[llvm] [AArch64] Use helper class for emitting CFI instructions into MIR (NFCI) (PR #136004)

[Daniel Hoekwater via llvm-commits]

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@@ -602,33 +603,23 @@ void AArch64FrameLowering::emitCalleeSavedGPRLocations(
   if (CSI.empty())
     return;
 
-  const TargetSubtargetInfo &STI = MF.getSubtarget();
-  const TargetRegisterInfo &TRI = *STI.getRegisterInfo();
-  const TargetInstrInfo &TII = *STI.getInstrInfo();
-  DebugLoc DL = MBB.findDebugLoc(MBBI);
-
+  CFIInstBuilder CFIBuilder(MBB, MBBI, MachineInstr::FrameSetup);
   for (const auto &Info : CSI) {
     unsigned FrameIdx = Info.getFrameIdx();
     if (MFI.getStackID(FrameIdx) == TargetStackID::ScalableVector)
       continue;
 
     assert(!Info.isSpilledToReg() && "Spilling to registers not implemented");
-    int64_t DwarfReg = TRI.getDwarfRegNum(Info.getReg(), true);
     int64_t Offset = MFI.getObjectOffset(FrameIdx) - getOffsetOfLocalArea();
 
     // The location of VG will be emitted before each streaming-mode change in
     // the function. Only locally-streaming functions require emitting the
     // non-streaming VG location here.
     if ((LocallyStreaming && FrameIdx == AFI->getStreamingVGIdx()) ||
-        (!LocallyStreaming &&
-         DwarfReg == TRI.getDwarfRegNum(AArch64::VG, true)))
+        (!LocallyStreaming && Info.getReg() == AArch64::VG))
       continue;
 
-    unsigned CFIIndex = MF.addFrameInst(
-        MCCFIInstruction::createOffset(nullptr, DwarfReg, Offset));
-    BuildMI(MBB, MBBI, DL, TII.get(TargetOpcode::CFI_INSTRUCTION))
-        .addCFIIndex(CFIIndex)
-        .setMIFlags(MachineInstr::FrameSetup);
+    CFIBuilder.buildOffset(Info.getReg(), Offset);
----------------
dhoekwater wrote:

(Here and elsewhere) if `CFIInstBuilder` isn't too expensive to construct, it may be more readable to declare `CFIBuilder` closer to its use so it's clear you're building a `MachineInstr::FrameSetup` instruction.

Alternatively, you could get rid of the local variable entirely and do `CFIInstBuilder(MBB, MBBI, MachineInstr::FrameSetup).buildOffset(Info.getReg(), Offset)` instead.

https://github.com/llvm/llvm-project/pull/136004