[BPF] generate gotox only for cpuv4

Coincidentally this fixes two test failures:
- LLVM :: CodeGen/BPF/CORE/offset-reloc-fieldinfo-2-bpfeb.ll
- LLVM :: CodeGen/BPF/CORE/offset-reloc-fieldinfo-2.ll

These tests invoke llc with -mcpuv1 and have a switch statement in the
IR. Both tests failed with assertion in
SelectionDAGLegalize::LegalizeOp():

  for (const SDValue &Op : Node->op_values())
    assert((TLI.getTypeAction(*DAG.getContext(), Op.getValueType()) ==
              TargetLowering::TypeLegal ||
            Op.getOpcode() == ISD::TargetConstant ||
            Op.getOpcode() == ISD::Register) &&
            "Unexpected illegal type!");

At the moment of the failure:

  Op.getOpcode() == BPFISD::BPF_BR_JT

The error happened because one of the BPFBrJt parameters has i32 type:

  def SDT_BPFBrJt         : SDTypeProfile<0, 2, [SDTCisVT<0, i32>,    // jump table
                                                 SDTCisVT<1, i64>]>;  // index
  def BPFBrJt         : SDNode<"BPFISD::BPF_BR_JT", SDT_BPFBrJt,
                               [SDNPHasChain]>;

Author: eddyz87

llvm/lib/Target/BPF/BPFISelLowering.cpp

@@ -72,8 +72,10 @@ BPFTargetLowering::BPFTargetLowering(const TargetMachine &TM,
   setStackPointerRegisterToSaveRestore(BPF::R11);
 
   setOperationAction(ISD::BR_CC, MVT::i64, Custom);
-  setOperationAction(ISD::BR_JT, MVT::Other, Custom);
   setOperationAction(ISD::BRCOND, MVT::Other, Expand);
+  LegalizeAction IndirectBrAction = STI.hasGotox() ? Custom : Expand;
+  setOperationAction(ISD::BR_JT, MVT::Other, IndirectBrAction);
+  setOperationAction(ISD::BRIND, MVT::Other, IndirectBrAction);
 
   setOperationAction(ISD::TRAP, MVT::Other, Custom);
 

llvm/lib/Target/BPF/BPFSubtarget.cpp

@@ -43,6 +43,8 @@ static cl::opt<bool>
 static cl::opt<bool> Disable_load_acq_store_rel(
     "disable-load-acq-store-rel", cl::Hidden, cl::init(false),
     cl::desc("Disable load-acquire and store-release insns"));
+static cl::opt<bool> Disable_gotox("disable-gotox", cl::Hidden, cl::init(false),
+                                   cl::desc("Disable gotox insn"));
 
 void BPFSubtarget::anchor() {}
 
@@ -66,6 +68,7 @@ void BPFSubtarget::initializeEnvironment() {
   HasGotol = false;
   HasStoreImm = false;
   HasLoadAcqStoreRel = false;
+  HasGotox = false;
 }
 
 void BPFSubtarget::initSubtargetFeatures(StringRef CPU, StringRef FS) {
@@ -96,6 +99,7 @@ void BPFSubtarget::initSubtargetFeatures(StringRef CPU, StringRef FS) {
     HasGotol = !Disable_gotol;
     HasStoreImm = !Disable_StoreImm;
     HasLoadAcqStoreRel = !Disable_load_acq_store_rel;
+    HasGotox = !Disable_gotox;
     return;
   }
 }

llvm/lib/Target/BPF/BPFSubtarget.h

@@ -65,7 +65,7 @@ class BPFSubtarget : public BPFGenSubtargetInfo {
 
   // whether cpu v4 insns are enabled.
   bool HasLdsx, HasMovsx, HasBswap, HasSdivSmod, HasGotol, HasStoreImm,
-      HasLoadAcqStoreRel;
+      HasLoadAcqStoreRel, HasGotox;
 
   std::unique_ptr<CallLowering> CallLoweringInfo;
   std::unique_ptr<InstructionSelector> InstSelector;
@@ -94,6 +94,7 @@ class BPFSubtarget : public BPFGenSubtargetInfo {
   bool hasGotol() const { return HasGotol; }
   bool hasStoreImm() const { return HasStoreImm; }
   bool hasLoadAcqStoreRel() const { return HasLoadAcqStoreRel; }
+  bool hasGotox() const { return HasGotox; }
 
   bool isLittleEndian() const { return IsLittleEndian; }