Revert "[BPF] Allow libcalls behind a feature gate (llvm#168442)" (llvm#169733)

**Problem**

As mentioned in
llvm#168442 (review)
llvm#168442, is not the right solution for the problem.

I'll follow @arsenm suggestions starting with
llvm#169537 to properly allow safe
math operations and i128 support in BPF.

**Solution**

Revert llvm#168442.

Author: LucasSte

llvm/lib/Target/BPF/BPF.td

@@ -34,10 +34,6 @@ def MisalignedMemAccess : SubtargetFeature<"allows-misaligned-mem-access",
                                            "AllowsMisalignedMemAccess", "true",
                                            "Allows misaligned memory access">;
 
-def AllowBuiltinCall : SubtargetFeature<"allow-builtin-calls",
-                                        "AllowBuiltinCalls", "true",
-                                        "Allow calls to builtin functions">;
-
 def : Proc<"generic", []>;
 def : Proc<"v1", []>;
 def : Proc<"v2", []>;

llvm/lib/Target/BPF/BPFISelLowering.cpp

@@ -208,7 +208,6 @@ BPFTargetLowering::BPFTargetLowering(const TargetMachine &TM,
   HasMovsx = STI.hasMovsx();
 
   AllowsMisalignedMemAccess = STI.getAllowsMisalignedMemAccess();
-  AllowBuiltinCalls = STI.getAllowBuiltinCalls();
 }
 
 bool BPFTargetLowering::allowsMisalignedMemoryAccesses(EVT VT, unsigned, Align,
@@ -568,10 +567,9 @@ SDValue BPFTargetLowering::LowerCall(TargetLowering::CallLoweringInfo &CLI,
   } else if (ExternalSymbolSDNode *E = dyn_cast<ExternalSymbolSDNode>(Callee)) {
     if (StringRef(E->getSymbol()) != BPF_TRAP) {
       Callee = DAG.getTargetExternalSymbol(E->getSymbol(), PtrVT, 0);
-      if (!AllowBuiltinCalls)
-        fail(CLI.DL, DAG,
-             Twine("A call to built-in function '" + StringRef(E->getSymbol()) +
-                   "' is not supported."));
+      fail(CLI.DL, DAG,
+           Twine("A call to built-in function '" + StringRef(E->getSymbol()) +
+                 "' is not supported."));
     }
   }
 
@@ -1198,18 +1196,3 @@ bool BPFTargetLowering::isLegalAddressingMode(const DataLayout &DL,
 
   return true;
 }
-
-bool BPFTargetLowering::shouldSignExtendTypeInLibCall(Type *Ty,
-                                                      bool IsSigned) const {
-  return IsSigned || Ty->isIntegerTy(32);
-}
-
-bool BPFTargetLowering::CanLowerReturn(
-    CallingConv::ID CallConv, MachineFunction &MF, bool IsVarArg,
-    const SmallVectorImpl<ISD::OutputArg> &Outs, LLVMContext &Context,
-    const Type *RetTy) const {
-  // At minimal return Outs.size() <= 1, or check valid types in CC.
-  SmallVector<CCValAssign, 16> RVLocs;
-  CCState CCInfo(CallConv, IsVarArg, MF, RVLocs, Context);
-  return CCInfo.CheckReturn(Outs, getHasAlu32() ? RetCC_BPF32 : RetCC_BPF64);
-}

llvm/lib/Target/BPF/BPFISelLowering.h

@@ -68,8 +68,6 @@ class BPFTargetLowering : public TargetLowering {
   // Allows Misalignment
   bool AllowsMisalignedMemAccess;
 
-  bool AllowBuiltinCalls;
-
   SDValue LowerSDIVSREM(SDValue Op, SelectionDAG &DAG) const;
   SDValue LowerDYNAMIC_STACKALLOC(SDValue Op, SelectionDAG &DAG) const;
   SDValue LowerBR_CC(SDValue Op, SelectionDAG &DAG) const;
@@ -165,14 +163,6 @@ class BPFTargetLowering : public TargetLowering {
   MachineBasicBlock *
   EmitInstrWithCustomInserterLDimm64(MachineInstr &MI,
                                      MachineBasicBlock *BB) const;
-
-  // Returns true if arguments should be sign-extended in lib calls.
-  bool shouldSignExtendTypeInLibCall(Type *Ty, bool IsSigned) const override;
-
-  bool CanLowerReturn(CallingConv::ID CallConv, MachineFunction &MF,
-                      bool IsVarArg,
-                      const SmallVectorImpl<ISD::OutputArg> &Outs,
-                      LLVMContext &Context, const Type *RetTy) const override;
 };
 }
 

llvm/lib/Target/BPF/BPFSubtarget.cpp

@@ -70,7 +70,6 @@ void BPFSubtarget::initializeEnvironment() {
   HasLoadAcqStoreRel = false;
   HasGotox = false;
   AllowsMisalignedMemAccess = false;
-  AllowBuiltinCalls = false;
 }
 
 void BPFSubtarget::initSubtargetFeatures(StringRef CPU, StringRef FS) {

llvm/lib/Target/BPF/BPFSubtarget.h

@@ -70,8 +70,6 @@ class BPFSubtarget : public BPFGenSubtargetInfo {
   bool HasLdsx, HasMovsx, HasBswap, HasSdivSmod, HasGotol, HasStoreImm,
       HasLoadAcqStoreRel, HasGotox;
 
-  bool AllowBuiltinCalls;
-
   std::unique_ptr<CallLowering> CallLoweringInfo;
   std::unique_ptr<InstructionSelector> InstSelector;
   std::unique_ptr<LegalizerInfo> Legalizer;
@@ -103,7 +101,6 @@ class BPFSubtarget : public BPFGenSubtargetInfo {
   bool hasStoreImm() const { return HasStoreImm; }
   bool hasLoadAcqStoreRel() const { return HasLoadAcqStoreRel; }
   bool hasGotox() const { return HasGotox; }
-  bool getAllowBuiltinCalls() const { return AllowBuiltinCalls; }
 
   bool isLittleEndian() const { return IsLittleEndian; }
 

llvm/test/CodeGen/BPF/atomic-oversize.ll

@@ -1,4 +1,6 @@
 ; RUN: llc -mtriple=bpf < %s | FileCheck %s
+; XFAIL: *
+; Doesn't currently build, with error 'only small returns supported'.
 
 define void @test(ptr %a) nounwind {
 ; CHECK-LABEL: test:

llvm/test/CodeGen/BPF/builtin_calls.ll

@@ -1,6 +1,6 @@
 ; RUN: not llc -mtriple=bpf < %s 2> %t1
 ; RUN: FileCheck %s < %t1
-; CHECK: error: <unknown>:0:0: in function bar { i64, i32 } (i32, i32, i32, i32, i32): stack arguments are not supported
+; CHECK: error: <unknown>:0:0: in function bar { i64, i32 } (i32, i32, i32, i32, i32): aggregate returns are not supported
 
 %struct.S = type { i32, i32, i32 }
 

llvm/test/CodeGen/BPF/struct_ret1.ll

@@ -1,6 +1,6 @@
 ; RUN: not llc -mtriple=bpf < %s 2> %t1
 ; RUN: FileCheck %s < %t1
-; CHECK: too many arguments
+; CHECK: only small returns
 
 ; Function Attrs: nounwind uwtable
 define { i64, i32 } @foo(i32 %a, i32 %b, i32 %c) #0 {