[llvm] 18eae33 - [SCEV] Fix usage of invalid IP with FoldingSet

[Roman Lebedev via llvm-commits]

This actually reaffirms my point - was there test covering this?
If not, it might be good to add one.

On Fri, Mar 13, 2020 at 7:45 PM Ehud Katz <ehudkatz at gmail.com> wrote:
>
> This is actually to fix a regression caused by rGfcc2238b8bfb9498b46a48d219193de8c00a25a0.
> These lines of code actually existed before the change, but removed incorrectly.
>
> On Fri, Mar 13, 2020 at 6:38 PM Roman Lebedev <lebedev.ri at gmail.com> wrote:
>>
>> Any chance for a test for this?
>>
>> On Fri, Mar 13, 2020 at 7:37 PM Ehud Katz via llvm-commits
>> <llvm-commits at lists.llvm.org> wrote:
>> >
>> >
>> > Author: Ehud Katz
>> > Date: 2020-03-13T18:36:58+02:00
>> > New Revision: 18eae3312297cb197a3131f3ad9ca2bebb217415
>> >
>> > URL: https://github.com/llvm/llvm-project/commit/18eae3312297cb197a3131f3ad9ca2bebb217415
>> > DIFF: https://github.com/llvm/llvm-project/commit/18eae3312297cb197a3131f3ad9ca2bebb217415.diff
>> >
>> > LOG: [SCEV] Fix usage of invalid IP with FoldingSet
>> >
>> > Fix the use of invalid Insertion Point pointer with the UniqueSCEVs FoldingSet,
>> > which caused memory corruption.
>> >
>> > Added:
>> >
>> >
>> > Modified:
>> >     llvm/lib/Analysis/ScalarEvolution.cpp
>> >
>> > Removed:
>> >
>> >
>> >
>> > ################################################################################
>> > diff  --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp
>> > index debd03bf47b8..030de8cf90b7 100644
>> > --- a/llvm/lib/Analysis/ScalarEvolution.cpp
>> > +++ b/llvm/lib/Analysis/ScalarEvolution.cpp
>> > @@ -3339,6 +3339,10 @@ const SCEV *ScalarEvolution::getUDivExpr(const SCEV *LHS,
>> >      }
>> >    }
>> >
>> > +  // The Insertion Point (IP) might be invalid by now (due to UniqueSCEVs
>> > +  // changes). Make sure we get a new one.
>> > +  IP = nullptr;
>> > +  if (const SCEV *S = UniqueSCEVs.FindNodeOrInsertPos(ID, IP)) return S;
>> >    SCEV *S = new (SCEVAllocator) SCEVUDivExpr(ID.Intern(SCEVAllocator),
>> >                                               LHS, RHS);
>> >    UniqueSCEVs.InsertNode(S, IP);
>> >
>> >
>> >
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