[GHC] #8903: Add dead store elimination
#8903: Add dead store elimination ------------------------------------+------------------------------------- Reporter: tibbe | Owner: Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.9 Keywords: | Operating System: Unknown/Multiple Architecture: Unknown/Multiple | Type of failure: None/Unknown Difficulty: Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | ------------------------------------+------------------------------------- We could use some dead store elimination in the code generator. Here's some Cmm that has redundant stores to the same locations: {{{ // thawArray#: I64[Hp - 168] = I64[PicBaseReg + stg_MUT_ARR_PTRS_DIRTY_info@GOTPCREL]; I64[Hp - 160] = 16; I64[Hp - 152] = 17; _c2nT::I64 = Hp - 168; call MO_Memcpy(_c2nT::I64 + 24, _s2cx::P64 + 24, 128, 8); // writeArray#: P64[(_c2nT::I64 + 24) + (_s2cy::I64 << 3)] = _s2cE::P64; I64[_c2nT::I64] = I64[PicBaseReg + stg_MUT_ARR_PTRS_DIRTY_info@GOTPCREL]; I8[(_c2nT::I64 + 24) + ((I64[_c2nT::I64 + 8] << 3) + (_s2cy::I64 >> 7))] = 1 :: W8; // unsafeFreeze# I64[_c2nT::I64] = I64[PicBaseReg + stg_MUT_ARR_PTRS_FROZEN0_info@GOTPCREL]; }}} There are three stores to the same location (`I64[_c2nT::I64]`). (There's also one much less obvious double store to another location, which will probably be much harder to address: the store to `P64[(_c2nT::I64 + 24) + (_s2cy::I64 << 3)]` overwrites a word previous written by the `MO_Memcpy`. Getting to that one will be hard as the memcoy callish !MachOp only gets expanded in the backend.) -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8903 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#8903: Add dead store elimination -------------------------------------+------------------------------------- Reporter: tibbe | Owner: (none) Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.9 Resolution: | Keywords: 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: | -------------------------------------+------------------------------------- -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8903#comment:2 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#8903: Add dead store elimination -------------------------------------+------------------------------------- Reporter: tibbe | Owner: (none) Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.9 Resolution: | Keywords: CodeGen 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: | -------------------------------------+------------------------------------- Changes (by simonpj): * keywords: => CodeGen -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8903#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#8903: Add dead store elimination -------------------------------------+------------------------------------- Reporter: tibbe | Owner: (none) Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.9 Resolution: | Keywords: CodeGen 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 srb): Im willing to take this on, although I still haven't fully wrapped my head around Hoopl. If it's OK for me to have a go, I would appreciate it if I could have some advice on a few issues: 1) This proposed analysis seems quite similar to what's being done in CmmLive/CmmSink. Would it be a good idea to attempt to incorporate it into those passes? 2) The liveness analysis is also used for inlining assignments which are used once, propagating constants, and pushing down assigments. Is it a good idea to do the same thing with stores? Thanks, Sean -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8903#comment:4 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#8903: Add dead store elimination -------------------------------------+------------------------------------- Reporter: tibbe | Owner: (none) Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.9 Resolution: | Keywords: CodeGen 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: | -------------------------------------+------------------------------------- Changes (by simonpj): * cc: email@…, michal.terepeta@…, kavon@… (added) Comment: cc'ing folk interested in Hoopl, who may be able to help. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8903#comment:5 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
participants (1)
-
GHC