[PATCH] D43242: [Coroutines] PR34897: Fix incorrect elisions

[Brian Gesiak via Phabricator via llvm-commits]

modocache created this revision.
modocache added reviewers: rsmith, GorNishanov, eric_niebler.
Herald added a subscriber: EricWF.

https://bugs.llvm.org/show_bug.cgi?id=34897 demonstrates an incorrect
coroutine frame allocation elision in the coro-elide pass. The elision
is performed on the basis that the SSA variables from all llvm.coro.begin
are directly referenced in subsequent llvm.coro.destroy instructions.

However, this ignores the fact that the function may exit through paths
that do not run these destroy instructions. In the sample program from
PR34897, for example, the llvm.coro.destroy instruction is only
executed in exception handling code. When the coroutine function exits
normally, llvm.coro.destroy is not called. Eliding the allocation in
this case causes a subsequent reference to the coroutine handle from
outside of the function to access freed memory.

To fix the issue, only elide allocations if the set of llvm.coro.destroy
instructions dominate all reachable terminator instructions in the function.

Test Plan:

1. Download the sample program from https://bugs.llvm.org/show_bug.cgi?id=34897, compile it with `clang++ -fcoroutines-ts -stdlib=libc++ -std=c++1z -O2`, and run it. It should print `"run1\ncheck1\nrun2\ncheck2"` and then exit successfully.
2. `check-llvm`


Repository:
  rL LLVM

https://reviews.llvm.org/D43242

Files:
  lib/Transforms/Coroutines/CoroElide.cpp
  test/Transforms/Coroutines/coro-heap-elide.ll

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