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id="docs-internal-guid-9202d6c2-7fff-c9d1-a6ca-df25a96682bb"><font
face="Courier New, Courier, monospace"><span style="font-size: 12pt; color: rgb(0, 0, 0); background-color: transparent; font-weight: 400; font-style: normal; font-variant: normal; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;">Hi all,
</span></font></p>
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face="Courier New, Courier, monospace"><span style="font-size: 12pt; color: rgb(0, 0, 0); background-color: transparent; font-weight: 400; font-style: normal; font-variant: normal; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;">
</span></font></p>
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style="line-height:1.38;margin-top:0pt;margin-bottom:0pt;"><font
face="Courier New, Courier, monospace"><span style="font-size: 12pt; color: rgb(0, 0, 0); background-color: transparent; font-weight: 400; font-style: normal; font-variant: normal; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;">I would like to propose "Speculative compilation support in ORC v2 JIT API" for this year GSoC summer project.</span></font></p>
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face="Courier New, Courier, monospace"><span style="font-size: 12pt; color: rgb(0, 0, 0); background-color: transparent; font-weight: 400; font-style: normal; font-variant: normal; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;">
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style="line-height:1.38;margin-top:0pt;margin-bottom:0pt;"><font
face="Courier New, Courier, monospace"><span style="font-size: 12pt; color: rgb(0, 0, 0); background-color: transparent; font-weight: 400; font-style: normal; font-variant: normal; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;">Project Description: </span></font></p>
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face="Courier New, Courier, monospace"><span style="font-size: 12pt; color: rgb(0, 0, 0); background-color: transparent; font-weight: 400; font-style: normal; font-variant: normal; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;"> </span><span style="font-size: 12pt; color: rgb(0, 0, 0); background-color: transparent; font-weight: 400; font-style: normal; font-variant: normal; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;">Speculative compilation support. One of the selling points of the concurrent ORC APIs is that you can start compiling a function before you need it, in the hope that by the time that you do need it it is already compiled. However, if we just speculatively compile everything we're quickly going to overload our memory/CPU resources, which will be lousy for performance. What we really want to do is to take into account any information we have (from high level program representations, e.g. ASTs or CFGs, or from profiling data from previous executions) to try to guess what functions are worth speculatively compiling next. </span></font></p>
<font face="Courier New, Courier, monospace"><span style="font-size: 12pt; color: rgb(0, 0, 0); background-color: transparent; font-weight: 400; font-style: normal; font-variant: normal; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;">Idea is proposed by Lang Hames.</span></font><font
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face="Courier New, Courier, monospace"><span style="font-size: 12pt; color: rgb(0, 0, 0); background-color: transparent; font-weight: 400; font-style: normal; font-variant: normal; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;">
</span></font></p>
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style="line-height:1.38;margin-top:0pt;margin-bottom:0pt;"><font
face="Courier New, Courier, monospace"><span style="font-size: 12pt; color: rgb(0, 0, 0); background-color: transparent; font-weight: 400; font-style: normal; font-variant: normal; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;">Current Status of ORC v2: </span></font></p>
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<li dir="ltr" style="list-style-type: decimal; font-size: 12pt; color: rgb(0, 0, 0); background-color: transparent; font-weight: 400; font-style: normal; font-variant: normal; text-decoration: none; vertical-align: baseline; white-space: pre; margin-left: 36pt;"><p dir="ltr" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt;"><font face="Courier New, Courier, monospace"><span style="font-size: 12pt; color: rgb(0, 0, 0); background-color: transparent; font-weight: 400; font-style: normal; font-variant: normal; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;">ORC currently supports concurrent compilation and Lazy (on request compilation), trunk contains default new ORC JIT implementations as LLJIT, LLLazyJIT. </span></font></p></li>
<li dir="ltr" style="list-style-type: decimal; font-size: 12pt; color: rgb(0, 0, 0); background-color: transparent; font-weight: 400; font-style: normal; font-variant: normal; text-decoration: none; vertical-align: baseline; white-space: pre; margin-left: 36pt;"><p dir="ltr" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt;"><font face="Courier New, Courier, monospace"><span style="font-size: 12pt; color: rgb(0, 0, 0); background-color: transparent; font-weight: 400; font-style: normal; font-variant: normal; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;">[WIP] Jit-linker a drop-in-replacement for RuntimeDyld atleast for MachO in ORC JIT.</span></font></p></li>
<li dir="ltr" style="list-style-type: decimal; font-size: 12pt; color: rgb(0, 0, 0); background-color: transparent; font-weight: 400; font-style: normal; font-variant: normal; text-decoration: none; vertical-align: baseline; white-space: pre; margin-left: 36pt;"><p dir="ltr" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt;"><font face="Courier New, Courier, monospace"><span style="font-size: 12pt; color: rgb(0, 0, 0); background-color: transparent; font-weight: 400; font-style: normal; font-variant: normal; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;">Primitive code to handle speculative is in trunk. But it needs to refactored & designed to get generalized, simple APIs to support speculation.</span></font></p></li>
<li dir="ltr" style="list-style-type: decimal; font-size: 12pt; color: rgb(0, 0, 0); background-color: transparent; font-weight: 400; font-style: normal; font-variant: normal; text-decoration: none; vertical-align: baseline; white-space: pre; margin-left: 36pt;"><p dir="ltr" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt;"><font face="Courier New, Courier, monospace"><span style="font-size: 12pt; color: rgb(0, 0, 0); background-color: transparent; font-weight: 400; font-style: normal; font-variant: normal; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;">Currently, no heuristics to support speculation in trunk.</span></font></p></li>
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<p dir="ltr"
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face="Courier New, Courier, monospace"><span style="font-size: 12pt; color: rgb(0, 0, 0); background-color: transparent; font-weight: 400; font-style: normal; font-variant: normal; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;">Proposed Solution: </span></font></p>
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<li dir="ltr" style="list-style-type: decimal; font-size: 12pt; color: rgb(0, 0, 0); background-color: transparent; font-weight: 400; font-style: normal; font-variant: normal; text-decoration: none; vertical-align: baseline; white-space: pre; margin-left: 36pt;"><p dir="ltr" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt;"><font face="Courier New, Courier, monospace"><span style="font-size: 12pt; color: rgb(0, 0, 0); background-color: transparent; font-weight: 400; font-style: normal; font-variant: normal; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;">New APIs in ORC v2 to support speculation compilation of LLVM bitcode. LLSpecJIT - subtype of LLJIT, default JIT with speculation support in trunk. </span></font></p></li>
<li dir="ltr" style="list-style-type: decimal; font-size: 12pt; color: rgb(0, 0, 0); background-color: transparent; font-weight: 400; font-style: normal; font-variant: normal; text-decoration: none; vertical-align: baseline; white-space: pre; margin-left: 36pt;"><p dir="ltr" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt;"><font face="Courier New, Courier, monospace"><span style="font-size: 12pt; color: rgb(0, 0, 0); background-color: transparent; font-weight: 400; font-style: normal; font-variant: normal; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;">Heuristics to guide speculation - </span></font></p></li>
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style="line-height:1.38;margin-top:0pt;margin-bottom:0pt;margin-left:
108pt;"><font face="Courier New, Courier, monospace"><span style="font-size: 12pt; color: rgb(0, 0, 0); background-color: transparent; font-weight: 400; font-style: normal; font-variant: normal; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;">Currently, I’m going through some literature/research papers to find good basic heuristics. We can derive useful information from Control flow graphs, IR etc. So far I figured out that </span><span style="font-size: 12pt; color: rgb(0, 0, 0); background-color: transparent; font-weight: 700; font-style: normal; font-variant: normal; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;">Region-based compilation </span><span style="font-size: 12pt; color: rgb(0, 0, 0); background-color: transparent; font-weight: 400; font-style: normal; font-variant: normal; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;">is more appropriate for speculation. Since, unit of compilation (granularity) is key good dynamic compilation, region based compilation address that by forming frequently executed code as a region (unit), this can be basic block, function or group of functions. But since, LLVM JIT API needs interoperates with static compiler, unit of compilation here is a complete module. The plan in mind is to break the module into regions and compile regions speculatively using multiple JIT backend light weight threads. I’m still not sure, how this can be done, I would highly appreciate the feedback from community in deciding the heuristics & granularity to compile.</span></font></p>
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face="Courier New, Courier, monospace"><span style="font-size: 12pt; color: rgb(0, 0, 0); background-color: transparent; font-weight: 400; font-style: normal; font-variant: normal; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;"> </span><span style="font-size: 12pt; color: rgb(0, 0, 0); background-color: transparent; font-weight: 400; font-style: normal; font-variant: normal; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;"> </span><span style="font-size: 12pt; color: rgb(0, 0, 0); background-color: transparent; font-weight: 400; font-style: normal; font-variant: normal; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;">3.Practical example with benchmarks: To my best of knowledge PostgreSQL using ORC API, it would be easier to get postgresql queries to get compile speculatively and compare results with baseline (concurrent compiler without speculation).</span></font></p>
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style="line-height:1.38;margin-top:0pt;margin-bottom:0pt;"><font
face="Courier New, Courier, monospace"><span style="font-size: 12pt; color: rgb(0, 0, 0); background-color: transparent; font-weight: 400; font-style: normal; font-variant: normal; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;"> </span><span style="font-size: 12pt; color: rgb(0, 0, 0); background-color: transparent; font-weight: 400; font-style: normal; font-variant: normal; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;"> </span><span style="font-size: 12pt; color: rgb(0, 0, 0); background-color: transparent; font-weight: 400; font-style: normal; font-variant: normal; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;">4. Unit tests + documentation.</span></font></p>
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face="Courier New, Courier, monospace"><span style="font-size: 12pt; color: rgb(0, 0, 0); background-color: transparent; font-weight: 400; font-style: normal; font-variant: normal; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;">Benefits:</span><span style="font-size: 12pt; color: rgb(0, 0, 0); background-color: transparent; font-weight: 400; font-style: normal; font-variant: normal; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;"> </span></font></p>
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<li dir="ltr" style="list-style-type: decimal; font-size: 12pt; color: rgb(0, 0, 0); background-color: transparent; font-weight: 400; font-style: normal; font-variant: normal; text-decoration: none; vertical-align: baseline; white-space: pre; margin-left: 72pt;"><p dir="ltr" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt;"><font face="Courier New, Courier, monospace"><span style="font-size: 12pt; color: rgb(0, 0, 0); background-color: transparent; font-weight: 400; font-style: normal; font-variant: normal; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;">We can full use of multiple compilation threads, to compile code upfront with minimum false positive. </span></font></p></li>
<li dir="ltr" style="list-style-type: decimal; font-size: 12pt; color: rgb(0, 0, 0); background-color: transparent; font-weight: 400; font-style: normal; font-variant: normal; text-decoration: none; vertical-align: baseline; white-space: pre; margin-left: 72pt;"><p dir="ltr" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt;"><font face="Courier New, Courier, monospace"><span style="font-size: 12pt; color: rgb(0, 0, 0); background-color: transparent; font-weight: 400; font-style: normal; font-variant: normal; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;">Stabilize JIT APIs which most clients looking for when transitioning to newer versions.</span></font></p></li>
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<p dir="ltr"
style="line-height:1.38;margin-top:0pt;margin-bottom:0pt;"><font
face="Courier New, Courier, monospace"><span style="font-size: 12pt; color: rgb(0, 0, 0); background-color: transparent; font-weight: 400; font-style: normal; font-variant: normal; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;">Further Opportunities : </span></font></p>
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style="line-height:1.38;margin-top:0pt;margin-bottom:0pt;"><font
face="Courier New, Courier, monospace"><span style="font-size: 12pt; color: rgb(0, 0, 0); background-color: transparent; font-weight: 400; font-style: normal; font-variant: normal; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;">We can also use thinlto summaries in module to decide which code is worthier to compile next, based on this lighting </span><a
href="https://www.youtube.com/watch?v=ZCnHxRhQmvs"
style="text-decoration:none;"><span style="font-size: 12pt; color: rgb(17, 85, 204); background-color: transparent; font-weight: 400; font-style: normal; font-variant: normal; text-decoration: underline; vertical-align: baseline; white-space: pre-wrap;">LLVM Dev talk by Stefan</span></a><span style="font-size: 12pt; color: rgb(0, 0, 0); background-color: transparent; font-weight: 400; font-style: normal; font-variant: normal; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;">. </span></font></p>
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face="Courier New, Courier, monospace"><span style="font-size: 12pt; color: rgb(0, 0, 0); background-color: transparent; font-weight: 400; font-style: normal; font-variant: normal; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;">Profile guided optimization - information will be helpful in this, provide further room for improvement.</span></font></p>
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style="line-height:1.38;margin-top:0pt;margin-bottom:0pt;"><font
face="Courier New, Courier, monospace"><span style="font-size: 12pt; color: rgb(0, 0, 0); background-color: transparent; font-weight: 400; font-style: normal; font-variant: normal; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;"> </span></font></p>
<p dir="ltr"
style="line-height:1.38;margin-top:0pt;margin-bottom:0pt;"><font
face="Courier New, Courier, monospace"><span style="font-size: 12pt; color: rgb(0, 0, 0); background-color: transparent; font-weight: 400; font-style: normal; font-variant: normal; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;">I would highly appreciate the community feedback & suggestions :)
</span></font></p>
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style="line-height:1.38;margin-top:0pt;margin-bottom:0pt;"><font
face="Courier New, Courier, monospace"><span style="font-size: 12pt; color: rgb(0, 0, 0); background-color: transparent; font-weight: 400; font-style: normal; font-variant: normal; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;">I will try my best to address all the comments in the proposal. I'm currently familiarizing myself with new APIs and learning heuristics. I will try to get the draft proposal by next week.</span></font></p>
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face="Courier New, Courier, monospace"><span style="font-size: 12pt; color: rgb(0, 0, 0); background-color: transparent; font-weight: 400; font-style: normal; font-variant: normal; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;">
</span></font></p>
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style="line-height:1.38;margin-top:0pt;margin-bottom:0pt;"><font
face="Courier New, Courier, monospace"><span style="font-size: 12pt; color: rgb(0, 0, 0); background-color: transparent; font-weight: 400; font-style: normal; font-variant: normal; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;">References: HHVM JIT: A profile-Guided, Region-Based Compiler for PHP & Hack [<a moz-do-not-send="true" href="https://dl.acm.org/citation.cfm?id=3192374">paper</a>].</span></font></p>
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style="line-height:1.38;margin-top:0pt;margin-bottom:0pt;"><font
face="Courier New, Courier, monospace"><span style="font-size: 12pt; color: rgb(0, 0, 0); background-color: transparent; font-weight: 400; font-style: normal; font-variant: normal; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;">PostgreSQL [<a moz-do-not-send="true" href="https://doxygen.postgresql.org/structLLVMJitHandle.html">JIT</a>]
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face="Courier New, Courier, monospace"><span style="font-size: 12pt; color: rgb(0, 0, 0); background-color: transparent; font-weight: 400; font-style: normal; font-variant: normal; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;">Execution Engine [<a moz-do-not-send="true" href="https://reviews.llvm.org/diffusion/L/browse/llvm/trunk/lib/ExecutionEngine/Orc/">ORC</a>]
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<pre class="moz-signature" cols="72"><font face="Courier New, Courier, monospace">--
Have a great day!
PreeJackie</font></pre>
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