[PATCH] D55897: Add constrained fptrunc and fpext intrinsics

[Craig Topper via Phabricator via llvm-commits]

craig.topper added inline comments.


================
Comment at: lib/CodeGen/SelectionDAG/LegalizeVectorTypes.cpp:3058
+      Ops[0] = InOp;
+      SDValue InVec = DAG.getNode(ISD::CONCAT_VECTORS, DL, InWidenVT, Ops);
+
----------------
kpn wrote:
> craig.topper wrote:
> > We can't really widen this can we? Won't that put garbage in the upper elements?
> Is that what getUNDEF() does? Give llvm license to put garbage in registers? My assumption is that the code is fine because this function is a copy of WidenVecRes_Convert() with the needed changes for the strict node being chained. If if there's a problem here there's also a problem in that function.
That is what the undef means. The existing code isn't required to be exception safe so garbage is fine. The constrained intrinsics have to be exception safe. This is why the implementation of WidenVecRes_StrictFP is different than the non-trapping case in WidenVecRes_BinaryCanTrap. I believe FADD/FSUB/FDIV/FMUL are considered non-trapping on most targets.


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D55897/new/

https://reviews.llvm.org/D55897