[wasm] ASM-2-WASM. Enforces switch default clause appearing last.

src/asmjs/asm-typer.cc

 // Copyright 2016 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/asmjs/asm-typer.h"
 
 #include <limits>
 #include <string>
 
 #include "src/v8.h"
@@ skipping 1237 matching lines @@
 // No need to handle these here -- see the AsmTyper's definition.
 
 // 6.5.10 SwitchStatement
 AsmType* AsmTyper::ValidateSwitchStatement(SwitchStatement* stmt) {
   AsmType* cond_type;
   RECURSE(cond_type = ValidateExpression(stmt->tag()));
   if (!cond_type->IsA(AsmType::Signed())) {
     FAIL(stmt, "Switch tag must be signed.");
   }
 
-  bool has_default = false;
-
+  int default_pos = kNoSourcePosition;
+  int last_case_pos = kNoSourcePosition;
   ZoneSet<int32_t> cases_seen(zone_);
   for (auto* a_case : *stmt->cases()) {
     if (a_case->is_default()) {
-      CHECK(!has_default);
+      CHECK(default_pos == kNoSourcePosition);
       RECURSE(ValidateDefault(a_case));
-      has_default = true;
+      default_pos = a_case->position();
       continue;
     }
 
+    if (last_case_pos == kNoSourcePosition) {
+      last_case_pos = a_case->position();
+    } else {
+      last_case_pos = std::max(last_case_pos, a_case->position());
+    }
+
     int32_t case_lbl;
     RECURSE(ValidateCase(a_case, &case_lbl));
     auto case_lbl_pos = cases_seen.find(case_lbl);
     if (case_lbl_pos != cases_seen.end() && *case_lbl_pos == case_lbl) {
       FAIL(a_case, "Duplicated case label.");
     }
     cases_seen.insert(case_lbl);
   }
 
   if (!cases_seen.empty()) {
     const int64_t max_lbl = *cases_seen.rbegin();
     const int64_t min_lbl = *cases_seen.begin();
     if (max_lbl - min_lbl > std::numeric_limits<int32_t>::max()) {
       FAIL(stmt, "Out-of-bounds case label range.");
     }
   }
 
+  if (last_case_pos != kNoSourcePosition && default_pos != kNoSourcePosition &&
+      default_pos < last_case_pos) {
+    FAIL(stmt, "Switch default must appear last.");
+  }
+
   return AsmType::Void();
 }
 
 // 6.6 ValidateCase
 namespace {
 bool ExtractInt32CaseLabel(CaseClause* clause, int32_t* lbl) {
   auto* lbl_expr = clause->label()->AsLiteral();
 
   if (lbl_expr == nullptr) {
     return false;
@@ skipping 1339 matching lines @@
     return true;
   }
 
   *error_message = typer.error_message();
   return false;
 }
 
 }  // namespace wasm
 }  // namespace internal
 }  // namespace v8