[llvm] r290786 - [ValueTracking] make dominator tree requirement explicit for isKnownNonNullFromDominatingCondition(); NFCI

[Davide Italiano via llvm-commits]

On Sat, Dec 31, 2016 at 9:37 AM, Sanjay Patel via llvm-commits
<llvm-commits at lists.llvm.org> wrote:
> Author: spatel
> Date: Sat Dec 31 11:37:01 2016
> New Revision: 290786
>
> URL: http://llvm.org/viewvc/llvm-project?rev=290786&view=rev
> Log:
> [ValueTracking] make dominator tree requirement explicit for isKnownNonNullFromDominatingCondition(); NFCI
>
> I don't think this hole is currently exposed, but I crashed regression tests for
> jump-threading and loop-vectorize after I added calls to isKnownNonNullAt() in
> InstSimplify as part of trying to solve PR28430:
> https://llvm.org/bugs/show_bug.cgi?id=28430
>
> That's because they call into value tracking with a context instruction, but no
> other parts of the query structure filled in.
>
> For more background, see the discussion in:
> https://reviews.llvm.org/D27855
>
> Modified:
>     llvm/trunk/include/llvm/Analysis/ValueTracking.h
>     llvm/trunk/lib/Analysis/ValueTracking.cpp
>
> Modified: llvm/trunk/include/llvm/Analysis/ValueTracking.h
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/Analysis/ValueTracking.h?rev=290786&r1=290785&r2=290786&view=diff
> ==============================================================================
> --- llvm/trunk/include/llvm/Analysis/ValueTracking.h (original)
> +++ llvm/trunk/include/llvm/Analysis/ValueTracking.h Sat Dec 31 11:37:01 2016
> @@ -308,12 +308,12 @@ template <typename T> class ArrayRef;
>    bool isKnownNonNull(const Value *V);
>
>    /// Return true if this pointer couldn't possibly be null. If the context
> -  /// instruction is specified, perform context-sensitive analysis and return
> -  /// true if the pointer couldn't possibly be null at the specified
> -  /// instruction.
> +  /// instruction and dominator tree are specified, perform context-sensitive
> +  /// analysis and return true if the pointer couldn't possibly be null at the
> +  /// specified instruction.
>    bool isKnownNonNullAt(const Value *V,
>                          const Instruction *CtxI = nullptr,
> -                        const DominatorTree *DT  = nullptr);
> +                        const DominatorTree *DT = nullptr);
>
>    /// Return true if it is valid to use the assumptions provided by an
>    /// assume intrinsic, I, at the point in the control-flow identified by the
>
> Modified: llvm/trunk/lib/Analysis/ValueTracking.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/ValueTracking.cpp?rev=290786&r1=290785&r2=290786&view=diff
> ==============================================================================
> --- llvm/trunk/lib/Analysis/ValueTracking.cpp (original)
> +++ llvm/trunk/lib/Analysis/ValueTracking.cpp Sat Dec 31 11:37:01 2016
> @@ -3368,6 +3368,8 @@ static bool isKnownNonNullFromDominating
>                                                    const DominatorTree *DT) {
>    assert(V->getType()->isPointerTy() && "V must be pointer type");
>    assert(!isa<ConstantData>(V) && "Did not expect ConstantPointerNull");
> +  assert(CtxI && "Context instruction required for analysis");
> +  assert(DT && "Dominator tree required for analysis");
>
>    unsigned NumUsesExplored = 0;
>    for (auto *U : V->users()) {
> @@ -3410,7 +3412,10 @@ bool llvm::isKnownNonNullAt(const Value
>    if (isKnownNonNull(V))
>      return true;
>
> -  return CtxI ? ::isKnownNonNullFromDominatingCondition(V, CtxI, DT) : false;
> +  if (!CtxI || !DT)
> +    return false;
> +

How hard is to guarantee that we always have a valid/updated dominator
when we get here (i.e. we don't need to bail out)?

-- 
Davide

"There are no solved problems; there are only problems that are more
or less solved" -- Henri Poincare