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57186d18
by Rodrigo Mesquita at 2026-08-15T02:49:34-04:00
loopImports: Don't dup ms_uid in summary imports
We were writing the ms_unitid of the mod summary with every single
import of that module
That complicated the code (as though the UnitId in that list could ever
be something else) and also allocates unnecessarily per every mod
import. Very slight allocation decrease measured locally in a few tests:
(MultiComponentModulesRecomp: -0.06%; MultiComponentModulesRecomp100: -0.05%)
Purely a clean up.
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389eeb13
by Rodrigo Mesquita at 2026-08-15T02:49:34-04:00
downsweep: make control flow simpler and cache correct
This refactor extracts the control flow of downsweep into a single
function `dfsBuild`, which takes care of iteratively expanding and
traversing all nodes of the in-construction module graph necessary to
build a full `ModuleGraph`.
There are three levels of caching going on, all of which are necessary
to make sure we don't do repeated work (notably, NEVER summarise the
same module twice).
1. `dfsBuild` accumulates the final module graph and never revisits the
same node of the module graph. Cache is keyed by the final
`ModuleGraph`s `NodeKey`s.
2. For Module A in home-unit u1, each import in the list of imports
needs to be *found* (call to `findImportedModuleWithIsBoot`): at this
point, we only have the `ModuleName` of the import, not the `Module`.
This *finding* is somewhat expensive, so we cache it as well
(`ImportsCache`). The cache key is the home-unit to which the module
belongs~[1], the import package qualifier, and the ModuleName.
[1] Different home-units will have different package flags, which means
potentially different `Module` resolution for the same `ModuleName`.
3. The most expensive operation we want to avoid is summarising a
`Module` into a `ModSummary`, which notably involves parsing the
module header from scratch.
The third cache, in essence, maps a `Module` to its `ModSummary`
(named `ModSummaryCache`). This cache upholds the invariant: we NEVER
summarise the same module twice. In practice, the cache key is the
Module's UnitId and the Source path; the reason is we need to
distinguish between `.hs` and `.hs-boot` files, as their summaries
will differ.
Note that (2) can't guarantee this alone: Two ModuleName imports in
separate units can (and likely do) map to the same `Module`.
Note that the previous implementation failed to achieve the
no-duplicate-work summarisation invariant, and we ended up doing a
quadratic amount of processing in scenarios like test
`MultiComponentModules100`.
See also Note [Downsweep Control Flow and Caching]
Fixes #27461
Perf changes:
MultiComponentModules(normal) ghc/alloc 2,097,389,264 1,992,186,736 -5.0% GOOD
MultiComponentModules100(normal) ghc/alloc 24,310,173,770 21,293,867,360 -12.4% GOOD
MultiComponentModulesRecomp(normal) ghc/alloc 602,761,394 498,543,984 -17.3% GOOD
MultiComponentModulesRecomp100(normal) ghc/alloc 11,885,968,240 8,895,404,864 -25.2% GOOD
-------------------------
Metric Decrease:
MultiComponentModules
MultiComponentModules100
MultiComponentModulesRecomp
MultiComponentModulesRecomp100
-------------------------
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dcf199ce
by Rodrigo Mesquita at 2026-08-15T02:49:34-04:00
implicitRequirementsShallow can never reach HoleUnit
findImportedModule will never return `HoleUnit` for a `ModuleName`
(a `HoleUnit` can only be found as a signature instantiation, never as a
directly *imported* thing)
Therefore, we can drop `[ModuleName]` returned by
`implicitRequirementsShallow`, which makes many things dead code.
Namely, the call to `implicitRequirementsShallow` from
GHC.Driver.Downsweep which was a performance bottleneck (for doing lots
of duplicate work in findImportedModule) is now entirely gone.
Fixes #27053
In an MR with this patch and the downsweep refactor (previous commit), CI says:
MultiComponentModules(normal) ghc/alloc 2,097,396,728 1,943,662,304 -7.3% GOOD
MultiComponentModules100(normal) ghc/alloc 24,310,182,136 17,227,574,440 -29.1% GOOD
MultiComponentModulesRecomp(normal) ghc/alloc 602,769,518 449,973,656 -25.3% GOOD
MultiComponentModulesRecomp100(normal) ghc/alloc 11,885,976,408 4,828,894,160 -59.4% GOOD
-------------------------
Metric Decrease:
MultiComponentModules
MultiComponentModules100
MultiComponentModulesRecomp
MultiComponentModulesRecomp100
-------------------------
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e032cb24
by Rodrigo Mesquita at 2026-08-15T02:49:34-04:00
downsweep: Cache negative results
When traversing a module graph structure, a uniquely identified node
should always expand to the same thing.
I don't see how visiting the same node which failed to be expanded a
first time would ever successfully expand the second time we try to
expand it (eg. when coming from a different edge to it -- it is still
the same node!). The node expansion is local, based just based on the
node itself, not on the path to get there.
Therefore, this patch removes the weird behavior and commentary of
`dfsBuild` wrt to `Nothing` not being cached and being potentially
expanded a second time around to something different, which was
misleading and, ultimately, incorrect.
Now, we have a `MGRes`, which is more explicit about a node being
Skipped just being a node that is ignored whenever it is found (and that
skip is cached) -- and we may want to do this due to failures or due to
just trying nodes which might not work on purpose, like hs-boots.
We uniformly cache positive and negative results and remove the
assumption that there might be an ordering in which the same node
visited at a later time might be expanded differently.
This makes it possible to traverse the module nodes in parallel without
a change in behavior, since there's no longer a hidden ordering
requirement.
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150fe3ff
by Rodrigo Mesquita at 2026-08-15T02:49:34-04:00
Organize and clean-up GHC.Driver.Downsweep
Simply some cosmetic changes, moving definitions around to structure the
module better into its relevant sections
(In go (ns ++ ss), it's not a problem to use ++ because it's a good
producer and we won't have to append fully before processing the next
item in go)
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dabe6ae8
by Wolfgang Jeltsch at 2026-08-15T02:49:35-04:00
Add support for textual output of bytecode file content
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9cff2f4d
by mangoiv at 2026-08-15T02:49:37-04:00
hadrian: set the executable bit for hie-bios.bat