[Git][ghc/ghc][wip/romes/step-out-11] 57 commits: Specialise: Improve specialisation by refactoring interestingDict

Rodrigo Mesquita pushed to branch wip/romes/step-out-11 at Glasgow Haskell Compiler / GHC Commits: f707bab4 by Andreas Klebinger at 2025-07-12T14:56:16+01:00 Specialise: Improve specialisation by refactoring interestingDict This MR addresses #26051, which concerns missed type-class specialisation. The main payload of the MR is to completely refactor the key function `interestingDict` in GHC.Core.Opt.Specialise The main change is that we now also look at the structure of the dictionary we consider specializing on, rather than only the type. See the big `Note [Interesting dictionary arguments]` - - - - - ca7a9d42 by Simon Peyton Jones at 2025-07-12T14:56:16+01:00 Treat tuple dictionaries uniformly; don't unbox them See `Note [Do not unbox class dictionaries]` in DmdAnal.hs, sep (DNB1). This MR reverses the plan in #23398, which suggested a special case to unbox tuple dictionaries in worker/wrapper. But: - This was the cause of a pile of complexity in the specialiser (#26158) - Even with that complexity, specialision was still bad, very bad See https://gitlab.haskell.org/ghc/ghc/-/issues/19747#note_626297 And it's entirely unnecessary! Specialision works fine without unboxing tuple dictionaries. - - - - - be7296c9 by Andreas Klebinger at 2025-07-12T14:56:16+01:00 Remove complex special case from the type-class specialiser There was a pretty tricky special case in Specialise which is no longer necessary. * Historical Note [Floating dictionaries out of cases] * #26158 * #19747 https://gitlab.haskell.org/ghc/ghc/-/issues/19747#note_626297 This MR removes it. Hooray. - - - - - 4acf3a86 by Ben Gamari at 2025-07-15T05:46:32-04:00 configure: bump version to 9.15 - - - - - 45efaf71 by Teo Camarasu at 2025-07-15T05:47:13-04:00 rts/nonmovingGC: remove n_free We remove the nonmovingHeap.n_free variable. We wanted this to track the length of nonmovingHeap.free. But this isn't possible to do atomically. When this isn't accurate we can get a segfault by going past the end of the list. Instead, we just count the length of the list when we grab it in nonmovingPruneFreeSegment. Resolves #26186 - - - - - c635f164 by Ben Gamari at 2025-07-15T14:05:54-04:00 configure: Drop probing of ld.gold As noted in #25716, `gold` has been dropped from binutils-2.44. Fixes #25716. Metric Increase: size_hello_artifact_gzip size_hello_unicode_gzip ghc_prim_so - - - - - 637bb538 by Ben Gamari at 2025-07-15T14:05:55-04:00 testsuite/recomp015: Ignore stderr This is necessary since ld.bfd complains that we don't have a .note.GNU-stack section, potentially resulting in an executable stack. - - - - - d3cd4ec8 by Wen Kokke at 2025-07-15T14:06:39-04:00 Fix documentation for heap profile ID - - - - - 73082769 by Ben Gamari at 2025-07-15T16:56:38-04:00 Bump win32-tarballs to v0.9 - - - - - 3b63b254 by Ben Gamari at 2025-07-15T16:56:39-04:00 rts/LoadArchive: Handle null terminated string tables As of `llvm-ar` now emits filename tables terminated with null characters instead of the usual POSIX `/\n` sequence. Fixes #26150. - - - - - 195f6527 by Tamar Christina at 2025-07-15T16:56:39-04:00 rts: rename label so name doesn't conflict with param - - - - - 63373b95 by Tamar Christina at 2025-07-15T16:56:39-04:00 rts: Handle API set symbol versioning conflicts - - - - - 48e9aa3e by Tamar Christina at 2025-07-15T16:56:39-04:00 rts: Mark API set symbols as HIDDEN and correct symbol type - - - - - 959e827a by Tamar Christina at 2025-07-15T16:56:39-04:00 rts: Implement WEAK EXTERNAL undef redirection by target symbol name - - - - - 65f19293 by Ben Gamari at 2025-07-15T16:56:39-04:00 rts/LoadArchive: Handle string table entries terminated with / llvm-ar appears to terminate string table entries with `/\n` [1]. This matters in the case of thin archives, since the filename is used. In the past this worked since `llvm-ar` would produce archives with "small" filenames when possible. However, now it appears to always use the string table. [1] https://github.com/llvm/llvm-project/blob/bfb686bb5ba503e9386dc899e1ebbe2488... - - - - - 9cbb3ef5 by Ben Gamari at 2025-07-15T16:56:39-04:00 testsuite: Mark T12497 as fixed Thanks to the LLVM toolchain update. Closes #22694. - - - - - 2854407e by Ben Gamari at 2025-07-15T16:56:39-04:00 testsuite: Accept new output of T11223_link_order_a_b_2_fail on Windows The archive member number changed due to the fact that llvm-ar now uses a string table. - - - - - 28439593 by Ben Gamari at 2025-07-15T16:56:39-04:00 rts/linker/PEi386: Implement IMAGE_REL_AMD64_SECREL This appears to now be used by libc++ as distributed by msys2. - - - - - 2b053755 by Tamar Christina at 2025-07-15T16:56:39-04:00 rts: Cleanup merge resolution residue in lookupSymbolInDLL_PEi386 and make safe without dependent - - - - - e8acd2e7 by Wen Kokke at 2025-07-16T08:37:04-04:00 Remove the `profile_id` parameter from various RTS functions. Various RTS functions took a `profile_id` parameter, intended to be used to distinguish parallel heap profile breakdowns (e.g., `-hT` and `-hi`). However, this feature was never implemented and the `profile_id` parameter was set to 0 throughout the RTS. This commit removes the parameter but leaves the hardcoded profile ID in the functions that emit the encoded eventlog events as to not change the protocol. The affected functions are `traceHeapProfBegin`, `postHeapProfBegin`, `traceHeapProfSampleString`, `postHeapProfSampleString`, `traceHeapProfSampleCostCentre`, and `postHeapProfSampleCostCentre`. - - - - - 76d392a2 by Wen Kokke at 2025-07-16T08:37:04-04:00 Make `traceHeapProfBegin` an init event. - - - - - bbaa44a7 by Peng Fan at 2025-07-16T16:50:42-04:00 NCG/LA64: Support finer-grained DBAR hints For LA664 and newer uarchs, they have made finer granularity hints available: Bit4: ordering or completion (0: completion, 1: ordering) Bit3: barrier for previous read (0: true, 1: false) Bit2: barrier for previous write (0: true, 1: false) Bit1: barrier for succeeding read (0: true, 1: false) Bit0: barrier for succeeding write (0: true, 1: false) And not affect the existing models because other hints are treated as 'dbar 0' there. - - - - - 7da86e16 by Andreas Klebinger at 2025-07-16T16:51:25-04:00 Disable -fprof-late-overloaded-calls for join points. Currently GHC considers cost centres as destructive to join contexts. Or in other words this is not considered valid: join f x = ... in ... -> scc<tick> jmp This makes the functionality of `-fprof-late-overloaded-calls` not feasible for join points in general. We used to try to work around this by putting the ticks on the rhs of the join point rather than around the jump. However beyond the loss of accuracy this was broken for recursive join points as we ended up with something like: rec-join f x = scc<tick> ... jmp f x Which similarly is not valid as the tick once again destroys the tail call. One might think we could limit ourselves to non-recursive tail calls and do something clever like: join f x = scc<tick> ... in ... jmp f x And sometimes this works! But sometimes the full rhs would look something like: join g x = .... join f x = scc<tick> ... -> jmp g x Which, would again no longer be valid. I believe in the long run we can make cost centre ticks non-destructive to join points. Or we could keep track of where we are/are not allowed to insert a cost centre. But in the short term I will simply disable the annotation of join calls under this flag. - - - - - 7ee22fd5 by ARATA Mizuki at 2025-07-17T06:05:30-04:00 x86 NCG: Better lowering for shuffleFloatX4# and shuffleDoubleX2# The new implementation * make use of specialized instructions like (V)UNPCK{L,H}{PS,PD}, and * do not require -mavx. Close #26096 Co-authored-by: sheaf - - - - - c6cd2da1 by Jappie Klooster at 2025-07-17T06:06:20-04:00 Update interact docs to explain about buffering We need to tell the user to set to the appropriate buffer format. Otherwise, this function may get randomly stuck, or just behave confusingly. issue: https://gitlab.haskell.org/ghc/ghc/-/issues/26131 NB, I'm running this with cabal *NOT* ghci. ghci messes with buffering anyway. ```haskell interaction :: String -> String interaction "jappie" = "hi" interaction "jakob" = "hello" interaction x = "unkown input: " <> x main :: IO () main = interact interaction ``` so in my input (prefixed by `>`) I get: ```

jappie unkown input: jappie

we confirmed later this was due to lack of \n matching.
Anyway movnig on to more unexpected stuff:

```haskell
main :: IO ()
main = do
  interact  (concatMap interaction . lines)

get's stuck forever. actually `^D` (ctrl+d) unstucks it and runs all input as expected. for example you can get: ```

sdfkds fakdsf unkown input: sdfkdsunkown input: fakdsf

This program works!
```haskell
interaction :: String -> String
interaction "jappie" = "hi \n"
interaction "jakob" = "hello \n"
interaction x = "unkown input: " <> x <> "\n"

main :: IO ()
main = do
  interact  (concatMap interaction . lines)

the reason is that linebuffering is set for both in and output by default. so lines eats the input lines, and all the \n postfixes make sure the buffer is put out. - - - - - 9fa590a6 by Zubin Duggal at 2025-07-17T06:07:03-04:00 fetch_gitlab: Ensure we copy users_guide.pdf and Haddock.pdf to the release docs directory Fixes #24093 - - - - - cc650b4b by Andrew Lelechenko at 2025-07-17T12:30:24-04:00 Add Data.List.NonEmpty.mapMaybe As per https://github.com/haskell/core-libraries-committee/issues/337 - - - - - 360fa82c by Duncan Coutts at 2025-07-17T12:31:14-04:00 base: Deprecate GHC.Weak.Finalize.runFinalizerBatch https://github.com/haskell/core-libraries-committee/issues/342 - - - - - f4e8466c by Alan Zimmerman at 2025-07-17T12:31:55-04:00 EPA: Update exact printing based on GHC 9.14 tests As a result of migrating the GHC ghc-9.14 branch tests to ghc-exactprint in https://github.com/alanz/ghc-exactprint/tree/ghc-9.14, a couple of discrepancies were picked up - The opening paren for a DefaultDecl was printed in the wrong place - The import declaration level specifiers were not printed. This commit adds those fixes, and some tests for them. The tests brought to light that the ImportDecl ppr instance had not been updated for level specifiers, so it updates that too. - - - - - 8b731e3c by Matthew Pickering at 2025-07-21T13:36:43-04:00 level imports: Fix infinite loop with cyclic module imports I didn't anticipate that downsweep would run before we checked for cyclic imports. Therefore we need to use the reachability function which handles cyclic graphs. Fixes #26087 - - - - - d751a9f1 by Pierre Thierry at 2025-07-21T13:37:28-04:00 Fix documentation about deriving from generics - - - - - f8d9d016 by Andrew Lelechenko at 2025-07-22T21:13:28-04:00 Fix issues with toRational for types capable to represent infinite and not-a-number values This commit fixes all of the following pitfalls:

toRational (read "Infinity" :: Double) 179769313486231590772930519078902473361797697894230657273430081157732675805500963132708477322407536021120113879871393357658789768814416622492847430639474124377767893424865485276302219601246094119453082952085005768838150682342462881473913110540827237163350510684586298239947245938479716304835356329624224137216 % 1 toRational (read "NaN" :: Double) 269653970229347386159395778618353710042696546841345985910145121736599013708251444699062715983611304031680170819807090036488184653221624933739271145959211186566651840137298227914453329401869141179179624428127508653257226023513694322210869665811240855745025766026879447359920868907719574457253034494436336205824 % 1

realToFrac (read "NaN" :: Double) -- With -O0 Infinity realToFrac (read "NaN" :: Double) -- With -O1 NaN

realToFrac (read "NaN" :: Double) :: CDouble Infinity realToFrac (read "NaN" :: CDouble) :: Double Infinity

Implements https://github.com/haskell/core-libraries-committee/issues/338 - - - - - 5dabc718 by Zubin Duggal at 2025-07-22T21:14:10-04:00 haddock: Don't warn about missing link destinations for derived names. Fixes #26114 - - - - - 9c3a0937 by Matthew Pickering at 2025-07-22T21:14:52-04:00 template haskell: use a precise condition when implicitly lifting Implicit lifting corrects a level error by replacing references to `x` with `$(lift x)`, therefore you can use a level `n` binding at level `n + 1`, if it can be lifted. Therefore, we now have a precise check that the use level is 1 more than the bind level. Before this bug was not observable as you only had 0 and 1 contexts but it is easily evident when using explicit level imports. Fixes #26088 - - - - - 5144b22f by Andreas Klebinger at 2025-07-22T21:15:34-04:00 Add since tag and more docs for do-clever-arg-eta-expansion Fixes #26113 - - - - - c865623b by Andreas Klebinger at 2025-07-22T21:15:34-04:00 Add since tag for -fexpose-overloaded-unfoldings Fixes #26112 - - - - - 49a44ab7 by Simon Hengel at 2025-07-23T17:59:55+07:00 Refactor GHC.Driver.Errors.printMessages - - - - - 84711c39 by Simon Hengel at 2025-07-23T18:27:34+07:00 Respect `-fdiagnostics-as-json` for error messages from pre-processors (fixes #25480) - - - - - d046b5ab by Simon Hengel at 2025-07-24T06:12:05-04:00 Include the rendered message in -fdiagnostics-as-json output This implements #26173. - - - - - d2b89603 by Ben Gamari at 2025-07-24T06:12:47-04:00 rts/Interpreter: Factor out ctoi tuple info tables into data Instead of a massive case let's put this into data which we can reuse elsewhere. - - - - - 4bc78496 by Sebastian Graf at 2025-07-24T16:19:34-04:00 CprAnal: Detect recursive newtypes (#25944) While `cprTransformDataConWork` handles recursive data con workers, it did not detect the case when a newtype is responsible for the recursion. This is now detected in the `Cast` case of `cprAnal`. The same reproducer made it clear that `isRecDataCon` lacked congruent handling for `AppTy` and `CastTy`, now fixed. Furthermore, the new repro case T25944 triggered this bug via an infinite loop in `cprFix`, caused by the infelicity in `isRecDataCon`. While it should be much less likely to trigger such an infinite loop now that `isRecDataCon` has been fixed, I made sure to abort the loop after 10 iterations and emitting a warning instead. Fixes #25944. - - - - - 0a583689 by Sylvain Henry at 2025-07-24T16:20:26-04:00 STM: don't create a transaction in the rhs of catchRetry# (#26028) We don't need to create a transaction for the rhs of (catchRetry#) because contrary to the lhs we don't need to abort it on retry. Moreover it is particularly harmful if we have code such as (#26028): let cN = readTVar vN >> retry tree = c1 `orElse` (c2 `orElse` (c3 `orElse` ...)) atomically tree Because it will stack transactions for the rhss and the read-sets of all the transactions will be iteratively merged in O(n^2) after the execution of the most nested retry. - - - - - a49eca26 by Simon Peyton Jones at 2025-07-25T09:49:58+01:00 Renaming around predicate types .. we were (as it turned out) abstracting over type-class selectors in SPECIALISATION rules! Wibble isEqPred - - - - - f80375dd by Simon Peyton Jones at 2025-07-25T09:49:58+01:00 Refactor of Specialise.hs This patch just tidies up `specHeader` a bit, removing one of its many results, and adding some comments. No change in behaviour. Also add a few more `HasDebugCallStack` contexts. - - - - - 1bd12371 by Simon Peyton Jones at 2025-07-25T09:49:58+01:00 Improve treatment of SPECIALISE pragmas -- again! This MR does another major refactor of the way that SPECIALISE pragmas work, to fix #26115, #26116, #26117. * We now /always/ solve forall-constraints in an all-or-nothing way. See Note [Solving a Wanted forall-constraint] in GHC.Tc.Solver.Solve This means we might have unsolved quantified constraints, which need to be reported. See `inert_insts` in `getUnsolvedInerts`. * I refactored the short-cut solver for type classes to work by recursively calling the solver rather than by having a little baby solver that kept being not clever enough. See Note [Shortcut solving] in GHC.Tc.Solver.Dict * I totally rewrote the desugaring of SPECIALISE pragmas, again. The new story is in Note [Desugaring new-form SPECIALISE pragmas] in GHC.HsToCore.Binds Both old-form and new-form SPECIALISE pragmas now route through the same function `dsSpec_help`. The tricky function `decomposeRuleLhs` is now used only for user-written RULES, not for SPECIALISE pragmas. * I improved `solveOneFromTheOther` to account for rewriter sets. Previously it would solve a non-rewritten dict from a rewritten one. For equalities we were already dealing with this, in Some incidental refactoring * A small refactor: `ebv_tcvs` in `EvBindsBar` now has a list of coercions, rather than a set of tyvars. We just delay taking the free vars. * GHC.Core.FVs.exprFVs now returns /all/ free vars. Use `exprLocalFVs` for Local vars. Reason: I wanted another variant for /evidence/ variables. * Ues `EvId` in preference to `EvVar`. (Evidence variables are always Ids.) Rename `isEvVar` to `isEvId`. * I moved `inert_safehask` out of `InertCans` and into `InertSet` where it more properly belongs. Compiler-perf changes: * There was a palpable bug (#26117) which this MR fixes in newWantedEvVar, which bypassed all the subtle overlapping-Given and shortcutting logic. (See the new `newWantedEvVar`.) Fixing this but leads to extra dictionary bindings; they are optimised away quickly but they made CoOpt_Read allocate 3.6% more. * Hpapily T15164 improves. * The net compiler-allocation change is 0.0% Metric Decrease: T15164 Metric Increase: CoOpt_Read T12425 - - - - - 953fd8f1 by Simon Peyton Jones at 2025-07-25T09:49:58+01:00 Solve forall-constraints immediately, or not at all This MR refactors the constraint solver to solve forall-constraints immediately, rather than emitting an implication constraint to be solved later. The most immediate motivation was that when solving quantified constraints in SPECIALISE pragmas, we really really don't want to leave behind half- solved implications. Also it's in tune with the approach of the new short-cut solver, which recursively invokes the solver. It /also/ saves quite a bit of plumbing; e.g - The `wl_implics` field of `WorkList` is gone, - The types of `solveSimpleWanteds` and friends are simplified. - An EvFun contains binding, rather than an EvBindsVar ref-cell that will in the future contain bindings. That makes `evVarsOfTerm` simpler. Much nicer. It also improves error messages a bit. All described in Note [Solving a Wanted forall-constraint] in GHC.Tc.Solver.Solve. One tiresome point: in the tricky case of `inferConstraintsCoerceBased` we make a forall-constraint. This we /do/ want to partially solve, so we can infer a suitable context. (I'd be quite happy to force the user to write a context, bt I don't want to change behavior.) So we want to generate an /implication/ constraint in `emitPredSpecConstraints` rather than a /forall-constraint/ as we were doing before. Discussed in (WFA3) of the above Note. Incidental refactoring * `GHC.Tc.Deriv.Infer.inferConstraints` was consulting the state monad for the DerivEnv that the caller had just consulted. Nicer to pass it as an argument I think, so I have done that. No change in behaviour. - - - - - 6921ab42 by Simon Peyton Jones at 2025-07-25T09:49:58+01:00 Remove duplicated code in Ast.hs for evTermFreeVars This is just a tidy up. - - - - - 1165f587 by Simon Peyton Jones at 2025-07-25T09:49:58+01:00 Small tc-tracing changes only - - - - - 0776ffe0 by Simon Hengel at 2025-07-26T04:54:20-04:00 Respect `-fdiagnostics-as-json` for core diagnostics (see #24113) - - - - - cc1116e0 by Andrew Lelechenko at 2025-07-26T04:55:01-04:00 docs: add since pragma to Data.List.NonEmpty.mapMaybe - - - - - 9620cae0 by Rodrigo Mesquita at 2025-07-30T11:11:39+01:00 debugger: Uniquely identify breakpoints by internal id Since b85b11994e0130ff2401dd4bbdf52330e0bcf776 (support inlining breakpoints), a breakpoint has been identified at runtime by *two* pairs of . - The first, aka a 'BreakpointId', uniquely identifies a breakpoint in the source of a module by using the Tick index. A Tick index can index into ModBreaks.modBreaks_xxx to fetch source-level information about where that tick originated. - When a user specifies e.g. a line breakpoint using :break, we'll reverse engineer what a Tick index for that line - We update the `BreakArray` of that module (got from the LoaderState) at that tick index to `breakOn`. - A BCO we can stop at is headed by a BRK_FUN instruction. This instruction stores in an operand the `tick index` it is associated to. We look it up in the associated `BreakArray` (also an operand) and check wheter it was set to `breakOn`. - The second, aka the `ibi_info_mod` + `ibi_info_ix` of the `InternalBreakpointId`, uniquely index into the `imodBreaks_breakInfo` -- the information we gathered during code generation about the existing breakpoint *ocurrences*. - Note that with optimisation there may be many occurrences of the same source-tick-breakpoint across different modules. The `ibi_info_ix` is unique per occurrence, but the `bi_tick_ix` may be shared. See Note [Breakpoint identifiers] about this. - Note that besides the tick ids, info ids are also stored in `BRK_FUN` so the break handler can refer to the associated `CgBreakInfo`. In light of that, the driving changes come from the desire to have the info_id uniquely identify the breakpoint at runtime, and the source tick id being derived from it: - An InternalBreakpointId should uniquely identify a breakpoint just from the code-generation identifiers of `ibi_info_ix` and `ibi_info_mod`. So we drop `ibi_tick_mod` and `ibi_tick_ix`. - A BRK_FUN instruction need only record the "internal breakpoint id", not the tick-level id. So we drop the tick mod and tick index operands. - A BreakArray should be indexed by InternalBreakpointId rather than BreakpointId That means we need to do some more work when setting a breakpoint. Specifically, we need to figure out the internal ids (occurrences of a breakpoint) from the source-level BreakpointId we want to set the breakpoint at (recall :break refers to breaks at the source level). Besides this change being an improvement to the handling of breakpoints (it's clearer to have a single unique identifier than two competing ones), it unlocks the possibility of generating "internal" breakpoints during Cg (needed for #26042). It should also be easier to introduce multi-threaded-aware `BreakArrays` following this change (needed for #26064). Se also the new Note [ModBreaks vs InternalModBreaks] - - - - - 586e7ea0 by Rodrigo Mesquita at 2025-07-30T11:11:39+01:00 cleanup: Move dehydrateCgBreakInfo to Stg2Bc This no longer has anything to do with Core. - - - - - 09f39496 by Rodrigo Mesquita at 2025-07-30T11:11:39+01:00 rts/Disassembler: Fix spacing of BRK_FUN - - - - - 519b71e2 by Rodrigo Mesquita at 2025-07-30T11:11:40+01:00 debugger: Fix bciPtr in Step-out We need to use `BCO_NEXT` to move bciPtr to ix=1, because ix=0 points to the instruction itself! I do not understand how this didn't crash before. - - - - - b8ed860a by Rodrigo Mesquita at 2025-07-30T11:11:40+01:00 debugger: Allow BRK_FUNs to head case continuation BCOs When we start executing a BCO, we may want to yield to the scheduler: this may be triggered by a heap/stack check, context switch, or a breakpoint. To yield, we need to put the stack in a state such that when execution is resumed we are back to where we yielded from. Previously, a BKR_FUN could only head a function BCO because we only knew how to construct a valid stack for yielding from one -- simply add `apply_interp_info` + the BCO to resume executing. This is valid because the stack at the start of run_BCO is headed by that BCO's arguments. However, in case continuation BCOs (as per Note [Case continuation BCOs]), we couldn't easily reconstruct a valid stack that could be resumed because we dropped too soon the stack frames regarding the value returned (stg_ret) and received (stg_ctoi) by that continuation. This is especially tricky because of the variable type and size return frames (e.g. pointer ret_p/ctoi_R1p vs a tuple ret_t/ctoi_t2). The trick to being able to yield from a BRK_FUN at the start of a case cont BCO is to stop removing the ret frame headers eagerly and instead keep them until the BCO starts executing. The new layout at the start of a case cont. BCO is described by the new Note [Stack layout when entering run_BCO]. Now, we keep the ret_* and ctoi_* frames when entering run_BCO. A BRK_FUN is then executed if found, and the stack is yielded as-is with the preserved ret and ctoi frames. Then, a case cont BCO's instructions always SLIDE off the headers of the ret and ctoi frames, in StgToByteCode.doCase, turning a stack like | .... | +---------------+ | fv2 | +---------------+ | fv1 | +---------------+ | BCO | +---------------+ | stg_ctoi_ret_ | +---------------+ | retval | +---------------+ | stg_ret_..... | +---------------+ into | .... | +---------------+ | fv2 | +---------------+ | fv1 | +---------------+ | retval | +---------------+ for the remainder of the BCO. Moreover, this more uniform approach of keeping the ret and ctoi frames means we need less ad-hoc logic concerning the variable size of ret_tuple vs ret_p/np frames in the code generator and interpreter: Always keep the return to cont. stack intact at the start of run_BCO, and the statically generated instructions will take care of adjusting it. Unlocks BRK_FUNs at the start of case cont. BCOs which will enable a better user-facing step-out (#26042) which is free of the bugs the current BRK_ALTS implementation suffers from (namely, using BRK_FUN rather than BRK_ALTS in a case cont. means we'll never accidentally end up in a breakpoint "deeper" than the continuation, because we stop at the case cont itself rather than on the first breakpoint we evaluate after it). - - - - - bed90fb6 by Rodrigo Mesquita at 2025-07-30T11:11:40+01:00 BRK_FUN with InternalBreakLocs for code-generation time breakpoints At the start of a case continuation BCO, place a BRK_FUN. This BRK_FUN uses the new "internal breakpoint location" -- allowing us to come up with a valid source location for this breakpoint that is not associated with a source-level tick. For case continuation BCOs, we use the last tick seen before it as the source location. The reasoning is described in Note [Debugger: Stepout internal break locs]. Note how T26042c, which was broken because it displayed the incorrect behavior of the previous step out when we'd end up at a deeper level than the one from which we initiated step-out, is now fixed. As of this commit, BRK_ALTS is now dead code and is thus dropped. Note [Debugger: Stepout internal break locs] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Step-out tells the interpreter to run until the current function returns to where it was called from, and stop there. This is achieved by enabling the BRK_FUN found on the first RET_BCO frame on the stack (See [Note Debugger: Step-out]). Case continuation BCOs (which select an alternative branch) must therefore be headed by a BRK_FUN. An example: f x = case g x of <--- end up here 1 -> ... 2 -> ... g y = ... <--- step out from here - `g` will return a value to the case continuation BCO in `f` - The case continuation BCO will receive the value returned from g - Match on it and push the alternative continuation for that branch - And then enter that alternative. If we step-out of `g`, the first RET_BCO on the stack is the case continuation of `f` -- execution should stop at its start, before selecting an alternative. (One might ask, "why not enable the breakpoint in the alternative instead?", because the alternative continuation is only pushed to the stack *after* it is selected by the case cont. BCO) However, the case cont. BCO is not associated with any source-level tick, it is merely the glue code which selects alternatives which do have source level ticks. Therefore, we have to come up at code generation time with a breakpoint location ('InternalBreakLoc') to display to the user when it is stopped there. Our solution is to use the last tick seen just before reaching the case continuation. This is robust because a case continuation will thus always have a relevant breakpoint location: - The source location will be the last source-relevant expression executed before the continuation is pushed - So the source location will point to the thing you've just stepped out of - Doing :step-local from there will put you on the selected alternative (which at the source level may also be the e.g. next line in a do-block) Examples, using angle brackets (<<...>>) to denote the breakpoint span: f x = case <<g x>> {- step in here -} of 1 -> ... 2 -> ...> g y = <<...>> <--- step out from here ... f x = < ... 2 -> ...>> doing :step-local ... f x = case g x of 1 -> <<...>> <--- stop in the alternative 2 -> ... A second example based on T26042d2, where the source is a do-block IO action, optimised to a chain of `case expressions`. main = do putStrLn "hello1" <<f>> <--- step-in here putStrLn "hello3" putStrLn "hello4" f = do <> <--- step-out from here putStrLn "hello2.2" ... main = do putStrLn "hello1" <<f>> <--- end up here again, the previously executed expression putStrLn "hello3" putStrLn "hello4" doing step/step-local ... main = do putStrLn "hello1" f <> <--- straight to the next line putStrLn "hello4" Finishes #26042 - - - - - 78f06878 by Rodrigo Mesquita at 2025-07-30T11:11:40+01:00 bytecode: Don't PUSH_L 0; SLIDE 1 1 While looking through bytecode I noticed a quite common unfortunate pattern: ... PUSH_L 0 SLIDE 1 1 We do this often by generically constructing a tail call from a function atom that may be somewhere arbitrary on the stack. However, for the special case that the function can be found directly on top of the stack, as part of the arguments, it's plain redundant to push then slide it. In this commit we add a small optimisation to the generation of tailcalls in bytecode. Simply: lookahead for the function in the stack. If it is the first thing on the stack and it is part of the arguments which would be dropped as we entered the tail call, then don't push then slide it. In a simple example (T26042b), this already produced a drastic improvement in generated code (left is old, right is with this patch): ```diff 3c3 < 2025-07-29 10:14:02.081277 UTC ---

2025-07-29 10:50:36.560949 UTC 160,161c160 < PUSH_L 0 < SLIDE 1 2

SLIDE 1 1

164,165d162 < PUSH_L 0 < SLIDE 1 1 175,176c172 < PUSH_L 0 < SLIDE 1 2 ---

SLIDE 1 1

179,180d174 < PUSH_L 0 < SLIDE 1 1 206,207d199 < PUSH_L 0 < SLIDE 1 1 210,211d201 < PUSH_L 0 < SLIDE 1 1 214,215d203 < PUSH_L 0 < SLIDE 1 1 218,219d205 < PUSH_L 0 < SLIDE 1 1 222,223d207 < PUSH_L 0 < SLIDE 1 1 ... 600,601c566 < PUSH_L 0 < SLIDE 1 2 ---

SLIDE 1 1

604,605d568 < PUSH_L 0 < SLIDE 1 1 632,633d594 < PUSH_L 0 < SLIDE 1 1 636,637d596 < PUSH_L 0 < SLIDE 1 1 640,641d598 < PUSH_L 0 < SLIDE 1 1 644,645d600 < PUSH_L 0 < SLIDE 1 1 648,649d602 < PUSH_L 0 < SLIDE 1 1 652,653d604 < PUSH_L 0 < SLIDE 1 1 656,657d606 < PUSH_L 0 < SLIDE 1 1 660,661d608 < PUSH_L 0 < SLIDE 1 1 664,665d610 < PUSH_L 0 < SLIDE 1 1 ``` I also compiled lib:Cabal to bytecode and counted the number of bytecode lines with `find dist-newstyle -name "*.dump-BCOs" -exec wc {} +`: with unoptimized core: 1190689 lines (before) - 1172891 lines (now) = 17798 less redundant instructions (-1.5%) with optimized core: 1924818 lines (before) - 1864836 lines (now) = 59982 less redundant instructions (-3.1%) - - - - - 217 changed files: - .gitlab/rel_eng/fetch-gitlab-artifacts/fetch_gitlab.py - compiler/GHC/ByteCode/Asm.hs - compiler/GHC/ByteCode/Breakpoints.hs - compiler/GHC/ByteCode/Instr.hs - compiler/GHC/ByteCode/Linker.hs - compiler/GHC/ByteCode/Types.hs - compiler/GHC/CmmToAsm/LA64/CodeGen.hs - compiler/GHC/CmmToAsm/LA64/Instr.hs - compiler/GHC/CmmToAsm/LA64/Ppr.hs - compiler/GHC/CmmToAsm/X86/CodeGen.hs - compiler/GHC/CmmToAsm/X86/Instr.hs - compiler/GHC/CmmToAsm/X86/Ppr.hs - compiler/GHC/Core.hs - compiler/GHC/Core/FVs.hs - compiler/GHC/Core/LateCC/OverloadedCalls.hs - compiler/GHC/Core/Make.hs - compiler/GHC/Core/Opt/Arity.hs - compiler/GHC/Core/Opt/CprAnal.hs - compiler/GHC/Core/Opt/DmdAnal.hs - compiler/GHC/Core/Opt/Monad.hs - compiler/GHC/Core/Opt/SpecConstr.hs - compiler/GHC/Core/Opt/Specialise.hs - compiler/GHC/Core/Opt/WorkWrap/Utils.hs - compiler/GHC/Core/Predicate.hs - compiler/GHC/Core/Rules.hs - compiler/GHC/Core/Subst.hs - compiler/GHC/Core/TyCo/Rep.hs - compiler/GHC/Core/Unfold/Make.hs - compiler/GHC/Core/Utils.hs - compiler/GHC/CoreToIface.hs - compiler/GHC/Driver/Errors.hs - compiler/GHC/Hs/ImpExp.hs - compiler/GHC/HsToCore/Binds.hs - compiler/GHC/HsToCore/Breakpoints.hs - compiler/GHC/HsToCore/Errors/Ppr.hs - compiler/GHC/HsToCore/Pmc/Solver/Types.hs - compiler/GHC/Iface/Ext/Ast.hs - compiler/GHC/Linker/Loader.hs - compiler/GHC/Parser.y - compiler/GHC/Rename/Splice.hs - compiler/GHC/Runtime/Debugger/Breakpoints.hs - compiler/GHC/Runtime/Eval.hs - compiler/GHC/Runtime/Interpreter.hs - compiler/GHC/StgToByteCode.hs - compiler/GHC/SysTools/Process.hs - compiler/GHC/Tc/Deriv.hs - compiler/GHC/Tc/Deriv/Infer.hs - compiler/GHC/Tc/Deriv/Utils.hs - compiler/GHC/Tc/Errors.hs - compiler/GHC/Tc/Errors/Ppr.hs - compiler/GHC/Tc/Gen/App.hs - compiler/GHC/Tc/Gen/Expr.hs - compiler/GHC/Tc/Gen/Pat.hs - compiler/GHC/Tc/Gen/Sig.hs - compiler/GHC/Tc/Solver.hs - compiler/GHC/Tc/Solver/Default.hs - compiler/GHC/Tc/Solver/Dict.hs - compiler/GHC/Tc/Solver/Equality.hs - compiler/GHC/Tc/Solver/InertSet.hs - compiler/GHC/Tc/Solver/Monad.hs - compiler/GHC/Tc/Solver/Rewrite.hs - compiler/GHC/Tc/Solver/Solve.hs - + compiler/GHC/Tc/Solver/Solve.hs-boot - compiler/GHC/Tc/Solver/Types.hs - compiler/GHC/Tc/TyCl/PatSyn.hs - compiler/GHC/Tc/Types/Constraint.hs - compiler/GHC/Tc/Types/Evidence.hs - compiler/GHC/Tc/Types/Origin.hs - 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testsuite/tests/roles/should_fail/RolesIArray.stderr - testsuite/tests/rts/all.T - testsuite/tests/rts/linker/T11223/T11223_link_order_a_b_2_fail.stderr-ws-32-mingw32 - testsuite/tests/rts/linker/T11223/T11223_link_order_a_b_2_fail.stderr-ws-64-mingw32 - testsuite/tests/simd/should_run/all.T - + testsuite/tests/simd/should_run/doublex2_shuffle.hs - + testsuite/tests/simd/should_run/doublex2_shuffle.stdout - + testsuite/tests/simd/should_run/doublex2_shuffle_baseline.hs - + testsuite/tests/simd/should_run/doublex2_shuffle_baseline.stdout - + testsuite/tests/simd/should_run/floatx4_shuffle.hs - + testsuite/tests/simd/should_run/floatx4_shuffle.stdout - + testsuite/tests/simd/should_run/floatx4_shuffle_baseline.hs - + testsuite/tests/simd/should_run/floatx4_shuffle_baseline.stdout - + testsuite/tests/simplCore/should_compile/T26051.hs - + testsuite/tests/simplCore/should_compile/T26051.stderr - + testsuite/tests/simplCore/should_compile/T26051_Import.hs - + testsuite/tests/simplCore/should_compile/T26115.hs - 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testsuite/tests/typecheck/should_fail/T18640b.stderr - testsuite/tests/typecheck/should_fail/T19627.stderr - testsuite/tests/typecheck/should_fail/T21530b.stderr - testsuite/tests/typecheck/should_fail/T22912.stderr - testsuite/tests/typecheck/should_fail/tcfail174.stderr - utils/check-exact/ExactPrint.hs - utils/ghc-toolchain/src/GHC/Toolchain/Tools/Link.hs - utils/haddock/haddock-api/haddock-api.cabal - utils/haddock/haddock-api/src/Haddock/Interface/Rename.hs The diff was not included because it is too large. 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