[LLVMdev] [LLVM Dev] [Discussion] Function-based parallel LLVM backend code generation

[Evan Cheng]

Please see Shuxin's proposal on "parallelizing post-IPO stage". It seems the two projects are related.

Evan

On Jul 16, 2013, at 3:33 AM, "Wan, Xiaofei" <xiaofei.wan at intel.com> wrote:

> Hi, community:
> 
> For the sake of our business need, I want to enable "Function-based parallel code generation" to boost up the compilation of single module, please see the details of the design and provide your feedbacks on below aspects, thanks!
> 1. Is this idea the proper solution for my requirement
> 2. This new feature will be enabled by llc -thd=N and has no impact on original llc when -thd=1
> 3. Can this new feature of llc be accepted by community and merged into LLVM code tree
> 
> Patches
> The patch is divided into four separated parts, the all-in-one patch could be found here:
> http://llvm-reviews.chandlerc.com/D1152
> 
> Design
> https://docs.google.com/document/d/1QSkP6AumMCAVpgzwympD5pI3btPJt4SRgjY-vhyfySg/edit?usp=sharing
> 
> 
> Background
> 1. Our business need to compile C/C++ source files into LLVM IR and link them into a big BC file; the big BC file is then compiled into binary code on different arch/target devices.
> 2. Backend code generation is a time-consuming activity happened on target device which makes it an important user experience.
> 3. Make -j or file based parallelism can't help here since there is only one big BC file; function-based parallel LLVM backend code generation is a good solution to improve compilation time which will fully utilize multi-cores.
> 
> Overall design strategy and goal
> 1. Generate totally same binary as what single thread output
> 2. No impacts on single thread performance & conformance
> 3. Little impacts on LLVM code infrastructure
> 
> Current status and test result
> 1. Parallel llc can generate same code as single thread by "objdump -d", it could pass 10 hours stress test for all performance benchmark
> 2. Parallel llc can introduce ~2.9X performance gain on XEON sever for 4 threads
> 
> 
> Thanks
> Wan Xiaofei
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