[llvm] r183459 - CodeGenSchedule: smallvector.push_back(smallvector[0]) is dangerous

[David Blaikie]

On Thu, Jun 6, 2013 at 4:23 PM, Arnold Schwaighofer
<aschwaighofer at apple.com> wrote:
> Author: arnolds
> Date: Thu Jun  6 18:23:14 2013
> New Revision: 183459
>
> URL: http://llvm.org/viewvc/llvm-project?rev=183459&view=rev
> Log:
> CodeGenSchedule: smallvector.push_back(smallvector[0]) is dangerous
>
> The element passed to push_back is not copied before the vector reallocates.

A similar change to this has been previously reverted: r178319

We should probably fix SmallVector to allow this, consistent with
standard containers, to avoid this pitfall now & in the future.

> The client needs to copy the element first before passing it to push_back.
>
> No test case, will be tested by follow-up swift scheduler model change (it
> segfaults without this change).
>
> Modified:
>     llvm/trunk/utils/TableGen/CodeGenSchedule.cpp
>
> Modified: llvm/trunk/utils/TableGen/CodeGenSchedule.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/utils/TableGen/CodeGenSchedule.cpp?rev=183459&r1=183458&r2=183459&view=diff
> ==============================================================================
> --- llvm/trunk/utils/TableGen/CodeGenSchedule.cpp (original)
> +++ llvm/trunk/utils/TableGen/CodeGenSchedule.cpp Thu Jun  6 18:23:14 2013
> @@ -1172,7 +1172,9 @@ pushVariant(const TransVariant &VInfo, b
>      unsigned OperIdx = RWSequences.size()-1;
>      // Make N-1 copies of this transition's last sequence.
>      for (unsigned i = 1, e = SelectedRWs.size(); i != e; ++i) {
> -      RWSequences.push_back(RWSequences[OperIdx]);
> +      // Create a temporary copy the vector could reallocate.
> +      SmallVector<unsigned, 4> Tmp = RWSequences[OperIdx];
> +      RWSequences.push_back(Tmp);
>      }
>      // Push each of the N elements of the SelectedRWs onto a copy of the last
>      // sequence (split the current operand into N operands).
>
>
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