[SelectionDAG] Remove `UnsafeFPMath` in LegalizeDAG (#146316)

These global flags hinder further improvements like [[RFC] Honor pragmas
with
-ffp-contract=fast](https://discourse.llvm.org/t/rfc-honor-pragmas-with-ffp-contract-fast)
and pass concurrency support. Remove them incrementally.

1 files changed, 5 insertions, 1 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
index 1636465..6eca7b7 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
@@ -3923,11 +3923,15 @@ void SelectionDAGBuilder::visitFPTrunc(const User &I) {
   // FPTrunc is never a no-op cast, no need to check
   SDValue N = getValue(I.getOperand(0));
   SDLoc dl = getCurSDLoc();
+  SDNodeFlags Flags;
+  if (auto *TruncInst = dyn_cast<FPMathOperator>(&I))
+    Flags.copyFMF(*TruncInst);
   const TargetLowering &TLI = DAG.getTargetLoweringInfo();
   EVT DestVT = TLI.getValueType(DAG.getDataLayout(), I.getType());
   setValue(&I, DAG.getNode(ISD::FP_ROUND, dl, DestVT, N,
                            DAG.getTargetConstant(
-                               0, dl, TLI.getPointerTy(DAG.getDataLayout()))));
+                               0, dl, TLI.getPointerTy(DAG.getDataLayout())),
+                           Flags));
 }
 
 void SelectionDAGBuilder::visitFPExt(const User &I) {