[llvm] r258273 - [Inliner/WinEH] Honor implicit nounwinds

[David Majnemer via llvm-commits]

Yes, it's good to merge.

On Wed, Jan 20, 2016 at 9:42 AM, Hans Wennborg <hans at chromium.org> wrote:

> David, is this OK for 3.8? The PR is marked as a potential release blocker.
>
> On Tue, Jan 19, 2016 at 6:15 PM, Joseph Tremoulet via llvm-commits
> <llvm-commits at lists.llvm.org> wrote:
> > Author: josepht
> > Date: Tue Jan 19 20:15:15 2016
> > New Revision: 258273
> >
> > URL: http://llvm.org/viewvc/llvm-project?rev=258273&view=rev
> > Log:
> > [Inliner/WinEH] Honor implicit nounwinds
> >
> > Summary:
> > Funclet EH tables require that a given funclet have only one unwind
> > destination for exceptional exits.  The verifier will therefore reject
> > e.g. two cleanuprets with different unwind dests for the same cleanup, or
> > two invokes exiting the same funclet but to different unwind dests.
> > Because catchswitch has no 'nounwind' variant, and because IR producers
> > are not *required* to annotate calls which will not unwind as 'nounwind',
> > it is legal to nest a call or an "unwind to caller" catchswitch within a
> > funclet pad that has an unwind destination other than caller; it is
> > undefined behavior for such a call or catchswitch to unwind.
> >
> > Normally when inlining an invoke, calls in the inlined sequence are
> > rewritten to invokes that unwind to the callsite invoke's unwind
> > destination, and "unwind to caller" catchswitches in the inlined sequence
> > are rewritten to unwind to the callsite invoke's unwind destination.
> > However, if such a call or "unwind to caller" catchswitch is located in a
> > callee funclet that has another exceptional exit with an unwind
> > destination within the callee, applying the normal transformation would
> > give that callee funclet multiple unwind destinations for its exceptional
> > exits.  There would be no way for EH table generation to determine which
> > is the "true" exit, and the verifier would reject the function
> > accordingly.
> >
> > Add logic to the inliner to detect these cases and leave such calls and
> > "unwind to caller" catchswitches as calls and "unwind to caller"
> > catchswitches in the inlined sequence.
> >
> > This fixes PR26147.
> >
> >
> > Reviewers: rnk, andrew.w.kaylor, majnemer
> >
> > Subscribers: alexcrichton, llvm-commits
> >
> > Differential Revision: http://reviews.llvm.org/D16319
>
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