[llvm] r257279 - [JumpThreading] Don't forget to report that the IR changed

[David Blaikie via llvm-commits]

any way to test this?

On Sat, Jan 9, 2016 at 11:13 PM, David Majnemer via llvm-commits <
llvm-commits at lists.llvm.org> wrote:

> Author: majnemer
> Date: Sun Jan 10 01:13:04 2016
> New Revision: 257279
>
> URL: http://llvm.org/viewvc/llvm-project?rev=257279&view=rev
> Log:
> [JumpThreading] Don't forget to report that the IR changed
>
> JumpThreading's runOnFunction is supposed to return true if it made any
> changes.  JumpThreading has a call to removeUnreachableBlocks which may
> result in changes to the IR but runOnFunction didn't appropriate account
> for this possibility, leading to badness.
>
> While we are here, make sure to call LazyValueInfo::eraseBlock in
> removeUnreachableBlocks;  JumpThreading preserves LVI.
>
> This fixes PR26096.
>
> Modified:
>     llvm/trunk/include/llvm/Transforms/Utils/Local.h
>     llvm/trunk/lib/Transforms/Scalar/JumpThreading.cpp
>     llvm/trunk/lib/Transforms/Utils/Local.cpp
>
> Modified: llvm/trunk/include/llvm/Transforms/Utils/Local.h
> URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/Transforms/Utils/Local.h?rev=257279&r1=257278&r2=257279&view=diff
>
> ==============================================================================
> --- llvm/trunk/include/llvm/Transforms/Utils/Local.h (original)
> +++ llvm/trunk/include/llvm/Transforms/Utils/Local.h Sun Jan 10 01:13:04
> 2016
> @@ -42,6 +42,7 @@ class TargetLibraryInfo;
>  class TargetTransformInfo;
>  class DIBuilder;
>  class DominatorTree;
> +class LazyValueInfo;
>
>  template<typename T> class SmallVectorImpl;
>
> @@ -303,7 +304,7 @@ void removeUnwindEdge(BasicBlock *BB);
>  /// \brief Remove all blocks that can not be reached from the function's
> entry.
>  ///
>  /// Returns true if any basic block was removed.
> -bool removeUnreachableBlocks(Function &F);
> +bool removeUnreachableBlocks(Function &F, LazyValueInfo *LVI = nullptr);
>
>  /// \brief Combine the metadata of two instructions so that K can replace
> J
>  ///
>
> Modified: llvm/trunk/lib/Transforms/Scalar/JumpThreading.cpp
> URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/JumpThreading.cpp?rev=257279&r1=257278&r2=257279&view=diff
>
> ==============================================================================
> --- llvm/trunk/lib/Transforms/Scalar/JumpThreading.cpp (original)
> +++ llvm/trunk/lib/Transforms/Scalar/JumpThreading.cpp Sun Jan 10 01:13:04
> 2016
> @@ -211,11 +211,12 @@ bool JumpThreading::runOnFunction(Functi
>    // we will loop forever. We take care of this issue by not jump
> threading for
>    // back edges. This works for normal cases but not for unreachable
> blocks as
>    // they may have cycle with no back edge.
> -  removeUnreachableBlocks(F);
> +  bool EverChanged = false;
> +  EverChanged |= removeUnreachableBlocks(F, LVI);
>
>    FindLoopHeaders(F);
>
> -  bool Changed, EverChanged = false;
> +  bool Changed;
>    do {
>      Changed = false;
>      for (Function::iterator I = F.begin(), E = F.end(); I != E;) {
>
> Modified: llvm/trunk/lib/Transforms/Utils/Local.cpp
> URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Utils/Local.cpp?rev=257279&r1=257278&r2=257279&view=diff
>
> ==============================================================================
> --- llvm/trunk/lib/Transforms/Utils/Local.cpp (original)
> +++ llvm/trunk/lib/Transforms/Utils/Local.cpp Sun Jan 10 01:13:04 2016
> @@ -23,6 +23,7 @@
>  #include "llvm/Analysis/EHPersonalities.h"
>  #include "llvm/Analysis/InstructionSimplify.h"
>  #include "llvm/Analysis/MemoryBuiltins.h"
> +#include "llvm/Analysis/LazyValueInfo.h"
>  #include "llvm/Analysis/ValueTracking.h"
>  #include "llvm/IR/CFG.h"
>  #include "llvm/IR/Constants.h"
> @@ -1407,7 +1408,7 @@ void llvm::removeUnwindEdge(BasicBlock *
>  /// removeUnreachableBlocksFromFn - Remove blocks that are not reachable,
> even
>  /// if they are in a dead cycle.  Return true if a change was made, false
>  /// otherwise.
> -bool llvm::removeUnreachableBlocks(Function &F) {
> +bool llvm::removeUnreachableBlocks(Function &F, LazyValueInfo *LVI) {
>    SmallPtrSet<BasicBlock*, 128> Reachable;
>    bool Changed = markAliveBlocks(F, Reachable);
>
> @@ -1428,6 +1429,8 @@ bool llvm::removeUnreachableBlocks(Funct
>           ++SI)
>        if (Reachable.count(*SI))
>          (*SI)->removePredecessor(&*BB);
> +    if (LVI)
> +      LVI->eraseBlock(&*BB);
>      BB->dropAllReferences();
>    }
>
>
>
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