[PATCH] If a conditional branch jumps to the same target, remove the condition

[Hal Finkel]

----- Original Message -----
> From: "Philip Reames" <listmail at philipreames.com>
> To: reviews+D8220+public+8ff214d7d1b26317 at reviews.llvm.org, hfinkel at anl.gov
> Cc: llvm-commits at cs.uiuc.edu
> Sent: Tuesday, March 10, 2015 5:12:28 PM
> Subject: Re: [PATCH] If a conditional branch jumps to the same target, remove the condition
> 
> @Hal - Unless I'm missing something, this is already handled in
> ConstantFoldTerminator.
> 
>      if (Dest2 == Dest1) {       // Conditional branch to same
>      location?
>        // This branch matches something like this:
>        //     br bool %cond, label %Dest, label %Dest
>        // and changes it into:  br label %Dest
> 
>        // Let the basic block know that we are letting go of one copy
>        of it.
>        assert(BI->getParent() && "Terminator not inserted in
>        block!");
>        Dest1->removePredecessor(BI->getParent());
> 
>        // Replace the conditional branch with an unconditional one.
>        Builder.CreateBr(Dest1);
>        Value *Cond = BI->getCondition();
>        BI->eraseFromParent();
>        if (DeleteDeadConditions)
>          RecursivelyDeleteTriviallyDeadInstructions(Cond, TLI);
>        return true;
>      }
> 
> Given this, I plan to submit as is.

Heh; indeed. Missed that. Sounds good, thanks!

 -Hal

> 
> On 03/10/2015 01:43 PM, hfinkel at anl.gov wrote:
> > LGTM. But, could you also please fix llvm::ConstantFoldTerminator
> > in lib/Transforms/Utils/Local.cpp so that it handles the undef
> > condition and transforms the branch with the undef condition into
> > an unconditional branch. If we don't want to do that, then we
> > should just pick true/false here instead of using undef.
> >
> >
> > http://reviews.llvm.org/D8220
> >
> > EMAIL PREFERENCES
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> >
> >
> 
> 

-- 
Hal Finkel
Assistant Computational Scientist
Leadership Computing Facility
Argonne National Laboratory