#11295: Figure out what LLVM passes are fruitful -------------------------------------+------------------------------------- Reporter: bgamari | Owner: bgamari Type: task | Status: new Priority: normal | Milestone: Component: Compiler (LLVM) | Version: 7.10.3 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Description changed by bgamari: Old description:

Builds using GHC's LLVM backend are currently substantially slower than GHC's own native code generator. There are a few possible reasons for this,

1. the cost of forking processes and serializing/parsing LLVM's intermediate representation 2. the cost of the more powerful optimizations responsible for LLVM's (hopefully) better code generation 3. the cost of redundant optimizations overlapping effort already expended by GHC

Given that some architecture (e.g. ARM) are only supported by LLVM and therefore suffer considerably at the hand of our slow builds, we should try to reduce #

New description: Builds using GHC's LLVM backend are currently substantially slower than GHC's own native code generator. There are a few possible reasons for this, 1. the cost of forking processes and serializing/parsing LLVM's intermediate representation 2. the cost of the more powerful optimizations responsible for LLVM's (hopefully) better code generation 3. the cost of redundant optimizations overlapping effort already expended by GHC Given that some architecture (e.g. ARM) are only supported by LLVM and therefore suffer considerably at the hand of our slow builds, we should try to reduce #3. -- -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11295#comment:2 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#11295: Figure out what LLVM passes are fruitful -------------------------------------+------------------------------------- Reporter: bgamari | Owner: bgamari Type: task | Status: new Priority: normal | Milestone: Component: Compiler (LLVM) | Version: 7.10.3 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by angerman): * cc: angerman (added) -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11295#comment:4 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#11295: Figure out what LLVM passes are fruitful -------------------------------------+------------------------------------- Reporter: bgamari | Owner: Type: task | Status: new Priority: normal | Milestone: Component: Compiler (LLVM) | Version: 7.10.3 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by michalt): * cc: michalt (added) -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11295#comment:6 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#11295: Figure out what LLVM passes are fruitful -------------------------------------+------------------------------------- Reporter: bgamari | Owner: (none) Type: task | Status: new Priority: normal | Milestone: Component: Compiler (LLVM) | Version: 7.10.3 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by bgamari): One useful tool for this may be [[http://opentuner.org/publications/|OpenTuner]], which is mentioned in [[https://www.youtube.com/watch?v=P3eJwoD97bY|this talk]] in the context of tuning optimization pass sequences. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11295#comment:8 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#11295: Figure out what LLVM passes are fruitful -------------------------------------+------------------------------------- Reporter: bgamari | Owner: kavon Type: task | Status: new Priority: normal | Milestone: Component: Compiler (LLVM) | Version: 7.10.3 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by kavon): Actually I'm now using OpenTune, repo with the bootstrap code forthcoming. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11295#comment:10 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#11295: Figure out what LLVM passes are fruitful -------------------------------------+------------------------------------- Reporter: bgamari | Owner: kavon Type: task | Status: new Priority: normal | Milestone: Component: Compiler (LLVM) | Version: 7.10.3 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by bgamari): Yay! Thanks kavon. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11295#comment:12 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#11295: Figure out what LLVM passes are fruitful -------------------------------------+------------------------------------- Reporter: bgamari | Owner: kavon Type: task | Status: new Priority: normal | Milestone: Component: Compiler (LLVM) | Version: 7.10.3 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by kavon): Ben, I think the autotuner is now ready to be applied to Haskell programs: it can successfully tune C/C++ programs, with or without running the output program, to match -O3 in a reasonable time. If it's not too late, I can try to get something in for 8.4. My plan is to pick a few "representative" programs*, tune on each one individually, and see which pass ordering does the best across nofib. If one of them does better than the -Ox passes, we could drop it in GHC pretty easily. What do you think? * Suggestions are welcome here. Infrastructure to tune against the "average" of several programs (using a special objective function) would be ideal, but that infrastructure is not ready yet. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11295#comment:14 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#11295: Figure out what LLVM passes are fruitful -------------------------------------+------------------------------------- Reporter: bgamari | Owner: kavon Type: task | Status: new Priority: normal | Milestone: Component: Compiler (LLVM) | Version: 7.10.3 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: 14528 | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by bgamari): kavon, any progress on this? It would be great to have something for 8.6. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11295#comment:17 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#11295: Figure out what LLVM passes are fruitful -------------------------------------+------------------------------------- Reporter: bgamari | Owner: kavon Type: task | Status: new Priority: normal | Milestone: 8.6.1 Component: Compiler (LLVM) | Version: 7.10.3 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: 14528 | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by Ben Gamari ): In [changeset:"a4ae199cf810a63444a4ef24a44b33329023cd93/ghc" a4ae199/ghc]: {{{ #!CommitTicketReference repository="ghc" revision="a4ae199cf810a63444a4ef24a44b33329023cd93" Extract hard-coded LLVM opt flags into a file To resolve ticket #11295, I think it makes sense to stop hard-coding the pass sequences used by GHC when compiling with LLVM into the compiler itself. This patchset introduces a companion to the existing `llvm-targets` file called `llvm-passes`. The passes file is a simple association list that holds the default LLVM `opt` pass sequence used by GHC. This allows end users to easily save their favorite optimization flags when compiling with LLVM. The main benefit for ticket #11295 is that when adding a custom pass sequence, it tends to be an extremely long string that would be unsightly in the code. This is essentially part 1 of 2 for ticket #11295. Test Plan: ./validate Reviewers: bgamari, angerman Reviewed By: angerman Subscribers: rwbarton, thomie, carter Differential Revision: https://phabricator.haskell.org/D4695 }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11295#comment:19 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#11295: Figure out what LLVM passes are fruitful -------------------------------------+------------------------------------- Reporter: bgamari | Owner: kavon Type: task | Status: new Priority: normal | Milestone: 8.8.1 Component: Compiler (LLVM) | Version: 7.10.3 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: 14528 | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by bgamari): kavon, it would be great to have this done for 8.8. Do let me know if there's any way I can help. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11295#comment:22 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler