[LoongArch] Don't crash on instruction prefetch intrinsics (#135760)

Instead of failing to select during isel, drop the intrinsic in
lowering.

Similar as the X86's PR. Seeing: https://reviews.llvm.org/D151050.

Fixes #134624

Author: leecheechen

llvm/lib/Target/LoongArch/LoongArchISelLowering.cpp

@@ -99,7 +99,7 @@ LoongArchTargetLowering::LoongArchTargetLowering(const TargetMachine &TM,
   setOperationAction(ISD::INTRINSIC_W_CHAIN, MVT::Other, Custom);
   setOperationAction(ISD::INTRINSIC_WO_CHAIN, MVT::Other, Custom);
 
-  setOperationAction(ISD::PREFETCH, MVT::Other, Legal);
+  setOperationAction(ISD::PREFETCH, MVT::Other, Custom);
 
   // Expand bitreverse.i16 with native-width bitrev and shift for now, before
   // we get to know which of sll and revb.2h is faster.
@@ -469,10 +469,24 @@ SDValue LoongArchTargetLowering::LowerOperation(SDValue Op,
     return lowerBITREVERSE(Op, DAG);
   case ISD::SCALAR_TO_VECTOR:
     return lowerSCALAR_TO_VECTOR(Op, DAG);
+  case ISD::PREFETCH:
+    return lowerPREFETCH(Op, DAG);
   }
   return SDValue();
 }
 
+SDValue LoongArchTargetLowering::lowerPREFETCH(SDValue Op,
+                                               SelectionDAG &DAG) const {
+  unsigned IsData = Op.getConstantOperandVal(4);
+
+  // We don't support non-data prefetch.
+  // Just preserve the chain.
+  if (!IsData)
+    return Op.getOperand(0);
+
+  return Op;
+}
+
 SDValue
 LoongArchTargetLowering::lowerSCALAR_TO_VECTOR(SDValue Op,
                                                SelectionDAG &DAG) const {

llvm/lib/Target/LoongArch/LoongArchISelLowering.h

@@ -353,6 +353,7 @@ class LoongArchTargetLowering : public TargetLowering {
   SDValue lowerVECTOR_SHUFFLE(SDValue Op, SelectionDAG &DAG) const;
   SDValue lowerBITREVERSE(SDValue Op, SelectionDAG &DAG) const;
   SDValue lowerSCALAR_TO_VECTOR(SDValue Op, SelectionDAG &DAG) const;
+  SDValue lowerPREFETCH(SDValue Op, SelectionDAG &DAG) const;
 
   bool isFPImmLegal(const APFloat &Imm, EVT VT,
                     bool ForCodeSize) const override;

llvm/test/CodeGen/LoongArch/prefetchi.ll

@@ -0,0 +1,33 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 5
+; RUN: llc --mtriple=loongarch32 < %s | FileCheck %s --check-prefix=LA32
+; RUN: llc --mtriple=loongarch64 < %s | FileCheck %s --check-prefix=LA64
+
+declare void @llvm.prefetch(ptr, i32, i32, i32) nounwind
+
+define dso_local void @prefetch_no_offset(ptr %ptr) nounwind {
+; LA32-LABEL: prefetch_no_offset:
+; LA32:       # %bb.0: # %entry
+; LA32-NEXT:    ret
+;
+; LA64-LABEL: prefetch_no_offset:
+; LA64:       # %bb.0: # %entry
+; LA64-NEXT:    ret
+entry:
+  tail call void @llvm.prefetch(ptr %ptr, i32 0, i32 3, i32 0)
+  ret void
+}
+
+
+define dso_local void @prefetch_with_offset(ptr %ptr) nounwind {
+; LA32-LABEL: prefetch_with_offset:
+; LA32:       # %bb.0: # %entry
+; LA32-NEXT:    ret
+;
+; LA64-LABEL: prefetch_with_offset:
+; LA64:       # %bb.0: # %entry
+; LA64-NEXT:    ret
+entry:
+  %addr = getelementptr i8, ptr %ptr, i64 200
+  tail call void @llvm.prefetch(ptr %addr, i32 0, i32 3, i32 0)
+  ret void
+}