[llvm] relaxed simd fma (PR #147487)

[Matt Arsenault via llvm-commits]

================
@@ -3412,6 +3418,37 @@ static SDValue performSETCCCombine(SDNode *N,
   return SDValue();
 }
 
+static SDValue performFAddCombine(SDNode *N, SelectionDAG &DAG) {
+  assert(N->getOpcode() == ISD::FADD);
+  using namespace llvm::SDPatternMatch;
+  if (!N->getFlags().hasFastMath())
+    return SDValue();
+
+  SDLoc DL(N);
+  SDValue A, B, C;
+  EVT VecVT = N->getValueType(0);
+  if (sd_match(N, m_FAdd(m_Value(A), m_FMul(m_Value(B), m_Value(C)))))
+    return DAG.getNode(
+        ISD::INTRINSIC_WO_CHAIN, DL, VecVT,
+        {DAG.getConstant(Intrinsic::wasm_relaxed_madd, DL, MVT::i32), A, B, C});
+
+  return SDValue();
+}
+
+static SDValue performFMACombine(SDNode *N, SelectionDAG &DAG) {
+  assert(N->getOpcode() == ISD::FMA);
+  if (!N->getFlags().hasFastMath())
+    return SDValue();
+
+  SDLoc DL(N);
+  SDValue A = N->getOperand(0), B = N->getOperand(1), C = N->getOperand(2);
+  EVT VecVT = N->getValueType(0);
+
+  return DAG.getNode(
+      ISD::INTRINSIC_WO_CHAIN, DL, VecVT,
+      {DAG.getConstant(Intrinsic::wasm_relaxed_madd, DL, MVT::i32), A, B, C});
+}
----------------
arsenm wrote:

I doubt it's appropriate to turn an FMA into a not-FMA, regardless of fast math flags. What are the semantics of wasm_relaxed_madd?

https://github.com/llvm/llvm-project/pull/147487