#7297: LLVM incorrectly hoisting loads
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Reporter: dterei | Owner: dterei
Type: bug | Status: new
Priority: normal | Component: Compiler (LLVM)
Version: 7.7 | Keywords:
Os: Unknown/Multiple | Architecture: Unknown/Multiple
Failure: Incorrect result at runtime | Testcase: 367_letnoescape
Blockedby: | Blocking:
Related: |
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test 367_letnoescape fails under LLVM as a load of the HpLim register is
hoisted out of the loop. So yielding is never done.
What I am not sure about right now is the best way to fix. Loads in LLVM
can be annotated in a few different ways to fix this and not sure which
one is the most 'correct'.
All the following work:
* mark the load as volatile. (seems to give nicest code as well)
* mark the load as atomic with either monotonic or seq_cst ordering.
* mark the load as both volatile and atomic.
This bug while only affecting a single test case seems very serious and
potentially indicative of a large problem. How well are we communicating
the load/store threaded semantics to LLVM?
So making a bug for now as I don't know yet the best way to proceed
without dedicating some time to reading LLVM docs and probably talking to
the LLVM devs as the docs on the memory model are fairly confusing.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7297>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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