#8275: Loopification breaks profiling ----------------------------------------+---------------------------------- Reporter: jstolarek | Owner: Type: bug | Status: patch Priority: high | Milestone: 7.8.1 Component: Profiling | Version: 7.7 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Building GHC failed | Unknown/Multiple Test Case: | Difficulty: Unknown Blocking: | Blocked By: 8456 | Related Tickets: ----------------------------------------+---------------------------------- Changes (by parcs): * status: new => patch Comment: I have attached a patch that fixes loopification with profiling. The problem is that `nodeReg` aka R1 may get clobbered inside the body of a closure. With profiling, upon entering a closure, `enterFunCCS` is called with R1 passed to it. But since R1 may get clobbered inside the body of a closure, and since a self-recursive tail call does not restore R1, a subsequent call to `enterFunCCS` may be passed a bogus value from R1. The solution is to not pass `nodeReg` aka R1 to `enterFunCCS`. Instead, we pass `node`, the callee-saved temporary that stores the original value of R1. This way R1 may get clobbered and loopification will not care. I don't know whether it's necessary to re-run the LDV code after looping. Not doing so certainly does not cause a segfault, anyway. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8275#comment:32 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler