#14211: Compiler is unable to INLINE as well as the programmer can manually -------------------------------------+------------------------------------- Reporter: harendra | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.1 Resolution: | Keywords: | StaticArgumentTransformation, | Inlining Operating System: Unknown/Multiple | Architecture: Type of failure: Runtime | Unknown/Multiple performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by harendra): That information is a gem for optimization! I need to change how I code recursive functions. Every programmer must know that a static argument impacts performance significantly and can be easily optimized. It not only recovered the lost performance but gave a lot more because the manually inlined bind function also has a static argument which got removed in this version. I think the problem is not really inlining. GHC won't be able to inline the recursive call of a function to itself, of course, but it can still inline the whole function. So `bindWith` is likely getting inlined, I can see that with `-ddump-inlinings`. I guess, the problem is that we have added one more static argument which degrades the performance. The compiler is able to inline the function but it cannot undo that static argument. I see that the INLINE section in the GHC manual mentions mutually recursive and recursive functions, however it does not mention `-fstatic- argument-transformation`. It may be useful to mention because the programmer naively expects that inlining will give us equivalent code but in reality the added static argument is an overhead that cannot be reverted by the compiler. I have a few questions, suggestions: 1) The INLINE section of the manual should mention `-fstatic-argument- transformation` and how factoring out of code can add a static argument that cannot be undone by the compiler unless we use this option. Also, an example of how the programmer can manually perform static argument transformation and achieve what (s)he wants in case this option does not work. 2) Can we have a warning option which warns the programmer about missed inlining? If I have placed an INLINE pragma and the compiler is unable to inline the function for whatever reason I want to know. The `-ddump- inlinings` shows what got inlined but what did not get inlined will be more useful information. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14211#comment:2 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler