[all-commits] [llvm/llvm-project] a22ffe: [WebAssembly] Make RefTypeMem2Local recognize targ...

[Heejin Ahn via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: a22ffe54a33035d95ee239a11b4dc771f66d102b
      https://github.com/llvm/llvm-project/commit/a22ffe54a33035d95ee239a11b4dc771f66d102b
  Author: Heejin Ahn <aheejin at gmail.com>
  Date:   2024-04-23 (Tue, 23 Apr 2024)

  Changed paths:
    M llvm/lib/Target/WebAssembly/WebAssemblyRefTypeMem2Local.cpp
    M llvm/lib/Target/WebAssembly/WebAssemblyTargetMachine.cpp
    M llvm/test/CodeGen/WebAssembly/ref-type-mem2local.ll

  Log Message:
  -----------
  [WebAssembly] Make RefTypeMem2Local recognize target-features (#88916)

Currently we check `Subtarget->hasReferenceTypes()` to decide whether to
run `RefTypeMem2Local` pass:

https://github.com/llvm/llvm-project/blob/6133878227efc30355c02c2f089e06ce58231a3d/llvm/lib/Target/WebAssembly/WebAssemblyTargetMachine.cpp#L491-L495

This works fine when `-mattr=+reference-types` is given in the command
line (of `llc` or of `wasm-ld` in case of LTO). This also works fine if
the backend is called by Clang, because Clang's feature set will be
passed to the backend when creating a `TargetMachine`:
https://github.com/llvm/llvm-project/blob/ac791888bbbe58651e597cf7a4b2276424b77a92/clang/lib/CodeGen/BackendUtil.cpp#L549-L550
https://github.com/llvm/llvm-project/blob/ac791888bbbe58651e597cf7a4b2276424b77a92/clang/lib/CodeGen/BackendUtil.cpp#L561-L562

But if the backend compilation is called by `llc`, a `TargetMachine` is
created here:

https://github.com/llvm/llvm-project/blob/bf1ad1d267b1f911cb9846403d2c3d3250a40870/llvm/tools/llc/llc.cpp#L554-L555
And if the backend is called by `wasm-ld`'s LTO, a `TargetMachine` is
created here:

https://github.com/llvm/llvm-project/blob/ac791888bbbe58651e597cf7a4b2276424b77a92/llvm/lib/LTO/LTOBackend.cpp#L513
At this point, in the both places, the created `TargetMachine` only has
access to target features given by the command line with `-mattr=` and
doesn't have access to bitcode functions' `target-features` attribute.

We later gather the target features used by functions and store that
info in the `TargetMachine` in `CoalesceFeaturesAndStripAtomics`,
https://github.com/llvm/llvm-project/blob/ac791888bbbe58651e597cf7a4b2276424b77a92/llvm/lib/Target/WebAssembly/WebAssemblyTargetMachine.cpp#L202-L206
but this runs in the pass pipeline driven by the pass manager, so this
has not run by the time we check `Subtarget->hasReferenceTypes()` in
`WebAssemblyPassConfig::addISelPrepare`. So currently `RefTypeMem2Local`
would not run on those functions with
`"target-features"="+reference-types"` attributes if the backend is
called by `llc` or `wasm-ld`.

So this makes `RefTypeMem2Local` pass run unconditionally, and checks
`target-featurs` function attribute to decide whether to run the pass on
each function. This allows the pass to run with `wasm-ld` + LTO and
`llc`, even if `-mattr=+reference-types` is not explicitly given in the
command line again, as long as `+reference-types` is in the function's
`target-features` attribute.

This also covers the case we give the target features by the command
line like `llc -mattr=+reference-types` and not in the bitcode
function's attribute, because attributes given in the command line will
be stored in the function's attributes anyway:

https://github.com/llvm/llvm-project/blob/bd28889732e14ac6baca686c3ec99a82fc9cd89d/llvm/lib/CodeGen/CommandFlags.cpp#L673-L674
https://github.com/llvm/llvm-project/blob/bd28889732e14ac6baca686c3ec99a82fc9cd89d/llvm/lib/CodeGen/CommandFlags.cpp#L732-L733

With this PR,
- `lto0.test_externref_emjs`
- `thinlto0.test_externref_emjs`,
- `lto0.test_externref_emjs_dynlink`,
- `thinlto0.test_externref_emjs_dynlnk`

pass. These currently fail but don't get checked in the CI. I think they
used to pass but started to fail after #83196, because we used to run
mem2reg even with `-O0` before that.
(`ltoN` (N > 0) tests are not affected because they run mem2reg anyway
so they don't need `RefTypeMem2Local`)



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