[Git][ghc/ghc][wip/romes/12935] 6 commits: determinism: Sampling uniques in the CG

Wed Sep 11 13:50:22 UTC 2024

Rodrigo Mesquita pushed to branch wip/romes/12935 at Glasgow Haskell Compiler / GHC

Commits:
6388e22f by Rodrigo Mesquita at 2024-09-11T14:49:19+01:00
determinism: Sampling uniques in the CG

To achieve object determinism, the passes processing Cmm and the rest of
the code generation pipeline musn't create new uniques which are
non-deterministic.

This commit changes occurrences of non-deterministic unique sampling
within these code generation passes by a deterministic unique sampling
strategy by propagating and threading through a deterministic
incrementing counter in them. The threading is done implicitly with
`UniqDSM` and `UniqDSMT`.

Secondly, the `DUniqSupply` used to run a `UniqDSM` must be threaded
through all passes to guarantee uniques in different passes are unique
amongst them altogether. Specifically, the same `DUniqSupply` must be
threaded through the CG Streaming pipeline, starting with Driver.Main
calling `StgToCmm.codeGen`, `cmmPipeline`, `cmmToRawCmm`, and
`codeOutput` in sequence.

To thread resources through the `Stream` abstraction, we use the `UniqDSMT`
transformer on top of `IO` as the Monad underlying the Stream. `UniqDSMT` will
thread the `DUniqSupply` through every pass applied to the `Stream`, for every
element. We use @type CgStream = Stream (UniqDSMT IO)@ for the Stream used in
code generation which that carries through the deterministic unique supply.

See Note [Deterministic Uniques in the CG]

- - - - -
c8fced61 by Rodrigo Mesquita at 2024-09-11T14:50:02+01:00
determinism: Cmm unique renaming pass

To achieve object determinism, we need to prevent the non-deterministic
uniques from leaking into the object code. We can do this by
deterministically renaming the non-external uniques in the Cmm groups
that are yielded right after StgToCmm.

The key to deterministic renaming is observing that the order of
declarations, instructions, and data in the Cmm groups are already
deterministic (modulo other determinism bugs), regardless of the
uniques. We traverse the Cmm AST in this deterministic order and
rename the uniques, incrementally, in the order they are found, thus
making them deterministic. This renaming is guarded by
-fobject-determinism which is disabled by default for now.

This is one of the key passes for object determinism. Read about the
overview of object determinism and a more detailed explanation of this
pass in:
* Note [Object determinism]
* Note [Renaming uniques deterministically]

Significantly closes the gap to #12935

- - - - -
119f0061 by Rodrigo Mesquita at 2024-09-11T14:50:02+01:00
determinism: DCmmGroup vs CmmGroup

Part of our strategy in producing deterministic objects, namely,
renaming all Cmm uniques in order, depend on the object code produced
having a deterministic order (say, A_closure always comes before
B_closure).

However, the use of LabelMaps in the Cmm representation invalidated this
requirement because the LabelMaps elements would already be in a
non-deterministic order (due to the original uniques), and the renaming
in sequence wouldn't work because of that non-deterministic order.

Therefore, we now start off with lists in CmmGroup (which preserve the
original order), and convert them into LabelMaps (for performance in the
code generator) after the uniques of the list elements have been
renamed.

See Note [DCmmGroup vs CmmGroup or: Deterministic Info Tables] and #12935.

- - - - -
f1b5d059 by Rodrigo Mesquita at 2024-09-11T14:50:02+01:00
determinism: Don't print unique in pprFullName

This unique was leaking as part of the profiling description in info
tables when profiling was enabled, despite not providing information
relevant to the profile.

- - - - -
254db8c3 by Rodrigo Mesquita at 2024-09-11T14:50:02+01:00
determinism: UDFM for distinct-constructor-tables

In order to produce deterministic objects when compiling with
-distinct-constructor-tables, we also have to update the data
constructor map to be backed by a deterministic unique map (UDFM) rather
than a non-deterministic one (UniqMap).

- - - - -
c4eea906 by Rodrigo Mesquita at 2024-09-11T14:50:02+01:00
determinism: Rename CmmGroups in generateCgIPEStub

Make sure to also deterministically rename the IPE Cmm (as per Note
[Renaming uniques deterministically]) to guarantee deterministic objects
when IPE information is requested.

- - - - -

30 changed files:

- compiler/GHC/Cmm.hs
- compiler/GHC/Cmm/BlockId.hs
- compiler/GHC/Cmm/CLabel.hs
- compiler/GHC/Cmm/Dataflow.hs
- compiler/GHC/Cmm/Dataflow/Graph.hs
- compiler/GHC/Cmm/Graph.hs
- compiler/GHC/Cmm/Info.hs
- compiler/GHC/Cmm/Info/Build.hs
- compiler/GHC/Cmm/LayoutStack.hs
- compiler/GHC/Cmm/Opt.hs
- compiler/GHC/Cmm/Parser.y
- compiler/GHC/Cmm/Pipeline.hs
- compiler/GHC/Cmm/ProcPoint.hs
- compiler/GHC/Cmm/Reducibility.hs
- compiler/GHC/Cmm/Sink.hs
- compiler/GHC/Cmm/Switch.hs
- compiler/GHC/Cmm/Switch/Implement.hs
- compiler/GHC/Cmm/ThreadSanitizer.hs
- + compiler/GHC/Cmm/UniqueRenamer.hs
- compiler/GHC/CmmToAsm.hs
- compiler/GHC/CmmToAsm/AArch64/CodeGen.hs
- compiler/GHC/CmmToAsm/AArch64/Instr.hs
- compiler/GHC/CmmToAsm/BlockLayout.hs
- compiler/GHC/CmmToAsm/Dwarf.hs
- compiler/GHC/CmmToAsm/Monad.hs
- compiler/GHC/CmmToAsm/PPC/Instr.hs
- compiler/GHC/CmmToAsm/Reg/Graph.hs
- compiler/GHC/CmmToAsm/Reg/Graph/Spill.hs
- compiler/GHC/CmmToAsm/Reg/Linear.hs
- compiler/GHC/CmmToAsm/Reg/Linear/Base.hs

The diff was not included because it is too large.

View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/compare/3b1a97f53b07fc0bd2642ec46a9ae0f9ee8185c1...c4eea9067c5cce38f6875efd7f6a1ba2ef71b362

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View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/compare/3b1a97f53b07fc0bd2642ec46a9ae0f9ee8185c1...c4eea9067c5cce38f6875efd7f6a1ba2ef71b362
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