[all-commits] [llvm/llvm-project] 735852: [WebAssembly] Enable simd128 when relaxed-simd is ...

[Heejin Ahn via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 735852f5ab9ad8872ded8d6815f309cdec680b1e
      https://github.com/llvm/llvm-project/commit/735852f5ab9ad8872ded8d6815f309cdec680b1e
  Author: Heejin Ahn <aheejin at gmail.com>
  Date:   2024-07-23 (Tue, 23 Jul 2024)

  Changed paths:
    M llvm/lib/Target/WebAssembly/WebAssemblyInstrInfo.td
    A llvm/test/CodeGen/WebAssembly/simd-asm-pred.ll

  Log Message:
  -----------
  [WebAssembly] Enable simd128 when relaxed-simd is set in AsmPrinter (#99803)

Even though in `Subtarget` we defined `SIMDLevel` as a number so
`hasRelaxedSIMD` automatically means `hasSIMD128`,
https://github.com/llvm/llvm-project/blob/0caf0c93e759816663af52e8632d1c3953dbc715/llvm/lib/Target/WebAssembly/WebAssemblySubtarget.h#L36-L40
https://github.com/llvm/llvm-project/blob/0caf0c93e759816663af52e8632d1c3953dbc715/llvm/lib/Target/WebAssembly/WebAssemblySubtarget.h#L107

specifying only `relaxed-simd` feature on a program that needs `simd128`
instructions to compile fails, because of this query in `AsmPrinter`:
https://github.com/llvm/llvm-project/blob/d0d05aec3b6792136a9f75eb85dd2ea66005ae12/llvm/lib/Target/WebAssembly/WebAssemblyAsmPrinter.cpp#L644-L645

This `verifyInstructionPredicates` function (and other functions called
by this function) is generated by

https://github.com/llvm/llvm-project/blob/main/llvm/utils/TableGen/InstrInfoEmitter.cpp,
and looks like this (you can check it in the
`lib/Target/WebAssembly/WebAssemblyGenInstrInfo.inc` in your build
directory):
```cpp
void verifyInstructionPredicates(
    unsigned Opcode, const FeatureBitset &Features) {
  FeatureBitset AvailableFeatures = computeAvailableFeatures(Features);
  FeatureBitset RequiredFeatures = computeRequiredFeatures(Opcode);
  FeatureBitset MissingFeatures =
      (AvailableFeatures & RequiredFeatures) ^
      RequiredFeatures;
  ...
}
```

And `computeAvailableFeatures` is just a set query, like this:
```cpp
inline FeatureBitset computeAvailableFeatures(const FeatureBitset &FB) {
  FeatureBitset Features;
  if (FB[WebAssembly::FeatureAtomics])
    Features.set(Feature_HasAtomicsBit);
  if (FB[WebAssembly::FeatureBulkMemory])
    Features.set(Feature_HasBulkMemoryBit);
  if (FB[WebAssembly::FeatureExceptionHandling])
    Features.set(Feature_HasExceptionHandlingBit);
  ...
```

So this is how currently `HasSIMD128` is defined:

https://github.com/llvm/llvm-project/blob/0caf0c93e759816663af52e8632d1c3953dbc715/llvm/lib/Target/WebAssembly/WebAssemblyInstrInfo.td#L79-L81

The things being checked in this `computeAvailableFeatures`, and in turn
in `AsmPrinter`, are `AssemblerPredicate`s. These only check which bits
are set in the features set and are different from `Predicate`s, which
can call `Subtarget` functions like `Subtarget->hasSIMD128()`.

But apparently we can use `all_of` and `any_of` directives in
`AssemblerPredicate`, and we can make `simd128`'s `AssemblerPredicate`
set in `relaxed-simd` is set by the condition as an 'or' of the two.

Fixes #98502.



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