[llvm-dev] Performace regression in llvm::ExecutionEngine::finalizeObject (original) (raw)

Lang Hames via llvm-dev llvm-dev at lists.llvm.org
Tue Jul 14 17:09:45 PDT 2020

Hi Gaurav,

I don't think the default JIT optimization settings for ExecutionEngine have changed, so if you didn't change your JIT config either then this probably isn't a JIT bug.

Was the whole of the regression due to slowdowns in PerformDAGCombine? Was there any substantial change to the IR coming in to CodeGen between LLVM 8 and LLVM 10 for your test case?

If you don't find answers in this thread I'd be inclined to ask again and phrase it as a CodeGen regression question: That might catch more people's attention.

Regards, Lang.

On Thu, Jun 25, 2020 at 9:49 AM gaurav phatnani via llvm-dev < llvm-dev at lists.llvm.org> wrote:

Hello,

I am working on upgrading an app from using llvm 8.0.1 to llvm 10.0. I create a JIT llvm::ExecutionEngine(i386 CPU, NONE codegenopt) which contains a single module. Below are some numbers for call to llvm::ExecutionEngine::finalizeObject: llvm 8.0.1 - less than 0.5 seconds llvm 10.0 - greater than 170 seconds Using Vtune, was able to trace the regression to llvm::SDNode::hasNUsesOfValue(which is called by llvm::X86TargetLowering::PerformDAGCombine) I want to check if anyone has faced a similar problem or has any ideas what the root cause/fix might be? Thanks, Gaurav

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