[WebAssembly] Constant fold wasm.dot (#149619)

Constant fold wasm.dot of constant vectors/splats.

Test case added in
`llvm/test/Transforms/InstSimplify/ConstProp/WebAssembly/dot.ll`

Related to https://github.com/llvm/llvm-project/issues/55933

1 files changed, 25 insertions, 0 deletions

diff --git a/llvm/lib/Analysis/ConstantFolding.cpp b/llvm/lib/Analysis/ConstantFolding.cpp
index dd98b62..4969528 100644
--- a/llvm/lib/Analysis/ConstantFolding.cpp
+++ b/llvm/lib/Analysis/ConstantFolding.cpp
@@ -1659,6 +1659,7 @@ bool llvm::canConstantFoldCallTo(const CallBase *Call, const Function *F) {
   case Intrinsic::aarch64_sve_convert_from_svbool:
   case Intrinsic::wasm_alltrue:
   case Intrinsic::wasm_anytrue:
+  case Intrinsic::wasm_dot:
   // WebAssembly float semantics are always known
   case Intrinsic::wasm_trunc_signed:
   case Intrinsic::wasm_trunc_unsigned:
@@ -3989,6 +3990,30 @@ static Constant *ConstantFoldFixedVectorCall(
     }
     return ConstantVector::get(Result);
   }
+  case Intrinsic::wasm_dot: {
+    unsigned NumElements =
+        cast<FixedVectorType>(Operands[0]->getType())->getNumElements();
+
+    assert(NumElements == 8 && Result.size() == 4 &&
+           "wasm dot takes i16x8 and produces i32x4");
+    assert(Ty->isIntegerTy());
+    int32_t MulVector[8];
+
+    for (unsigned I = 0; I < NumElements; ++I) {
+      ConstantInt *Elt0 =
+          cast<ConstantInt>(Operands[0]->getAggregateElement(I));
+      ConstantInt *Elt1 =
+          cast<ConstantInt>(Operands[1]->getAggregateElement(I));
+
+      MulVector[I] = Elt0->getSExtValue() * Elt1->getSExtValue();
+    }
+    for (unsigned I = 0; I < Result.size(); I++) {
+      int32_t IAdd = MulVector[I * 2] + MulVector[I * 2 + 1];
+      Result[I] = ConstantInt::get(Ty, IAdd);
+    }
+
+    return ConstantVector::get(Result);
+  }
   default:
     break;
   }