[BPF] Ensure GotoX only supported at CPU V4

This is temporary and it makes easy to run bpf selftests.
Once kernel side is ready, we will implement CPU V5 which
will support jump tables.

Author: Yonghong Song

llvm/lib/Target/BPF/BPFISelLowering.cpp

@@ -74,10 +74,14 @@ BPFTargetLowering::BPFTargetLowering(const TargetMachine &TM,
   setOperationAction(ISD::BR_JT, MVT::Other, Expand);
   setOperationAction(ISD::BRCOND, MVT::Other, Expand);
 
+  if (!STI.hasGotox())
+    setOperationAction(ISD::BRIND, MVT::Other, Expand);
+
   setOperationAction(ISD::TRAP, MVT::Other, Custom);
 
   setOperationAction({ISD::GlobalAddress, ISD::ConstantPool}, MVT::i64, Custom);
-  setOperationAction({ISD::JumpTable, ISD::BlockAddress}, MVT::i64, Custom);
+  if (STI.hasGotox())
+    setOperationAction({ISD::JumpTable, ISD::BlockAddress}, MVT::i64, Custom);
 
   setOperationAction(ISD::DYNAMIC_STACKALLOC, MVT::i64, Custom);
   setOperationAction(ISD::STACKSAVE, MVT::Other, Expand);

llvm/lib/Target/BPF/BPFInstrInfo.td

@@ -61,6 +61,7 @@ def BPFNoMovsx : Predicate<"!Subtarget->hasMovsx()">;
 def BPFNoBswap : Predicate<"!Subtarget->hasBswap()">;
 def BPFHasStoreImm : Predicate<"Subtarget->hasStoreImm()">;
 def BPFHasLoadAcqStoreRel : Predicate<"Subtarget->hasLoadAcqStoreRel()">;
+def BPFHasGotox : Predicate<"Subtarget->hasGotox()">;
 
 class ImmediateAsmOperand<string name> : AsmOperandClass {
   let Name = name;
@@ -294,8 +295,10 @@ defm JSLE : J<BPF_JSLE, "s<=", BPF_CC_LE, BPF_CC_LE_32>;
 defm JSET : J<BPF_JSET, "&", NoCond, NoCond>;
 def JCOND : JMP_JCOND<BPF_JCOND, "may_goto", []>;
 
-let isIndirectBranch = 1, isBarrier = 1 in {
-  def JX : JMP_IND<BPF_JA, "gotox", [(brind i64:$dst)]>;
+let Predicates = [BPFHasGotox] in {
+  let isIndirectBranch = 1, isBarrier = 1 in {
+    def JX : JMP_IND<BPF_JA, "gotox", [(brind i64:$dst)]>;
+  }
 }
 }
 

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; }