Bug 1355046 - Don't reset column and line info when emitting useless statements in BCE. (r=jorendorff)

js/src/frontend/BytecodeEmitter.cpp

@@ -9134,8 +9134,6 @@ BytecodeEmitter::emitStatement(ParseNode* pn)
                     return false;
             }
         } else {
-            current->currentLine = parser.tokenStream().srcCoords.lineNum(pn2->pn_pos.begin);
-            current->lastColumn = 0;
             if (!reportExtraWarning(pn2, JSMSG_USELESS_EXPR))
                 return false;
         }

js/src/frontend/BytecodeEmitter.h

@@ -191,9 +191,20 @@ struct MOZ_STACK_CLASS BytecodeEmitter
         BytecodeVector code;        /* bytecode */
         SrcNotesVector notes;       /* source notes, see below */
         ptrdiff_t   lastNoteOffset; /* code offset for last source note */
-        uint32_t    currentLine;    /* line number for tree-based srcnote gen */
-        uint32_t    lastColumn;     /* zero-based column index on currentLine of
-                                       last SRC_COLSPAN-annotated opcode */
+
+        // Line number for srcnotes.
+        //
+        // WARNING: If this becomes out of sync with already-emitted srcnotes,
+        // we can get undefined behavior.
+        uint32_t    currentLine;
+
+        // Zero-based column index on currentLine of last SRC_COLSPAN-annotated
+        // opcode.
+        //
+        // WARNING: If this becomes out of sync with already-emitted srcnotes,
+        // we can get undefined behavior.
+        uint32_t    lastColumn;
+
         JumpTarget lastTarget;      // Last jump target emitted.
 
         EmitSection(JSContext* cx, uint32_t lineNum)

js/src/jit-test/tests/parser/bug-1355046.js

@@ -0,0 +1,8 @@
+// |jit-test| error: ReferenceError
+
+var localstr = "";
+for (var i = 0; i < 0xFFFC; ++i)
+  localstr += ('\f') + i + "; ";
+var arg = "x";
+var body = localstr + "for (var i = 0; i < 4; ++i) arr[i](x-1);";
+(new Function(arg, body))(1000);