diff -r 000000000000 -r 6474c204b198 js/src/jit/JSONSpewer.h
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/js/src/jit/JSONSpewer.h	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,77 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
+ * vim: set ts=8 sts=4 et sw=4 tw=99:
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef jit_JSONSpewer_h
+#define jit_JSONSpewer_h
+
+#include "mozilla/NullPtr.h"
+
+#include <stdio.h>
+
+#include "js/TypeDecls.h"
+
+namespace js {
+namespace jit {
+
+class MDefinition;
+class MInstruction;
+class MBasicBlock;
+class MIRGraph;
+class MResumePoint;
+class LinearScanAllocator;
+class LInstruction;
+
+class JSONSpewer
+{
+  private:
+    // Set by beginFunction(); unset by endFunction().
+    // Used to correctly format output in case of abort during compilation.
+    bool inFunction_;
+
+    int indentLevel_;
+    bool first_;
+    FILE *fp_;
+
+    void indent();
+
+    void property(const char *name);
+    void beginObject();
+    void beginObjectProperty(const char *name);
+    void beginListProperty(const char *name);
+    void stringValue(const char *format, ...);
+    void stringProperty(const char *name, const char *format, ...);
+    void integerValue(int value);
+    void integerProperty(const char *name, int value);
+    void endObject();
+    void endList();
+
+  public:
+    JSONSpewer()
+      : inFunction_(false),
+        indentLevel_(0),
+        first_(true),
+        fp_(nullptr)
+    { }
+    ~JSONSpewer();
+
+    bool init(const char *path);
+    void beginFunction(JSScript *script);
+    void beginPass(const char * pass);
+    void spewMDef(MDefinition *def);
+    void spewMResumePoint(MResumePoint *rp);
+    void spewMIR(MIRGraph *mir);
+    void spewLIns(LInstruction *ins);
+    void spewLIR(MIRGraph *mir);
+    void spewIntervals(LinearScanAllocator *regalloc);
+    void endPass();
+    void endFunction();
+    void finish();
+};
+
+} // namespace jit
+} // namespace js
+
+#endif /* jit_JSONSpewer_h */