[ubsan][compiler] Avoid out-of-range casts to IrOpcode::Value

An enum-typed value should never have a value outside of that enum's
range.
This patch enforces that in Debug mode, while in Release mode keeping
the previous behavior of returning "UnknownOpcode" as the mnemonic for
illegal IrOpcode values to ease debugging.

Bug: v8:3770
Change-Id: I83a5a356f1fb7a266921940a4495f1d39a1823cd
Reviewed-on: https://chromium-review.googlesource.com/c/1436221Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Commit-Queue: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#59102}

src/compiler/opcodes.cc

@@ -26,6 +26,8 @@ char const* const kMnemonics[] = {
 
 // static
 char const* IrOpcode::Mnemonic(Value value) {
+  DCHECK_LE(0, static_cast<int>(value));
+  DCHECK_LE(static_cast<int>(value), IrOpcode::Value::kLast);
   size_t const n = std::min<size_t>(value, arraysize(kMnemonics) - 1);
   return kMnemonics[n];
 }

test/unittests/compiler/opcodes-unittest.cc

@@ -78,9 +78,6 @@ bool IsComparisonOpcode(IrOpcode::Value opcode) {
   }
 }
 
-
-const IrOpcode::Value kInvalidOpcode = static_cast<IrOpcode::Value>(123456789);
-
 char const* const kMnemonics[] = {
 #define OPCODE(Opcode) #Opcode,
     ALL_OP_LIST(OPCODE)
@@ -96,42 +93,36 @@ const IrOpcode::Value kOpcodes[] = {
 }  // namespace
 
 TEST(IrOpcodeTest, IsCommonOpcode) {
-  EXPECT_FALSE(IrOpcode::IsCommonOpcode(kInvalidOpcode));
   TRACED_FOREACH(IrOpcode::Value, opcode, kOpcodes) {
     EXPECT_EQ(IsCommonOpcode(opcode), IrOpcode::IsCommonOpcode(opcode));
   }
 }
 
 TEST(IrOpcodeTest, IsControlOpcode) {
-  EXPECT_FALSE(IrOpcode::IsControlOpcode(kInvalidOpcode));
   TRACED_FOREACH(IrOpcode::Value, opcode, kOpcodes) {
     EXPECT_EQ(IsControlOpcode(opcode), IrOpcode::IsControlOpcode(opcode));
   }
 }
 
 TEST(IrOpcodeTest, IsJsOpcode) {
-  EXPECT_FALSE(IrOpcode::IsJsOpcode(kInvalidOpcode));
   TRACED_FOREACH(IrOpcode::Value, opcode, kOpcodes) {
     EXPECT_EQ(IsJsOpcode(opcode), IrOpcode::IsJsOpcode(opcode));
   }
 }
 
 TEST(IrOpcodeTest, IsConstantOpcode) {
-  EXPECT_FALSE(IrOpcode::IsConstantOpcode(kInvalidOpcode));
   TRACED_FOREACH(IrOpcode::Value, opcode, kOpcodes) {
     EXPECT_EQ(IsConstantOpcode(opcode), IrOpcode::IsConstantOpcode(opcode));
   }
 }
 
 TEST(IrOpcodeTest, IsComparisonOpcode) {
-  EXPECT_FALSE(IrOpcode::IsComparisonOpcode(kInvalidOpcode));
   TRACED_FOREACH(IrOpcode::Value, opcode, kOpcodes) {
     EXPECT_EQ(IsComparisonOpcode(opcode), IrOpcode::IsComparisonOpcode(opcode));
   }
 }
 
 TEST(IrOpcodeTest, Mnemonic) {
-  EXPECT_STREQ("UnknownOpcode", IrOpcode::Mnemonic(kInvalidOpcode));
   TRACED_FOREACH(IrOpcode::Value, opcode, kOpcodes) {
     EXPECT_STREQ(kMnemonics[opcode], IrOpcode::Mnemonic(opcode));
   }