[PATCH] D71663: [Coroutines] CoroElide enhancement

[JunMa via Phabricator via llvm-commits]

junparser created this revision.
junparser added reviewers: GorNishanov, modocache.
Herald added subscribers: llvm-commits, hiraditya, EricWF.
Herald added a project: LLVM.
junparser edited the summary of this revision.

According to https://reviews.llvm.org/D43242,  coroelide pass only considers llvm.coro.destroy that dominate non-exceptional return. However,  this cannot be met if current function is coroutine function because of suspend point.
Consider case from  http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p0978r0.html :

  task<> big_task() { // lifetime of `subtask` is fully enclosed in its caller
    co_await subtask(); // coroutine frame allocation elided 
  }

such cases should be optimized.

this patch does two changes in shouldElide function:

1. Consider final coro.suspend as real  non-exceptional terminator when function is coroutine, since final suspend is executed with or without  exception at last.
2. When function body is wrapped by try-catch, block of coro.suspend may has multiple predecessors : one normal path and the others are exceptional path,  and they do not dominate each other.  If all the predecessors dominate coro.destroys that reference same coro.begin,  we consider condition is met.
3. Keep normal function as usual

Test Plan:
Compile https://godbolt.org/g/mCKfnr and confirm it is still optimized to a single instruction, 'return 1190'.
Compile and run https://godbolt.org/z/AbdRw4, there is no "new" and "delete" output
Compile and run https://godbolt.org/z/gjYSi5 , there is no "new" and "delete" output
check-llvm


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D71663

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

-------------- next part --------------
A non-text attachment was scrubbed...
Name: D71663.234526.patch
Type: text/x-patch
Size: 9645 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20191218/dece16f5/attachment.bin>