[llvm] [WebAssembly] Enable simd128 when relaxed-simd is set in AsmPrinter (PR #99803)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-backend-webassembly

Author: Heejin Ahn (aheejin)

<details>
<summary>Changes</summary>

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` there 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.

---
Full diff: https://github.com/llvm/llvm-project/pull/99803.diff


2 Files Affected:

- (modified) llvm/lib/Target/WebAssembly/WebAssemblyInstrInfo.td (+1-1) 
- (added) llvm/test/CodeGen/WebAssembly/simd-asm-pred.ll (+24) 


``````````diff
diff --git a/llvm/lib/Target/WebAssembly/WebAssemblyInstrInfo.td b/llvm/lib/Target/WebAssembly/WebAssemblyInstrInfo.td
index 3d37eb2fa27bc..bb36ce7650183 100644
--- a/llvm/lib/Target/WebAssembly/WebAssemblyInstrInfo.td
+++ b/llvm/lib/Target/WebAssembly/WebAssemblyInstrInfo.td
@@ -78,7 +78,7 @@ def HasSignExt :
 
 def HasSIMD128 :
     Predicate<"Subtarget->hasSIMD128()">,
-    AssemblerPredicate<(all_of FeatureSIMD128), "simd128">;
+    AssemblerPredicate<(any_of FeatureSIMD128, FeatureRelaxedSIMD), "simd128">;
 
 def HasTailCall :
     Predicate<"Subtarget->hasTailCall()">,
diff --git a/llvm/test/CodeGen/WebAssembly/simd-asm-pred.ll b/llvm/test/CodeGen/WebAssembly/simd-asm-pred.ll
new file mode 100644
index 0000000000000..f022c3e745125
--- /dev/null
+++ b/llvm/test/CodeGen/WebAssembly/simd-asm-pred.ll
@@ -0,0 +1,24 @@
+; RUN: llc < %s -verify-machineinstrs -mattr=+relaxed-simd | FileCheck %s
+
+; Test that setting "relaxed-simd" target feature set also implies 'simd128' in
+; AssemblerPredicate, which is used to verify instructions in AsmPrinter.
+
+target triple = "wasm32-unknown-unknown"
+
+declare <2 x i64> @llvm.wasm.relaxed.laneselect.v2i64(<2 x i64>, <2 x i64>, <2 x i64>)
+
+; The compiled result of this function uses LOCAL_GET_V128, which is predicated
+; on the 'simd128' feature. We should be able to compile this when only
+; 'relaxed-simd' is set, which implies 'simd128'.
+define <2 x i64> @test(<2 x i64>, <2 x i64>, <2 x i64>) #0 {
+; CHECK-LABEL: test:
+; CHECK:         .functype  test (v128, v128, v128) -> (v128)
+; CHECK-NEXT:  # %bb.0:
+; CHECK-NEXT:    local.get  0
+; CHECK-NEXT:    local.get  1
+; CHECK-NEXT:    local.get  2
+; CHECK-NEXT:    i64x2.relaxed_laneselect
+start:
+  %_4 = tail call <2 x i64> @llvm.wasm.relaxed.laneselect.v2i64(<2 x i64> %0, <2 x i64> %1, <2 x i64> %2) #3
+  ret <2 x i64> %_4
+}

``````````

</details>


https://github.com/llvm/llvm-project/pull/99803