT_VERIFIES_INLINE(sigs.l_l(), WASM_GET_LOCAL(0), kExprThrow,
+                         WASM_I64V(0));
+}
+
+#define WASM_CATCH(local) kExprCatch, static_cast<byte>(local)
+TEST_F(AstDecoderTest, TryCatch) {
+  FLAG_wasm_eh_prototype = true;
+  EXPECT_VERIFIES_INLINE(sigs.v_i(), kExprTryCatch, WASM_CATCH(0), kExprEnd);
+
+  // Missing catch.
+  EXPECT_FAILURE_INLINE(sigs.v_v(), kExprTryCatch, kExprEnd);
+
+  // Missing end.
+  EXPECT_FAILURE_INLINE(sigs.v_i(), kExprTryCatch, WASM_CATCH(0));
+
+  // Double catch.
+  EXPECT_FAILURE_INLINE(sigs.v_i(), kExprTryCatch, WASM_CATCH(0), WASM_CATCH(0),
+                        kExprEnd);
+
+  // Unexpected finally.
+  EXPECT_FAILURE_INLINE(sigs.v_i(), kExprTryCatch, WASM_CATCH(0), kExprFinally,
+                        kExprEnd);
+}
+
+TEST_F(AstDecoderTest, TryFinally) {
+  FLAG_wasm_eh_prototype = true;
+  EXPECT_VERIFIES_INLINE(sigs.v_v(), kExprTryFinally, kExprFinally, kExprEnd);
+
+  // Mising finally.
+  EXPECT_FAILURE_INLINE(sigs.v_v(), kExprTryFinally, kExprEnd);
+
+  // Missing end.
+  EXPECT_FAILURE_INLINE(sigs.v_v(), kExprTryFinally, kExprFinally);
+
+  // Double finally.
+  EXPECT_FAILURE_INLINE(sigs.v_v(), kExprTryFinally, kExprFinally, kExprFinally,
+                        kExprEnd);
+
+  // Unexpected catch.
+  EXPECT_FAILURE_INLINE(sigs.v_i(), kExprTryCatch, WASM_CATCH(0), kExprFinally,
+                        kExprEnd);
+}
+
+TEST_F(AstDecoderTest, TryCatchFinally) {
+  FLAG_wasm_eh_prototype = true;
+  EXPECT_VERIFIES_INLINE(sigs.v_i(), kExprTryCatchFinally, WASM_CATCH(0),
+                         kExprFinally, kExprEnd);
+
+  // Missing catch.
+  EXPECT_FAILURE_INLINE(sigs.v_i(), kExprTryCatchFinally, kExprFinally,
+                        kExprEnd);
+
+  // Double catch.
+  EXPECT_FAILURE_INLINE(sigs.v_i(), kExprTryCatchFinally, WASM_CATCH(0),
+                        WASM_CATCH(0), kExprFinally, kExprEnd);
+
+  // Missing finally.
+  EXPECT_FAILURE_INLINE(sigs.v_i(), kExprTryCatchFinally, WASM_CATCH(0),
+                        kExprEnd);
+
+  // Double finally.
+  EXPECT_FAILURE_INLINE(sigs.v_i(), kExprTryCatchFinally, WASM_CATCH(0),
+                        kExprFinally, kExprFinally, kExprEnd);
+
+  // Finally before catch.
+  EXPECT_FAILURE_INLINE(sigs.v_i(), kExprTryCatchFinally, kExprFinally,
+                        WASM_CATCH(0), kExprEnd);
+
+  // Missing both try and finally.
+  EXPECT_FAILURE_INLINE(sigs.v_i(), kExprTryCatchFinally, kExprEnd);
+
+  // Missing end.
+  EXPECT_FAILURE_INLINE(sigs.v_i(), kExprTryCatchFinally, WASM_CATCH(0),
+                        kExprFinally);
+}
+
 class WasmOpcodeLengthTest : public TestWithZone {
  public:
   WasmOpcodeLengthTest() : TestWithZone() {}
@@ -1856,6 +1941,12 @@ TEST_F(WasmOpcodeLengthTest, Statements) {
   EXPECT_LENGTH(1, kExprSelect);
   EXPECT_LENGTH(3, kExprBr);
   EXPECT_LENGTH(3, kExprBrIf);
+  EXPECT_LENGTH(1, kExprThrow);
+  EXPECT_LENGTH(1, kExprTryCatch);
+  EXPECT_LENGTH(1, kExprTryFinally);
+  EXPECT_LENGTH(1, kExprTryCatchFinally);
+  EXPECT_LENGTH(2, kExprCatch);
+  EXPECT_LENGTH(1, kExprFinally);
 }
 
 TEST_F(WasmOpcodeLengthTest, MiscExpressions) {
@@ -2097,6 +2188,13 @@ TEST_F(WasmOpcodeArityTest, Control) {
     EXPECT_ARITY(0, kExprReturn, ARITY_0);
     EXPECT_ARITY(1, kExprReturn, ARITY_1);
   }
+
+  EXPECT_ARITY(0, kExprThrow);
+  EXPECT_ARITY(0, kExprTryCatch);
+  EXPECT_ARITY(0, kExprTryFinally);
+  EXPECT_ARITY(0, kExprTryCatchFinally);
+  EXPECT_ARITY(1, kExprCatch, 2);
+  EXPECT_ARITY(0, kExprFinally);
 }
 
 TEST_F(WasmOpcodeArityTest, Misc) {