#13589: Possible inconsistency in CSE's treatment of NOINLINE -------------------------------------+------------------------------------- Reporter: bgamari | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- While debugging #13535 I noticed the following inconsistency in CSE: `Note [CSE for INLINE and NOINLINE]` states that we need to take care when adding expressions bound to binders with inline pragmas to the `CSEnv`. To see why, consider the following, {{{#!hs {-# NOINLINE bar #-} bar = <rhs> -- Same rhs as foo foo = <rhs> }}} Given this program, we need to avoid producing `foo = bar` since doing so would mean that we would lose the ability to inline `foo`'s original RHS. The note then goes on to give the following rule,
We should not add
{{{<rhs> :-> bar}}}
to the CSEnv if `bar` has any constraints on when it can inline; that is, if its 'activation' not always active. Otherwise we might replace `<rhs>` by `bar`, and then later be unable to see that it really was `<rhs>`. This rule is implemented in `noCSE` with, {{{#!hs not (isAlwaysActive (idInlineActivation id)) }}}
However, it's quite unclear to me that this rule avoids the issue we set out to solve. Afterall, `NOINLINE bar` is always active, but it still means that rewriting `foo` to `foo=bar` would lose us the ability to see `foo`'s original RHS. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13589 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler