#14769: The RecompBecause [TH] check is not resume-build-safe -------------------------------------+------------------------------------- Reporter: nh2 | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.2 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Incorrect result | Unknown/Multiple at runtime | Test Case: Blocked By: | Blocking: Related Tickets: #481 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by nh2):
we don't have the information we really need, which is "did the object file change". Perhaps we just need to be more clever and store hashes of object files as dependencies when we're using TH
@simonmar Exactly. I thought the same, and implemented that a couple days ago as a work-in-progress: https://github.com/ghc/ghc/compare/ghc-8.2.1-release...nh2:ghc-8.2.1 -release-nonrecursive-recompBecause-TH?expand=1 Would be nice if you could have a look, I can then work towards finishing that. In my preliminary experiments, this reduced the occurrance of the `[TH]` reason from 40 modules to 8 in a 150-module project. However, the big problem is still #12935, non-deterministic `.o` files. If they are nondeterministic, they will destroy object file hashing based recompilation avoidance. However, once it works, I think it will be great: With `-O0` I get (nondeterministically) a reduction from 40 modules to 1 module + relink. So I took a shot at that problem as well (making object files deterministic), taking a different approach than what was taken so far (instead of making uniques not appear in outputs, I'm trying to genrate them deterministically). In my small example it works up to a single difference in the final binary, but more work is needed. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14769#comment:2 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler