[llvm] r324557 - gold-plugin: Do not set codegen opt level based on LTO opt level.

[Chad Rosier via llvm-commits]

Peter/Rafael,

Over the past few days I've been investigating several regressions with 
our weekly LTO configuration.  As a result, I identified that the 
following regressions were due to this commit:

SPEC2006/h264ref: -2.68%
SPEC2006/libquantum: -4.36%
SPEC2006/perlbench: -2.67%
SPEC2017/mcf: -4.47%
SPEC2017/perlbench: -3.82%

I did not test SPEC2000, SPEC2006fp, or SPEC2017fp, but I'm seeing 
similar small regressions in our weekly runs there as well (i.e., the 
above is just what I was able to test last night, but isn't likely the 
only regressions).  I'd like to kindly request that this change be 
reverted until something is in place to properly propagate the codegen 
optimization level.

  Chad


On 2/7/2018 9:41 PM, Peter Collingbourne via llvm-commits wrote:
> Author: pcc
> Date: Wed Feb  7 18:41:22 2018
> New Revision: 324557
>
> URL: http://llvm.org/viewvc/llvm-project?rev=324557&view=rev
> Log:
> gold-plugin: Do not set codegen opt level based on LTO opt level.
>
> The LTO opt level should not affect the codegen opt level, and indeed
> it does not affect it in lld. Ideally the codegen opt level should
> be controlled by an IR-level attribute based on the compile-time opt
> level, but that hasn't been implemented yet.
>
> Differential Revision: https://reviews.llvm.org/D43040
>
> Modified:
>      llvm/trunk/tools/gold/gold-plugin.cpp
>
> Modified: llvm/trunk/tools/gold/gold-plugin.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/tools/gold/gold-plugin.cpp?rev=324557&r1=324556&r2=324557&view=diff
> ==============================================================================
> --- llvm/trunk/tools/gold/gold-plugin.cpp (original)
> +++ llvm/trunk/tools/gold/gold-plugin.cpp Wed Feb  7 18:41:22 2018
> @@ -727,20 +727,6 @@ static int getOutputFileName(StringRef I
>     return FD;
>   }
>   
> -static CodeGenOpt::Level getCGOptLevel() {
> -  switch (options::OptLevel) {
> -  case 0:
> -    return CodeGenOpt::None;
> -  case 1:
> -    return CodeGenOpt::Less;
> -  case 2:
> -    return CodeGenOpt::Default;
> -  case 3:
> -    return CodeGenOpt::Aggressive;
> -  }
> -  llvm_unreachable("Invalid optimization level");
> -}
> -
>   /// Parse the thinlto_prefix_replace option into the \p OldPrefix and
>   /// \p NewPrefix strings, if it was specified.
>   static void getThinLTOOldAndNewPrefix(std::string &OldPrefix,
> @@ -767,7 +753,6 @@ static std::unique_ptr<LTO> createLTO(In
>   
>     Conf.MAttrs = MAttrs;
>     Conf.RelocModel = RelocationModel;
> -  Conf.CGOptLevel = getCGOptLevel();
>     Conf.DisableVerify = options::DisableVerify;
>     Conf.OptLevel = options::OptLevel;
>     if (options::Parallelism)
>
>
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