DAG: Implement softening for fp atomic store (#90840)

This will prevent SystemZ test regressions in a future change, tested by
#90826

Author: arsenm

llvm/lib/CodeGen/SelectionDAG/LegalizeFloatTypes.cpp

@@ -946,6 +946,9 @@ bool DAGTypeLegalizer::SoftenFloatOperand(SDNode *N, unsigned OpNo) {
   case ISD::STRICT_FSETCCS:
   case ISD::SETCC:       Res = SoftenFloatOp_SETCC(N); break;
   case ISD::STORE:       Res = SoftenFloatOp_STORE(N, OpNo); break;
+  case ISD::ATOMIC_STORE:
+    Res = SoftenFloatOp_ATOMIC_STORE(N, OpNo);
+    break;
   case ISD::FCOPYSIGN:   Res = SoftenFloatOp_FCOPYSIGN(N); break;
   }
 
@@ -1172,6 +1175,21 @@ SDValue DAGTypeLegalizer::SoftenFloatOp_STORE(SDNode *N, unsigned OpNo) {
                       ST->getMemOperand());
 }
 
+SDValue DAGTypeLegalizer::SoftenFloatOp_ATOMIC_STORE(SDNode *N, unsigned OpNo) {
+  assert(ISD::isUNINDEXEDStore(N) && "Indexed store during type legalization!");
+  assert(OpNo == 1 && "Can only soften the stored value!");
+  AtomicSDNode *ST = cast<AtomicSDNode>(N);
+  SDValue Val = ST->getVal();
+  EVT VT = Val.getValueType();
+  SDLoc dl(N);
+
+  assert(ST->getMemoryVT() == VT && "truncating atomic store not handled");
+
+  SDValue NewVal = GetSoftenedFloat(Val);
+  return DAG.getAtomic(ISD::ATOMIC_STORE, dl, VT, ST->getChain(), NewVal,
+                       ST->getBasePtr(), ST->getMemOperand());
+}
+
 SDValue DAGTypeLegalizer::SoftenFloatOp_FCOPYSIGN(SDNode *N) {
   SDValue LHS = N->getOperand(0);
   SDValue RHS = BitConvertToInteger(N->getOperand(1));

llvm/lib/CodeGen/SelectionDAG/LegalizeTypes.h

@@ -592,6 +592,7 @@ class LLVM_LIBRARY_VISIBILITY DAGTypeLegalizer {
   SDValue SoftenFloatOp_SELECT_CC(SDNode *N);
   SDValue SoftenFloatOp_SETCC(SDNode *N);
   SDValue SoftenFloatOp_STORE(SDNode *N, unsigned OpNo);
+  SDValue SoftenFloatOp_ATOMIC_STORE(SDNode *N, unsigned OpNo);
   SDValue SoftenFloatOp_FCOPYSIGN(SDNode *N);
 
   //===--------------------------------------------------------------------===//