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

src/asmjs/asm-typer.cc

Index: src/asmjs/asm-typer.cc
diff --git a/src/asmjs/asm-typer.cc b/src/asmjs/asm-typer.cc
index 165ef9e148faf65e0b4e29701d7ba9b5edf97d07..076cd4db9da0084a71087c564a1dab394aed04b3 100644
--- a/src/asmjs/asm-typer.cc
+++ b/src/asmjs/asm-typer.cc
@@ -1255,17 +1255,23 @@ AsmType* AsmTyper::ValidateSwitchStatement(SwitchStatement* stmt) {
     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);
@@ -1283,6 +1289,11 @@ AsmType* AsmTyper::ValidateSwitchStatement(SwitchStatement* stmt) {
     }
   }
 
+  if (last_case_pos != kNoSourcePosition && default_pos != kNoSourcePosition &&
+      default_pos < last_case_pos) {
+    FAIL(stmt, "Switch default must appear last.");
+  }
+
   return AsmType::Void();
 }