[PATCH] D126181: [RISCV] Add ISD::EH_DWARF_CFA

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Based on D24038 <https://reviews.llvm.org/D24038>.
LLVM has an @llvm.eh.dwarf.cfa intrinsic, used to lower the GCC-compatible __builtin_dwarf_cfa() builtin.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D126181

Files:
  llvm/lib/Target/RISCV/RISCVISelLowering.cpp
  llvm/lib/Target/RISCV/RISCVISelLowering.h
  llvm/test/CodeGen/RISCV/eh-dwarf-cfa.ll


Index: llvm/test/CodeGen/RISCV/eh-dwarf-cfa.ll
===================================================================
--- /dev/null
+++ llvm/test/CodeGen/RISCV/eh-dwarf-cfa.ll
@@ -0,0 +1,38 @@
+; 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 at 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 at 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)
Index: llvm/lib/Target/RISCV/RISCVISelLowering.h
===================================================================
--- llvm/lib/Target/RISCV/RISCVISelLowering.h
+++ llvm/lib/Target/RISCV/RISCVISelLowering.h
@@ -664,6 +664,8 @@
   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;
 
Index: llvm/lib/Target/RISCV/RISCVISelLowering.cpp
===================================================================
--- llvm/lib/Target/RISCV/RISCVISelLowering.cpp
+++ llvm/lib/Target/RISCV/RISCVISelLowering.cpp
@@ -187,6 +187,10 @@
   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);
 
@@ -3422,6 +3426,8 @@
     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:
@@ -6606,6 +6612,16 @@
                      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:


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