[clang] [compiler-rt] [llvm] [SystemZ] Add support for half (fp16) (PR #109164)

[Jonas Paulsson via cfe-commits]

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@@ -6464,6 +6522,70 @@ static SDValue lowerAddrSpaceCast(SDValue Op, SelectionDAG &DAG) {
   return Op;
 }
 
+SDValue SystemZTargetLowering::lowerFP_EXTEND(SDValue Op,
+                                              SelectionDAG &DAG) const {
+  SDValue In = Op.getOperand(Op->isStrictFPOpcode() ? 1 : 0);
+  if (In.getSimpleValueType() != MVT::f16)
+    return Op;      // Legal
+  return SDValue(); // Let legalizer emit the libcall.
+}
+
+SDValue SystemZTargetLowering::lowerLoadF16(SDValue Op,
+                                            SelectionDAG &DAG) const {
+  MVT RegVT = Op.getSimpleValueType();
+  assert(RegVT == MVT::f16 && "Expected to lower an f16 load.");
+
+  SDLoc DL(Op);
+  SDValue NewLd;
+  if (auto *AtomicLd = dyn_cast<AtomicSDNode>(Op.getNode())) {
+    assert(EVT(RegVT) == AtomicLd->getMemoryVT() && "Unhandled f16 load");
+    NewLd = DAG.getAtomic(ISD::ATOMIC_LOAD, DL, MVT::i16, MVT::i32,
+                          AtomicLd->getChain(), AtomicLd->getBasePtr(),
+                          AtomicLd->getMemOperand());
+    cast<AtomicSDNode>(NewLd)->setExtensionType(ISD::EXTLOAD);
+  } else {
+    LoadSDNode *Ld = cast<LoadSDNode>(Op.getNode());
+    assert(EVT(RegVT) == Ld->getMemoryVT() && "Unhandled f16 load");
+    NewLd =
+        DAG.getExtLoad(ISD::EXTLOAD, DL, MVT::i32, Ld->getChain(),
+                       Ld->getBasePtr(), Ld->getPointerInfo(), MVT::i16,
+                       Ld->getOriginalAlign(), Ld->getMemOperand()->getFlags());
+  }
+  // Load as integer, shift and then insert into upper 2 bytes of the FP
+  // register.
+  SDValue Shft = DAG.getNode(ISD::SHL, DL, MVT::i32, NewLd,
+                             DAG.getConstant(16, DL, MVT::i32));
+  SDValue BCast = DAG.getNode(ISD::BITCAST, DL, MVT::f32, Shft);
+  SDValue F16Val =
+      DAG.getTargetExtractSubreg(SystemZ::subreg_h16, DL, MVT::f16, BCast);
----------------
JonPsson1 wrote:

Factoring out the actual conversions (insert/extract and shift) into separate functions.

With vector support, VL16 and VST16 have been added, and OperationAction for LOAD and STORE is then Legal, so this is never called. Adding comments for this now.


https://github.com/llvm/llvm-project/pull/109164