[RISCV] Add ISD::EH_DWARF_CFA

[sunshaoce]

Summary

Based on D24038.
LLVM has an @llvm.eh.dwarf.cfa intrinsic, used to lower the GCC-compatible __builtin_dwarf_cfa() builtin.

[StephenFan]

llvm/test/CodeGen/RISCV/eh-dwarf-cfa.ll

38

Inconsistent between comment and real code about nounwind attribute.

[sunshaoce]

Address comments.

[StephenFan]

llvm/lib/Target/RISCV/RISCVISelLowering.cpp

192

Would it be better to only lower i64 EH_DWARF_CFA in RV64? Because the result operand of EH_DWARF_CFA is pointer type and we can't represent an i64 pointer type in RV32.

[sunshaoce]

Address @StephenFan's comments.

[luismarques]

llvm/test/CodeGen/RISCV/eh-dwarf-cfa.ll

6

Nit: demangle the function names, to make the test more human-readable.

38

Remove the comment

[sunshaoce]

Address @luismarques's comments.

llvm/lib/Target/RISCV/RISCVISelLowering.h

private:
   SDValue lowerVPSetCCMaskOp(SDValue Op, SelectionDAG &DAG) const;
   SDValue lowerVPFPIntConvOp(SDValue Op, SelectionDAG &DAG,
                              unsigned RISCVISDOpc) const;
   SDValue lowerFixedLengthVectorExtendToRVV(SDValue Op, SelectionDAG &DAG,
                                             unsigned ExtendOpc) const;
   SDValue lowerGET_ROUNDING(SDValue Op, SelectionDAG &DAG) const;
   SDValue lowerSET_ROUNDING(SDValue Op, SelectionDAG &DAG) const;
 
+  SDValue lowerEH_DWARF_CFA(SDValue Op, SelectionDAG &DAG) const;
+
   SDValue expandUnalignedRVVLoad(SDValue Op, SelectionDAG &DAG) const;
   SDValue expandUnalignedRVVStore(SDValue Op, SelectionDAG &DAG) const;
 
   bool isEligibleForTailCallOptimization(
       CCState &CCInfo, CallLoweringInfo &CLI, MachineFunction &MF,
       const SmallVector<CCValAssign, 16> &ArgLocs) const;
 
   /// Generate error diagnostics if any register used by CC has been marked

llvm/lib/Target/RISCV/RISCVISelLowering.cpp

RISCVTargetLowering::RISCVTargetLowering(const TargetMachine &TM,
   setOperationAction(ISD::SELECT_CC, XLenVT, Expand);
 
   setOperationAction({ISD::STACKSAVE, ISD::STACKRESTORE}, MVT::Other, Expand);
 
   setOperationAction(ISD::VASTART, MVT::Other, Custom);
   setOperationAction({ISD::VAARG, ISD::VACOPY, ISD::VAEND}, MVT::Other, Expand);
 
   setOperationAction(ISD::SIGN_EXTEND_INREG, MVT::i1, Expand);
+
+  setOperationAction(ISD::EH_DWARF_CFA, MVT::i32, Custom);
+  setOperationAction(ISD::EH_DWARF_CFA, MVT::i64, Custom);
+
   if (!Subtarget.hasStdExtZbb())
     setOperationAction(ISD::SIGN_EXTEND_INREG, {MVT::i8, MVT::i16}, Expand);
 
   if (Subtarget.is64Bit()) {
     setOperationAction({ISD::ADD, ISD::SUB, ISD::SHL, ISD::SRA, ISD::SRL},
                        MVT::i32, Custom);
 
     setOperationAction({ISD::UADDO, ISD::USUBO, ISD::UADDSAT, ISD::USUBSAT},
case ISD::VP_GATHER:
     return lowerMaskedGather(Op, DAG);
   case ISD::MSCATTER:
   case ISD::VP_SCATTER:
     return lowerMaskedScatter(Op, DAG);
   case ISD::FLT_ROUNDS_:
     return lowerGET_ROUNDING(Op, DAG);
   case ISD::SET_ROUNDING:
     return lowerSET_ROUNDING(Op, DAG);
+  case ISD::EH_DWARF_CFA:
+    return lowerEH_DWARF_CFA(Op, DAG);
   case ISD::VP_SELECT:
     return lowerVPOp(Op, DAG, RISCVISD::VSELECT_VL);
   case ISD::VP_MERGE:
     return lowerVPOp(Op, DAG, RISCVISD::VP_MERGE_VL);
   case ISD::VP_ADD:
     return lowerVPOp(Op, DAG, RISCVISD::ADD_VL);
   case ISD::VP_SUB:
     return lowerVPOp(Op, DAG, RISCVISD::SUB_VL);
SDValue RISCVTargetLowering::lowerSET_ROUNDING(SDValue Op,
   SDValue Shifted = DAG.getNode(ISD::SRL, DL, XLenVT,
                                 DAG.getConstant(Table, DL, XLenVT), Shift);
   RMValue = DAG.getNode(ISD::AND, DL, XLenVT, Shifted,
                         DAG.getConstant(0x7, DL, XLenVT));
   return DAG.getNode(RISCVISD::WRITE_CSR, DL, MVT::Other, Chain, SysRegNo,
                      RMValue);
 }
 
+SDValue RISCVTargetLowering::lowerEH_DWARF_CFA(SDValue Op,
+                                               SelectionDAG &DAG) const {
+  // Return a fixed StackObject with offset 0 which points to the old stack
+  // pointer.
+  MachineFrameInfo &MFI = DAG.getMachineFunction().getFrameInfo();
+  EVT ValTy = Op->getValueType(0);
+  int FI = MFI.CreateFixedObject(Op.getValueSizeInBits() / 8, 0, false);
+  return DAG.getFrameIndex(FI, ValTy);
+}
+
 static RISCVISD::NodeType getRISCVWOpcodeByIntr(unsigned IntNo) {
   switch (IntNo) {
   default:
     llvm_unreachable("Unexpected Intrinsic");
   case Intrinsic::riscv_bcompress:
     return RISCVISD::BCOMPRESSW;
   case Intrinsic::riscv_bdecompress:
     return RISCVISD::BDECOMPRESSW;

llvm/test/CodeGen/RISCV/eh-dwarf-cfa.ll

+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc -mtriple=riscv32 < %s | FileCheck -check-prefix=RV32 %s
+; RUN: llc -mtriple=riscv64 < %s | FileCheck -check-prefix=RV64 %s
+
+define void @_Z1fv() {
+; RV32-LABEL: _Z1fv:
+; RV32:       # %bb.0: # %entry
+; RV32-NEXT:    addi sp, sp, -16
+; RV32-NEXT:    .cfi_def_cfa_offset 16
+; RV32-NEXT:    sw ra, 12(sp) # 4-byte Folded Spill
+; RV32-NEXT:    .cfi_offset ra, -4
+; RV32-NEXT:    addi a0, sp, 16
+; RV32-NEXT:    call _Z1gPv@plt
+; RV32-NEXT:    lw ra, 12(sp) # 4-byte Folded Reload
+; RV32-NEXT:    addi sp, sp, 16
+; RV32-NEXT:    ret
+;
+; RV64-LABEL: _Z1fv:
+; RV64:       # %bb.0: # %entry
+; RV64-NEXT:    addi sp, sp, -16
+; RV64-NEXT:    .cfi_def_cfa_offset 16
+; RV64-NEXT:    sd ra, 8(sp) # 8-byte Folded Spill
+; RV64-NEXT:    .cfi_offset ra, -8
+; RV64-NEXT:    addi a0, sp, 16
+; RV64-NEXT:    call _Z1gPv@plt
+; RV64-NEXT:    ld ra, 8(sp) # 8-byte Folded Reload
+; RV64-NEXT:    addi sp, sp, 16
+; RV64-NEXT:    ret
+entry:
+  %0 = call i8* @llvm.eh.dwarf.cfa(i32 0)
+  call void @_Z1gPv(i8* %0)
+  ret void
+}
+
+declare void @_Z1gPv(i8*)
+
+; Function Attrs: nounwind
+declare i8* @llvm.eh.dwarf.cfa(i32)