[llvm] r220345 - LTO: respect command-line options that disable vectorization.

[JF Bastien]

OK, I think I understand your suggestion and it sounds good. Are you
sending the patch?

On Fri, Oct 24, 2014 at 9:16 AM, Arnold Schwaighofer <
aschwaighofer at apple.com> wrote:

> It is complicated :).
>
> clang turns on/off vectorization through explicitly setting the
> PassManager::LoopVectorize/SLPVectorize fields. This overrides the cl:opt
> flags. Changing the cl::opt default won’t have any effect on clang.
>
> Changing the default will only effect LTO because libLTO does not
> explicitly set the PassManager::LoopVectorize flag but that value gets
> initialized by the cl::opt value.
>
> I am suggesting changing to:
>
>
> static cl::opt<bool>
> RunLoopVectorization("vectorize-loops", cl::Hidden, cl::init(true),
>                      cl::desc("Run the Loop vectorization passes"));
>
> Similar for the slp flag.
>
> We will have to force disabling loop unrolling in the loop vectorizer so
> that we get the behavior before your patch:
>
>   PM.add(createLoopVectorizePass(true, LoopVectorize));
>
>
>
> > On Oct 24, 2014, at 9:03 AM, JF Bastien <jfb at google.com> wrote:
> >
> > Yes, cl::opt<bool> defaults to false when there's no init. Changing the
> default will affect non-LTO too. This may be the right thing to do, but
> isn't my call. Turning it on only for LTO sounds better IMO, but I'm not
> sure what you're suggesting: I think there shouldn't be a vectorization
> flags that are different for LTO and for non-LTO.
> >
> > On Fri, Oct 24, 2014 at 8:57 AM, Arnold Schwaighofer <
> aschwaighofer at apple.com> wrote:
> > JF are you sure that “LoopVectorize” is set to true by default by the
> PassManager instance of libLTO?
> >
> > The reason why I forced these parameters to true is that this is not the
> case if I remember correctly.
> >
> > We wanted the default for libLTO to be with vectorization.
> >
> > PassManager.cpp:
> >
> > static cl::opt<bool>
> > RunLoopVectorization("vectorize-loops", cl::Hidden,
> >                      cl::desc("Run the Loop vectorization passes"));
> >
> > PassManagerBuilder::PassManagerBuilder() {
> >     OptLevel = 2;
> >     SizeLevel = 0;
> >     LibraryInfo = nullptr;
> >     Inliner = nullptr;
> >     DisableTailCalls = false;
> >     DisableUnitAtATime = false;
> >     DisableUnrollLoops = false;
> >     BBVectorize = RunBBVectorization;
> >     SLPVectorize = RunSLPVectorization;
> >     LoopVectorize = RunLoopVectorization;
> >     RerollLoops = RunLoopRerolling;
> >     LoadCombine = RunLoadCombine;
> >     DisableGVNLoadPRE = false;
> >     VerifyInput = false;
> >     VerifyOutput = false;
> >     StripDebug = false;
> >     MergeFunctions = false;
> > }
> >
> > LTOCodeGenerator.cpp:
> >
> > /// Optimize merged modules using various IPO passes
> > bool LTOCodeGenerator::generateObjectFile(raw_ostream &out,
> >                                           bool DisableOpt,
> >                                           bool DisableInline,
> >                                           bool DisableGVNLoadPRE,
> >                                           std::string &errMsg) {
> >   if (!this->determineTarget(errMsg))
> >     return false;
> >
> >   Module *mergedModule = IRLinker.getModule();
> >
> >   // Mark which symbols can not be internalized
> >   this->applyScopeRestrictions();
> >
> >   // Instantiate the pass manager to organize the passes.
> >   PassManager passes;
> >
> >   // Add an appropriate DataLayout instance for this module...
> >
>  mergedModule->setDataLayout(TargetMach->getSubtargetImpl()->getDataLayout());
> >
> >   Triple TargetTriple(TargetMach->getTargetTriple());
> >   PassManagerBuilder PMB;
> >   PMB.DisableGVNLoadPRE = DisableGVNLoadPRE;
> >   if (!DisableInline)
> >     PMB.Inliner = createFunctionInliningPass();
> >   PMB.LibraryInfo = new TargetLibraryInfo(TargetTriple);
> >   if (DisableOpt)
> >     PMB.OptLevel = 0;
> >   PMB.VerifyInput = true;
> >   PMB.VerifyOutput = true;
> >
> >   PMB.populateLTOPassManager(passes, TargetMach);
> >
> >
> >
> > I think cl::opt<bool> defaults to false and your commit effectively
> disabled vectorization during LTO. We can recover this by changing the
> default cl::opt flags 'vectorize-loops’ and 'vectorize-slp'  to true. If
> that does not work (because we make assumption somewhere about the default
> being false) we can follow the example of “DisableGVNLoadPRE” in
> LTOCodeGenerator.cpp and a a flag to disable Vectorization during LTO and
> pass that to the PassManager created in generateObjectFile.
> >
> >   PMB.LoopVectorize = !DisableLTOVectorization;
> >
> >
> > Thanks,
> > Arnold
> >
> > > DisableUnrollLoops
> > > On Oct 24, 2014, at 5:27 AM, Alexey Volkov <avolkov.intel at gmail.com>
> wrote:
> > >
> > > Hi JF,
> > >
> > > After your commit I saw a performance regression because of disabled
> Loop Vectorizer:
> > >  LV: Not vectorizing: No #pragma vectorize enable.
> > > It is really strange since I used -Ofast -flto clang's options to
> build an application.
> > > Before this change loop was successfully vectorized by Loop Vectorizer.
> > >
> > > Thanks, Alexey.
> > >
> > > 2014-10-22 3:18 GMT+04:00 JF Bastien <jfb at google.com>:
> > > Author: jfb
> > > Date: Tue Oct 21 18:18:21 2014
> > > New Revision: 220345
> > >
> > > URL: http://llvm.org/viewvc/llvm-project?rev=220345&view=rev
> > > Log:
> > > LTO: respect command-line options that disable vectorization.
> > >
> > > Summary: Patches 202051 and 208013 added calls to LTO's PassManager
> which unconditionally add LoopVectorizePass and SLPVectorizerPass instead
> of following the logic in PassManagerBuilder::populateModulePassManager and
> honoring the -vectorize-loops -run-slp-after-loop-vectorization flags.
> > >
> > > Reviewers: nadav, aschwaighofer, yijiang
> > >
> > > Subscribers: llvm-commits
> > >
> > > Differential Revision: http://reviews.llvm.org/D5884
> > >
> > > Modified:
> > >     llvm/trunk/lib/Transforms/IPO/PassManagerBuilder.cpp
> > >
> > > Modified: llvm/trunk/lib/Transforms/IPO/PassManagerBuilder.cpp
> > > URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/IPO/PassManagerBuilder.cpp?rev=220345&r1=220344&r2=220345&view=diff
> > >
> ==============================================================================
> > > --- llvm/trunk/lib/Transforms/IPO/PassManagerBuilder.cpp (original)
> > > +++ llvm/trunk/lib/Transforms/IPO/PassManagerBuilder.cpp Tue Oct 21
> 18:18:21 2014
> > > @@ -440,10 +440,12 @@ void PassManagerBuilder::addLTOOptimizat
> > >    // More loops are countable; try to optimize them.
> > >    PM.add(createIndVarSimplifyPass());
> > >    PM.add(createLoopDeletionPass());
> > > -  PM.add(createLoopVectorizePass(true, true));
> > > +  PM.add(createLoopVectorizePass(DisableUnrollLoops, LoopVectorize));
> > >
> > >    // More scalar chains could be vectorized due to more alias
> information
> > > -  PM.add(createSLPVectorizerPass()); // Vectorize parallel scalar
> chains.
> > > +  if (RunSLPAfterLoopVectorization)
> > > +    if (SLPVectorize)
> > > +      PM.add(createSLPVectorizerPass()); // Vectorize parallel scalar
> chains.
> > >
> > >    // After vectorization, assume intrinsics may tell us more about
> pointer
> > >    // alignments.
> > >
> > >
> > > _______________________________________________
> > > llvm-commits mailing list
> > > llvm-commits at cs.uiuc.edu
> > > http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits
> > >
> > >
> > >
> > > --
> > > Alexey Volkov
> > > Intel Corporation
> > > _______________________________________________
> > > llvm-commits mailing list
> > > llvm-commits at cs.uiuc.edu
> > > http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits
> >
> >
>
>
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