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| == Goal ==
| | OdinMonkey was the optimizing AsmJS compiler. |
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| Provide an optimized implementation of the (co-evolvoing) [https://github.com/dherman/asm.js/blob/master/tex/def.pdf asm.js spec] which achieves near-native performance (within 2x of -O2) on JS generated from C/C++ (with the pilot code generator being [https://github.com/kripken/emscripten Emscripten]).
| | [[File:Odinmonkey800.jpg]]<br> |
| | | Credit to John Howard |
| == Status ==
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| It looks like we're getting the expected performance, even without the optimizations in the below section: we're seeing anywhere from 2x to 6x improvements against trunk/v8 on large Emscripten apps. It's to talk to other engines and work toward something land-able (tasks below).
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| The code is currently in https://hg.mozilla.org/users/lwagner_mozilla.com/odinmonkey and works on x64-unix; other platforms are in progress.
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| == Tasks before initial landing ==
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| * Tier 1 platform support (remaining):
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| ** x64 (Windows)
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| ** x86 (Windows, Unix)
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| ** ARM
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| * Fuzz (with decoders mutation-based fuzzer based on existing asm.js programs)
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| * Engine integration:
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| * Super-basic SPS profiler integration (summarize all asm.js code as a single frame)
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| * Don't crash if someone neuters the ArrayBuffer
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| * Audit Odin code for OOM-safety.
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| * Final polish on error messages
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| * Unbreak IonSpew
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| == Further work (after initial landing) ==
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| Optimizations, roughly in priority order:
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| # Optimize asm.js-to-Ion transition with custom-generated exit stub
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| # Investigate why we spend so much time (15%) in ion::ThunkToInterpreter and ion::Bail under FFI calls; these should be trivial functions.
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| # Add DataView to asm.js to allow us to avoid masking on loads/stores
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| #* Measure how much it'll win us (so far, 20% on zlib)
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| #* Signal-handler support
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| #* Investigate this 32-bit/64-bit register slicing issue
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| # Avoid slow-script and stack overflow checks with signal handler support
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| # Add a float32 type to asm.js to allow 32-bit float arithmetic
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| # Optimize idiv (using signal handler for FP exception)
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| # Optimize double-to-int conversion (using signal handler for FP exception)
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| # Full GVN/range analysis support for all the new asm.js IM MIR nodes
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| # ToInt shouldn't generate so much code
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| # Ensure we're emitting the smallest mod/rm encoding for lea/loads/stores on x86 (viz., if displacement is 0).
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| Other work items:
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| * FunctionBlob (TODO: link to proposal)
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| ** Efficient transfer between workers
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| ** Efficient IndexedDB serialization/deserialization
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| * Add a mapping from return pc -> function information
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| ** Use to provide profile information to SPS without dynamic instrumentation.
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| ** Make asm.js calls show up in backtraces (Debugger, StackIter)
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| * Create automatic instrumentation so we can compare, at the basic-block level, how many instructions are executed in both GCC/LLVM-compiled C++ and Odin-compiled asm.js. This should point us directly to our worst codegen pain points.
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| == General IonMonkey optimizations ==
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| * Optimize control flow to minimize jumping (we tend to a lot worse than GCC here since we don't even try to optimize this)
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| ** Rearrange loops to put the condition at the end
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| ** Fold jump-to-jump into single jump
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| ** Reorder blocks to replace jumps with fall-through.
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| * Align loop headers on natural boundaries (I can see GCC doing this, it's also a well-known suggestion)
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| * Align ExecutableAllocator allocations to a 16-byte boundary.
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| * Use 32-bit register encoding on x64 for when the MIRType is int32
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| * Use pc-relative constant double loads instead of trying to use immediates (GCC does, need to measure perf)
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