1. 23 Sep, 2015 1 commit
    • Simon Marlow's avatar
      Annotate CmmBranch with an optional likely target · 939a7d63
      Simon Marlow authored
      Summary:
      This allows the code generator to give hints to later code generation
      steps about which branch is most likely to be taken.  Right now it
      is only taken into account in one place: a special case in
      CmmContFlowOpt that swapped branches over to maximise the chance of
      fallthrough, which is now disabled when there is a likelihood setting.
      
      Test Plan: validate
      
      Reviewers: austin, simonpj, bgamari, ezyang, tibbe
      
      Subscribers: thomie
      
      Differential Revision: https://phabricator.haskell.org/D1273
      939a7d63
  2. 18 May, 2015 1 commit
    • Joachim Breitner's avatar
      CmmCommonBlockElim: Improve hash function · 73f836f5
      Joachim Breitner authored
      Previously, the hash function used to cut down the number of block
      comparisons did not take local registers into account, causing far too
      many similar, but different bocks to be considered candidates for the
      (expensive!) comparision.
      
      Adding register to the hash takes CmmCommonBlockElim's share of the
      runtime of the example in #10397 from 17% to 2.5%, and eliminates all
      unwanted hash collisions.
      
      This patch also replaces the fancy trie by a plain Data.Map. It turned
      out to be not performance critical, so this simplifies the code.
      
      Differential Revision: https://phabricator.haskell.org/D896
      73f836f5
  3. 16 May, 2015 1 commit
  4. 30 Mar, 2015 1 commit
    • Joachim Breitner's avatar
      Refactor the story around switches (#10137) · de1160be
      Joachim Breitner authored
      This re-implements the code generation for case expressions at the Stg →
      Cmm level, both for data type cases as well as for integral literal
      cases. (Cases on float are still treated as before).
      
      The goal is to allow for fancier strategies in implementing them, for a
      cleaner separation of the strategy from the gritty details of Cmm, and
      to run this later than the Common Block Optimization, allowing for one
      way to attack #10124. The new module CmmSwitch contains a number of
      notes explaining this changes. For example, it creates larger
      consecutive jump tables than the previous code, if possible.
      
      nofib shows little significant overall improvement of runtime. The
      rather large wobbling comes from changes in the code block order
      (see #8082, not much we can do about it). But the decrease in code size
      alone makes this worthwhile.
      
      ```
              Program           Size    Allocs   Runtime   Elapsed  TotalMem
                  Min          -1.8%      0.0%     -6.1%     -6.1%     -2.9%
                  Max          -0.7%     +0.0%     +5.6%     +5.7%     +7.8%
       Geometric Mean          -1.4%     -0.0%     -0.3%     -0.3%     +0.0%
      ```
      
      Compilation time increases slightly:
      ```
              -1 s.d.                -----            -2.0%
              +1 s.d.                -----            +2.5%
              Average                -----            +0.3%
      ```
      
      The test case T783 regresses a lot, but it is the only one exhibiting
      any regression. The cause is the changed order of branches in an
      if-then-else tree, which makes the hoople data flow analysis traverse
      the blocks in a suboptimal order. Reverting that gets rid of this
      regression, but has a consistent, if only very small (+0.2%), negative
      effect on runtime. So I conclude that this test is an extreme outlier
      and no reason to change the code.
      
      Differential Revision: https://phabricator.haskell.org/D720
      de1160be
  5. 16 Dec, 2014 3 commits
    • Peter Wortmann's avatar
      Add unwind information to Cmm · 711a51ad
      Peter Wortmann authored
      Unwind information allows the debugger to discover more information
      about a program state, by allowing it to "reconstruct" other states of
      the program. In practice, this means that we explain to the debugger
      how to unravel stack frames, which comes down mostly to explaining how
      to find their Sp and Ip register values.
      
      * We declare yet another new constructor for CmmNode - and this time
        there's actually little choice, as unwind information can and will
        change mid-block. We don't actually make use of these capabilities,
        and back-end support would be tricky (generate new labels?), but it
        feels like the right way to do it.
      
      * Even though we only use it for Sp so far, we allow CmmUnwind to specify
        unwind information for any register. This is pretty cheap and could
        come in useful in future.
      
      * We allow full CmmExpr expressions for specifying unwind values. The
        advantage here is that we don't have to make up new syntax, and can e.g.
        use the WDS macro directly. On the other hand, the back-end will now
        have to simplify the expression until it can sensibly be converted
        into DWARF byte code - a process which might fail, yielding NCG panics.
        On the other hand, when you're writing Cmm by hand you really ought to
        know what you're doing.
      
      (From Phabricator D169)
      711a51ad
    • Peter Wortmann's avatar
      Tick scopes · 5fecd767
      Peter Wortmann authored
      This patch solves the scoping problem of CmmTick nodes: If we just put
      CmmTicks into blocks we have no idea what exactly they are meant to
      cover.  Here we introduce tick scopes, which allow us to create
      sub-scopes and merged scopes easily.
      
      Notes:
      
      * Given that the code often passes Cmm around "head-less", we have to
        make sure that its intended scope does not get lost. To keep the amount
        of passing-around to a minimum we define a CmmAGraphScoped type synonym
        here that just bundles the scope with a portion of Cmm to be assembled
        later.
      
      * We introduce new scopes at somewhat random places, aligning with
        getCode calls. This works surprisingly well, but we might have to
        add new scopes into the mix later on if we find things too be too
        coarse-grained.
      
      (From Phabricator D169)
      5fecd767
    • Peter Wortmann's avatar
      Source notes (Cmm support) · 7ceaf96f
      Peter Wortmann authored
      This patch adds CmmTick nodes to Cmm code. This is relatively
      straight-forward, but also not very useful, as many blocks will simply
      end up with no annotations whatosever.
      
      Notes:
      
      * We use this design over, say, putting ticks into the entry node of all
        blocks, as it seems to work better alongside existing optimisations.
        Now granted, the reason for this is that currently GHC's main Cmm
        optimisations seem to mainly reorganize and merge code, so this might
        change in the future.
      
      * We have the Cmm parser generate a few source notes as well. This is
        relatively easy to do - worst part is that it complicates the CmmParse
        implementation a bit.
      
      (From Phabricator D169)
      7ceaf96f
  6. 24 Jul, 2013 1 commit
    • Simon Marlow's avatar
      Fix a bug in stack layout with safe foreign calls (#8083) · c2348859
      Simon Marlow authored
      We weren't properly tracking the number of stack arguments in the
      continuation of a foreign call.  It happened to work when the
      continuation was not a join point, but when it was a join point we
      were using the wrong amount of stack fixup.
      c2348859
  7. 09 Mar, 2013 1 commit
  8. 01 Feb, 2013 1 commit
  9. 09 Jul, 2012 1 commit
  10. 05 Jul, 2012 1 commit
  11. 07 Mar, 2012 2 commits
    • Simon Marlow's avatar
      Improve common-block elimination · 99293a48
      Simon Marlow authored
      We need to compare middle nodes and expressions modulo the BlockId
      mapping too, because there are references to BlockIds in CmmStackSlot
      and CmmBlock.  This lets us catch more common blocks - in particular
      we can share the heap-check fail code between multiple case
      alternatives, which is most cool.
      99293a48
    • Simon Marlow's avatar
      Fix a bug in common block elimination · e2ee3344
      Simon Marlow authored
      When we had more than two identical blocks, we weren't eliminating all
      the duplicates properly.
      e2ee3344
  12. 17 Jan, 2012 1 commit
  13. 19 Dec, 2011 1 commit
  14. 05 Nov, 2011 1 commit
  15. 25 Aug, 2011 1 commit
  16. 24 Jan, 2011 1 commit
    • Simon Marlow's avatar
      Merge in new code generator branch. · 889c084e
      Simon Marlow authored
      This changes the new code generator to make use of the Hoopl package
      for dataflow analysis.  Hoopl is a new boot package, and is maintained
      in a separate upstream git repository (as usual, GHC has its own
      lagging darcs mirror in http://darcs.haskell.org/packages/hoopl).
      
      During this merge I squashed recent history into one patch.  I tried
      to rebase, but the history had some internal conflicts of its own
      which made rebase extremely confusing, so I gave up. The history I
      squashed was:
      
        - Update new codegen to work with latest Hoopl
        - Add some notes on new code gen to cmm-notes
        - Enable Hoopl lag package.
        - Add SPJ note to cmm-notes
        - Improve GC calls on new code generator.
      
      Work in this branch was done by:
         - Milan Straka <fox@ucw.cz>
         - John Dias <dias@cs.tufts.edu>
         - David Terei <davidterei@gmail.com>
      
      Edward Z. Yang <ezyang@mit.edu> merged in further changes from GHC HEAD
      and fixed a few bugs.
      889c084e
  17. 24 Jul, 2009 1 commit
  18. 03 Mar, 2009 1 commit
    • dias@eecs.harvard.edu's avatar
      A few bug fixes; some improvements spurred by paper writing · 31a9d048
      dias@eecs.harvard.edu authored
      Among others:
      - Fixed Stg->C-- translation of let-no-escapes -- it's important to use the
        right continuation...
      - Fixed infinite recursion in X86 backend (shortcutJump mishandled infinite loops)
      - Fixed yet another wrong calling convention -- primops take args only in vanilla regs,
        but they may return results on the stack!
      - Removed StackInfo from LGraph and Block -- now in LastCall and CmmZ
      - Updated avail-variable and liveness code
      31a9d048
  19. 17 Oct, 2008 1 commit
  20. 13 Oct, 2008 1 commit
    • dias@eecs.harvard.edu's avatar
      Big collection of patches for the new codegen branch. · e6243a81
      dias@eecs.harvard.edu authored
      o Fixed bug that emitted the copy-in code for closure entry
        in the wrong place -- at the initialization of the closure.
      o Refactored some of the closure entry code.
      o Added code to check that no LocalRegs are live-in to a procedure
         -- trip up some buggy programs earlier
      o Fixed environment bindings for thunks
         -- we weren't (re)binding the free variables in a thunk
      o Fixed a bug in proc-point splitting that dropped some updates
        to the entry block in a procedure.
      o Fixed improper calls to code that generates CmmLit's for strings
      o New invariant on cg_loc in CgIdInfo: the expression is always tagged
      o Code to load free vars on entry to a thunk was (wrongly) placed before
        the heap check.
      o Some of the StgCmm code was redundantly passing around Id's
        along with CgIdInfo's; no more.
      o Initialize the LocalReg's that point to a closure before allocating and
        initializing the closure itself -- otherwise, we have problems with
        recursive closure bindings
      o BlockEnv and BlockSet types are now abstract.
      o Update frames:
        - push arguments in Old call area
        - keep track of the return sp in the FCode monad
        - keep the return sp in every call, tail call, and return
            (because it might be different at different call sites,
             e.g. tail calls to the gc after a heap check are performed
                  before pushing the update frame)
        - set the sp appropriately on returns and tail calls
      o Reduce call, tail call, and return to a single LastCall node
      o Added slow entry code, using different calling conventions on entry and tail call
      o More fixes to the calling convention code.
        The tricky stuff is all about the closure environment: it must be passed in R1,
        but in non-closures, there is no such argument, so we can't treat all arguments
        the same way: the closure environment is special. Maybe the right step forward
        would be to define a different calling convention for closure arguments.
      o Let-no-escapes need to be emitted out-of-line -- otherwise, we drop code.
      o Respect RTS requirement of word alignment for pointers
        My stack allocation can pack sub-word values into a single word on the stack,
        but it wasn't requiring word-alignment for pointers. It does now,
        by word-aligning both pointer registers and call areas.
      o CmmLint was over-aggresively ruling out non-word-aligned memory references,
        which may be kosher now that we can spill small values into a single word.
      o Wrong label order on a conditional branch when compiling switches.
      o void args weren't dropped in many cases.
        To help prevent this kind of mistake, I defined a NonVoid wrapper,
        which I'm applying only to Id's for now, although there are probably
        other good candidates.
      o A little code refactoring: separate modules for procpoint analysis splitting, 
        stack layout, and building infotables.
      o Stack limit check: insert along with the heap limit check, using a symbolic
        constant (a special CmmLit), then replace it when the stack layout is known.
      o Removed last node: MidAddToContext 
      o Adding block id as a literal: means that the lowering of the calling conventions
        no longer has to produce labels early, which was inhibiting common-block elimination.
        Will also make it easier for the non-procpoint-splitting path.
      o Info tables: don't try to describe the update frame!
      o Over aggressive use of NonVoid!!!!
        Don't drop the non-void args before setting the type of the closure!!!
      o Sanity checking:
        Added a pass to stub dead dead slots on the stack
        (only ~10 lines with the dataflow framework)
      o More sanity checking:
        Check that incoming pointer arguments are non-stubbed.
        Note: these checks are still subject to dead-code removal, but they should
        still be quite helpful.
      o Better sanity checking: why stop at function arguments?
        Instead, in mkAssign, check that _any_ assignment to a pointer type is non-null
        -- the sooner the crash, the easier it is to debug.
        Still need to add the debugging flag to turn these checks on explicitly.
      o Fixed yet another calling convention bug.
        This time, the calls to the GC were wrong. I've added a new convention
        for GC calls and invoked it where appropriate.
        We should really straighten out the calling convention stuff:
          some of the code (and documentation) is spread across the compiler,
          and there's some magical use of the node register that should really
          be handled (not avoided) by calling conventions.
      o Switch bug: the arms in mkCmmLitSwitch weren't returning to a single join point.
      o Environment shadowing problem in Stg->Cmm:
        When a closure f is bound at the top-level, we should not bind f to the
        node register on entry to the closure.
        Why? Because if the body of f contains a let-bound closure g that refers
        to f, we want to make sure that it refers to the static closure for f.
        Normally, this would all be fine, because when we compile a closure,
        we rebind free variables in the environment. But f doesn't look like
        a free variable because it's a static value. So, the binding for f
        remains in the environment when we compile g, inconveniently referring
        to the wrong thing.
        Now, I bind the variable in the local environment only if the closure is not
        bound at the top level. It's still okay to make assumptions about the
        node holding the closure environment; we just won't find the binding
        in the environment, so code that names the closure will now directly
        get the label of the static closure, not the node register holding a
        pointer to the static closure.
      o Don't generate bogus Cmm code containing SRTs during the STG -> Cmm pass!
        The tables made reference to some labels that don't exist when we compute and
        generate the tables in the back end.
      o Safe foreign calls need some special treatment (at least until we have the integrated
        codegen). In particular:
        o they need info tables
        o they are not procpoints -- the successor had better be in the same procedure
        o we cannot (yet) implement the calling conventions early, which means we have
          to carry the calling-conv info all the way to the end
      o We weren't following the old convention when registering a module.
        Now, we use update frames to push any new modules that have to be registered
        and enter the youngest one on the stack.
        We also use the update frame machinery to specify that the return should pop
        the return address off the stack.
      o At each safe foreign call, an infotable must be at the bottom of the stack,
        and the TSO->sp must point to it.
      o More problems with void args in a direct call to a function:
        We were checking the args (minus voids) to check whether the call was saturated,
        which caused problems when the function really wasn't saturated because it
        took an extra void argument.
      o Forgot to distinguish integer != from floating != during Stg->Cmm
      o Updating slotEnv and areaMap to include safe foreign calls
        The dataflow analyses that produce the slotEnv and areaMap give
        results for each basic block, but we also need the results for
        a safe foreign call, which is a middle node.
        After running the dataflow analysis, we have another pass that
        updates the results to includ any safe foreign calls.
      o Added a static flag for the debugging technique that inserts
        instructions to stub dead slots on the stack and crashes when
        a stubbed value is loaded into a pointer-typed LocalReg.
      o C back end expects to see return continuations before their call sites.
        Sorted the flowgraphs appropriately after splitting.
      o PrimOp calling conventions are special -- unlimited registers, no stack
        Yet another calling convention...
      o More void value problems: if the RHS of a case arm is a void-typed variable,
        don't try to return it.
      o When calling some primOp, they may allocate memory; if so, we need to
        do a heap check when we return from the call.
      e6243a81
  21. 14 Aug, 2008 1 commit
    • dias@eecs.harvard.edu's avatar
      Merging in the new codegen branch · 176fa33f
      dias@eecs.harvard.edu authored
      This merge does not turn on the new codegen (which only compiles
      a select few programs at this point),
      but it does introduce some changes to the old code generator.
      
      The high bits:
      1. The Rep Swamp patch is finally here.
         The highlight is that the representation of types at the
         machine level has changed.
         Consequently, this patch contains updates across several back ends.
      2. The new Stg -> Cmm path is here, although it appears to have a
         fair number of bugs lurking.
      3. Many improvements along the CmmCPSZ path, including:
         o stack layout
         o some code for infotables, half of which is right and half wrong
         o proc-point splitting
      176fa33f
  22. 29 May, 2008 2 commits
    • dias@eecs.harvard.edu's avatar
      Replacing copyins and copyouts with data-movement instructions · 0d80489c
      dias@eecs.harvard.edu authored
      o Moved BlockId stuff to a new file to avoid module recursion
      o Defined stack areas for parameter-passing locations and spill slots
      o Part way through replacing copy in and copy out nodes
        - added movement instructions for stack pointer
        - added movement instructions for call and return parameters
          (but not with the proper calling conventions)
      o Inserting spills and reloads for proc points is now procpoint-aware
        (it was relying on the presence of a CopyIn node as a proxy for
         procpoint knowledge)
      o Changed ZipDataflow to expect AGraphs (instead of being polymorphic in
         the type of graph)
      0d80489c
    • dias@eecs.harvard.edu's avatar
      Cmm back end upgrades · 25628e27
      dias@eecs.harvard.edu authored
      Several changes in this patch, partially bug fixes, partially new code:
      o bug fixes in ZipDataflow
         - added some checks to verify that facts converge
         - removed some erroneous checks of convergence on entry nodes
         - added some missing applications of transfer functions
      o changed dataflow clients to use ZipDataflow, making ZipDataflow0 obsolete
      o eliminated DFA monad (no need for separate analysis and rewriting monads with ZipDataflow)
      o started stack layout changes
         - no longer generating CopyIn and CopyOut nodes (not yet fully expunged though)
         - still not using proper calling conventions
      o simple new optimizations:
         - common block elimination
            -- have not yet tried to move the Adams opt out of CmmProcPointZ
         - block concatenation
      o piped optimization fuel up to the HscEnv
         - can be limited by a command-line flag
         - not tested, and probably not yet properly used by clients
      o added unique supply to FuelMonad, also lifted unique supply to DFMonad
      25628e27