[llvm] r329865 - Reapply "[PR16756] Use SSAUpdaterBulk in JumpThreading." one more time.

[Benjamin Kramer via llvm-commits]

I'm still seeing stage2/3 miscompares of clang during bootstrap with this.
Reverted in r329910.

On Thu, Apr 12, 2018 at 12:40 AM Michael Zolotukhin via llvm-commits <
llvm-commits at lists.llvm.org> wrote:

> Author: mzolotukhin
> Date: Wed Apr 11 16:37:53 2018
> New Revision: 329865
>
> URL: http://llvm.org/viewvc/llvm-project?rev=329865&view=rev
> Log:
> Reapply "[PR16756] Use SSAUpdaterBulk in JumpThreading." one more time.
>
> This reapplies commit r329644.
>
> Modified:
>     llvm/trunk/lib/Transforms/Scalar/JumpThreading.cpp
>
> Modified: llvm/trunk/lib/Transforms/Scalar/JumpThreading.cpp
> URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/JumpThreading.cpp?rev=329865&r1=329864&r2=329865&view=diff
>
> ==============================================================================
> --- llvm/trunk/lib/Transforms/Scalar/JumpThreading.cpp (original)
> +++ llvm/trunk/lib/Transforms/Scalar/JumpThreading.cpp Wed Apr 11 16:37:53
> 2018
> @@ -66,6 +66,7 @@
>  #include "llvm/Transforms/Utils/BasicBlockUtils.h"
>  #include "llvm/Transforms/Utils/Cloning.h"
>  #include "llvm/Transforms/Utils/SSAUpdater.h"
> +#include "llvm/Transforms/Utils/SSAUpdaterBulk.h"
>  #include "llvm/Transforms/Utils/ValueMapper.h"
>  #include <algorithm>
>  #include <cassert>
> @@ -1989,9 +1990,13 @@ bool JumpThreadingPass::ThreadEdge(Basic
>    // now have to update all uses of the value to use either the original
> value,
>    // the cloned value, or some PHI derived value.  This can require
> arbitrary
>    // PHI insertion, of which we are prepared to do, clean these up now.
> -  SSAUpdater SSAUpdate;
> +  SSAUpdaterBulk SSAUpdate;
>    SmallVector<Use*, 16> UsesToRename;
> +
> +  unsigned VarNum = 0;
>    for (Instruction &I : *BB) {
> +    UsesToRename.clear();
> +
>      // Scan all uses of this instruction to see if it is used outside of
> its
>      // block, and if so, record them in UsesToRename.
>      for (Use &U : I.uses()) {
> @@ -2008,19 +2013,15 @@ bool JumpThreadingPass::ThreadEdge(Basic
>      // If there are no uses outside the block, we're done with this
> instruction.
>      if (UsesToRename.empty())
>        continue;
> +    SSAUpdate.AddVariable(VarNum, I.getName(), I.getType());
>
> -    DEBUG(dbgs() << "JT: Renaming non-local uses of: " << I << "\n");
> -
> -    // We found a use of I outside of BB.  Rename all uses of I that are
> outside
> -    // its block to be uses of the appropriate PHI node etc.  See
> ValuesInBlocks
> -    // with the two values we know.
> -    SSAUpdate.Initialize(I.getType(), I.getName());
> -    SSAUpdate.AddAvailableValue(BB, &I);
> -    SSAUpdate.AddAvailableValue(NewBB, ValueMapping[&I]);
> -
> -    while (!UsesToRename.empty())
> -      SSAUpdate.RewriteUse(*UsesToRename.pop_back_val());
> -    DEBUG(dbgs() << "\n");
> +    // We found a use of I outside of BB - we need to rename all uses of
> I that
> +    // are outside its block to be uses of the appropriate PHI node etc.
> +    SSAUpdate.AddAvailableValue(VarNum, BB, &I);
> +    SSAUpdate.AddAvailableValue(VarNum, NewBB, ValueMapping[&I]);
> +    for (auto U : UsesToRename)
> +      SSAUpdate.AddUse(VarNum, U);
> +    VarNum++;
>    }
>
>    // Ok, NewBB is good to go.  Update the terminator of PredBB to jump to
> @@ -2037,6 +2038,10 @@ bool JumpThreadingPass::ThreadEdge(Basic
>                       {DominatorTree::Insert, PredBB, NewBB},
>                       {DominatorTree::Delete, PredBB, BB}});
>
> +  // Apply all updates we queued with DDT and get the updated Dominator
> Tree.
> +  DominatorTree *DT = &DDT->flush();
> +  SSAUpdate.RewriteAllUses(DT);
> +
>    // At this point, the IR is fully up to date and consistent.  Do a
> quick scan
>    // over the new instructions and zap any that are constants or dead.
> This
>    // frequently happens because of phi translation.
>
>
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