[llvm] r288655 - TableGen/AsmMatcherEmitter: Trust that stable_sort works

[Davide Italiano via llvm-commits]

On Mon, Dec 5, 2016 at 12:15 AM, Matthias Braun via llvm-commits
<llvm-commits at lists.llvm.org> wrote:
> Author: matze
> Date: Mon Dec  5 02:15:57 2016
> New Revision: 288655
>
> URL: http://llvm.org/viewvc/llvm-project?rev=288655&view=rev
> Log:
> TableGen/AsmMatcherEmitter: Trust that stable_sort works
>
> A debug build of AsmMatcherEmitter would use a quadratic algorithm to
> check whether std::stable_sort() actually sorted. Let's hope the authors
> of our C++ standard library did that testing for us. Removing the check
> gives a 3x speedup in the X86 case.
>
> Modified:
>     llvm/trunk/utils/TableGen/AsmMatcherEmitter.cpp
>
> Modified: llvm/trunk/utils/TableGen/AsmMatcherEmitter.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/utils/TableGen/AsmMatcherEmitter.cpp?rev=288655&r1=288654&r2=288655&view=diff
> ==============================================================================
> --- llvm/trunk/utils/TableGen/AsmMatcherEmitter.cpp (original)
> +++ llvm/trunk/utils/TableGen/AsmMatcherEmitter.cpp Mon Dec  5 02:15:57 2016
> @@ -2719,16 +2719,6 @@ void AsmMatcherEmitter::run(raw_ostream
>                        const std::unique_ptr<MatchableInfo> &b){
>                       return *a < *b;});
>
> -#ifndef NDEBUG
> -  // Verify that the table is now sorted
> -  for (auto I = Info.Matchables.begin(), E = Info.Matchables.end(); I != E;
> -       ++I) {
> -    for (auto J = I; J != E; ++J) {
> -      assert(!(**J < **I));
> -    }
> -  }
> -#endif // NDEBUG
> -
>    DEBUG_WITH_TYPE("instruction_info", {
>        for (const auto &MI : Info.Matchables)
>          MI->dump();
>

Thanks for your performance work, it's really appreciated.
That said, maybe instead of removing the check altogether you can just
move it under `LLVM_ENABLE_EXPENSIVE_CHECKS`?

Cheers,

-- 
Davide