[llvm-commits] [llvm] r132806 - /llvm/trunk/lib/CodeGen/TailDuplication.cpp

[Bob Wilson]

On Jun 9, 2011, at 2:43 PM, Rafael Espindola wrote:

> Author: rafael
> Date: Thu Jun  9 16:43:25 2011
> New Revision: 132806
> 
> URL: http://llvm.org/viewvc/llvm-project?rev=132806&view=rev
> Log:
> AnalyzeBranch modifies the bb, but we don't want to modify a bb with
> eh edges. Swap the order of the checks to avoid it.

Maybe it would be better to call AnalyzeBranch with AllowModify=false?  At least for the early tail-dup pass, I don't see why this code needs to let AnalyzeBranch modify the code.  I doubt if the late tail-dup pass benefits much, either.

One more comment below....

> 
> Modified:
>    llvm/trunk/lib/CodeGen/TailDuplication.cpp
> 
> Modified: llvm/trunk/lib/CodeGen/TailDuplication.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/TailDuplication.cpp?rev=132806&r1=132805&r2=132806&view=diff
> ==============================================================================
> --- llvm/trunk/lib/CodeGen/TailDuplication.cpp (original)
> +++ llvm/trunk/lib/CodeGen/TailDuplication.cpp Thu Jun  9 16:43:25 2011
> @@ -541,13 +541,13 @@
> 
>     MachineBasicBlock *PredTBB, *PredFBB;
>     SmallVector<MachineOperand, 4> PredCond;
> +    // EH edges are ignored by AnalyzeBranch.
> +    if (PredBB->succ_size() != 1)
> +      continue;
>     if (TII->AnalyzeBranch(*PredBB, PredTBB, PredFBB, PredCond, true))
>       continue;
>     if (!PredCond.empty())
>       continue;
> -    // EH edges are ignored by AnalyzeBranch.
> -    if (PredBB->succ_size() != 1)
> -      continue;
>     // Don't duplicate into a fall-through predecessor (at least for now).
>     if (PredBB->isLayoutSuccessor(TailBB) && PredBB->canFallThrough())
>       continue;

This is fine, but I think you can remove that check altogether.  Just a few lines above, we have:

    assert(TailBB != PredBB &&
           "Single-block loop should have been rejected earlier!");
    if (PredBB->succ_size() > 1) continue;