[ARM][NFC] Tidy up subtarget frame pointer routines

[tmatheson]

Summary

getFramePointerReg only depends on information in ARMSubtarget,
so move it in there so it can be accessed from more places.

Make use of ARMSubtarget::getFramePointerReg to remove duplicated code.

The main use of useR7AsFramePointer is getFramePointerReg, so inline it.

[tmatheson]

clang-format (ignoring indentation change ARMAsmPrinter.cpp in match rest of file)

[tmatheson]

clang-format everything for CI

[DavidSpickett]

LGTM

llvm/lib/Target/ARM/ARMSubtarget.h

826

And fix this warning.

[tmatheson]

Fix clang-tidy: warning: do not use 'else' after 'return'

[pratlucas]

LGTM.

llvm/lib/Target/ARM/ARMAsmPrinter.cpp

 //===-- ARMAsmPrinter.cpp - Print machine code to an ARM .s file ----------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 //
 // This file contains a printer that converts from our internal representation

 
 void ARMAsmPrinter::emitInstruction(const MachineInstr *MI) {
   const DataLayout &DL = getDataLayout();
   MCTargetStreamer &TS = *OutStreamer->getTargetStreamer();
   ARMTargetStreamer &ATS = static_cast<ARMTargetStreamer &>(TS);
 
   const MachineFunction &MF = *MI->getParent()->getParent();
   const ARMSubtarget &STI = MF.getSubtarget<ARMSubtarget>();
-  unsigned FramePtr = STI.useR7AsFramePointer() ? ARM::R7 : ARM::R11;
 
   // If we just ended a constant pool, mark it as such.
   if (InConstantPool && MI->getOpcode() != ARM::CONSTPOOL_ENTRY) {
     OutStreamer->emitDataRegion(MCDR_DataRegionEnd);
     InConstantPool = false;
   }
 
   // Emit unwinding stuff for frame-related instructions
EmitToStreamer(*OutStreamer, MCInstBuilder(ARM::LDRi12)
       .addImm(4)
       // Predicate.
       .addImm(ARMCC::AL)
       .addReg(0));
 
     if (STI.isTargetDarwin() || STI.isTargetWindows()) {
       // These platforms always use the same frame register
       EmitToStreamer(*OutStreamer, MCInstBuilder(ARM::LDRi12)
-        .addReg(FramePtr)
+        .addReg(STI.getFramePointerReg())
         .addReg(SrcReg)
         .addImm(0)
         // Predicate.
         .addImm(ARMCC::AL)
         .addReg(0));
     } else {
       // If the calling code might use either R7 or R11 as
       // frame pointer register, restore it into both.
EmitToStreamer(*OutStreamer, MCInstBuilder(ARM::tLDRi)
       .addImm(1)
       // Predicate.
       .addImm(ARMCC::AL)
       .addReg(0));
 
     if (STI.isTargetDarwin() || STI.isTargetWindows()) {
       // These platforms always use the same frame register
       EmitToStreamer(*OutStreamer, MCInstBuilder(ARM::tLDRi)
-        .addReg(FramePtr)
+        .addReg(STI.getFramePointerReg())
         .addReg(SrcReg)
         .addImm(0)
         // Predicate.
         .addImm(ARMCC::AL)
         .addReg(0));
     } else {
       // If the calling code might use either R7 or R11 as
       // frame pointer register, restore it into both.

llvm/lib/Target/ARM/ARMBaseRegisterInfo.cpp

 
 using namespace llvm;
 
 ARMBaseRegisterInfo::ARMBaseRegisterInfo()
     : ARMGenRegisterInfo(ARM::LR, 0, 0, ARM::PC) {
   ARM_MC::initLLVMToCVRegMapping(this);
 }
 
-static unsigned getFramePointerReg(const ARMSubtarget &STI) {
-  return STI.useR7AsFramePointer() ? ARM::R7 : ARM::R11;
-}
-
 const MCPhysReg*
 ARMBaseRegisterInfo::getCalleeSavedRegs(const MachineFunction *MF) const {
   const ARMSubtarget &STI = MF->getSubtarget<ARMSubtarget>();
   bool UseSplitPush = STI.splitFramePushPop(*MF);
   const MCPhysReg *RegList =
       STI.isTargetDarwin()
           ? CSR_iOS_SaveList
           : (UseSplitPush ? CSR_AAPCS_SplitPush_SaveList : CSR_AAPCS_SaveList);
getReservedRegs(const MachineFunction &MF) const {
 
   // FIXME: avoid re-calculating this every time.
   BitVector Reserved(getNumRegs());
   markSuperRegs(Reserved, ARM::SP);
   markSuperRegs(Reserved, ARM::PC);
   markSuperRegs(Reserved, ARM::FPSCR);
   markSuperRegs(Reserved, ARM::APSR_NZCV);
   if (TFI->hasFP(MF))
-    markSuperRegs(Reserved, getFramePointerReg(STI));
+    markSuperRegs(Reserved, STI.getFramePointerReg());
   if (hasBasePointer(MF))
     markSuperRegs(Reserved, BasePtr);
   // Some targets reserve R9.
   if (STI.isR9Reserved())
     markSuperRegs(Reserved, ARM::R9);
   // Reserve D16-D31 if the subtarget doesn't support them.
   if (!STI.hasD32()) {
     static_assert(ARM::D31 == ARM::D16 + 15, "Register list not consecutive!");

 bool ARMBaseRegisterInfo::isInlineAsmReadOnlyReg(const MachineFunction &MF,
                                                  unsigned PhysReg) const {
   const ARMSubtarget &STI = MF.getSubtarget<ARMSubtarget>();
   const ARMFrameLowering *TFI = getFrameLowering(MF);
 
   BitVector Reserved(getNumRegs());
   markSuperRegs(Reserved, ARM::PC);
   if (TFI->hasFP(MF))
-    markSuperRegs(Reserved, getFramePointerReg(STI));
+    markSuperRegs(Reserved, STI.getFramePointerReg());
   if (hasBasePointer(MF))
     markSuperRegs(Reserved, BasePtr);
   assert(checkAllSuperRegsMarked(Reserved));
   return Reserved.test(PhysReg);
 }
 
 const TargetRegisterClass *
 ARMBaseRegisterInfo::getLargestLegalSuperClass(const TargetRegisterClass *RC,
bool ARMBaseRegisterInfo::hasBasePointer(const MachineFunction &MF) const {
   if (AFI->isThumb1OnlyFunction() && !TFI->hasReservedCallFrame(MF))
     return true;
   return false;
 }
 
 bool ARMBaseRegisterInfo::canRealignStack(const MachineFunction &MF) const {
   const MachineRegisterInfo *MRI = &MF.getRegInfo();
   const ARMFrameLowering *TFI = getFrameLowering(MF);
+  const ARMSubtarget &STI = MF.getSubtarget<ARMSubtarget>();
   // We can't realign the stack if:
   // 1. Dynamic stack realignment is explicitly disabled,
   // 2. There are VLAs in the function and the base pointer is disabled.
   if (!TargetRegisterInfo::canRealignStack(MF))
     return false;
   // Stack realignment requires a frame pointer.  If we already started
   // register allocation with frame pointer elimination, it is too late now.
-  if (!MRI->canReserveReg(getFramePointerReg(MF.getSubtarget<ARMSubtarget>())))
+  if (!MRI->canReserveReg(STI.getFramePointerReg()))
     return false;
   // We may also need a base pointer if there are dynamic allocas or stack
   // pointer adjustments around calls.
   if (TFI->hasReservedCallFrame(MF))
     return true;
   // A base pointer is required and allowed.  Check that it isn't too late to
   // reserve it.
   return MRI->canReserveReg(BasePtr);

 }
 
 Register
 ARMBaseRegisterInfo::getFrameRegister(const MachineFunction &MF) const {
   const ARMSubtarget &STI = MF.getSubtarget<ARMSubtarget>();
   const ARMFrameLowering *TFI = getFrameLowering(MF);
 
   if (TFI->hasFP(MF))
-    return getFramePointerReg(STI);
+    return STI.getFramePointerReg();
   return ARM::SP;
 }
 
 /// emitLoadConstPool - Emits a load from constpool to materialize the
 /// specified immediate.
 void ARMBaseRegisterInfo::emitLoadConstPool(
     MachineBasicBlock &MBB, MachineBasicBlock::iterator &MBBI,
     const DebugLoc &dl, Register DestReg, unsigned SubIdx, int Val,
bool ARMBaseRegisterInfo::shouldRewriteCopySrc(const TargetRegisterClass *DefRC,
   if (DefRC == &ARM::SPRRegClass && DefSubReg == 0 &&
       SrcRC == &ARM::DPRRegClass &&
       (SrcSubReg == ARM::ssub_0 || SrcSubReg == ARM::ssub_1))
     return false;
 
   return TargetRegisterInfo::shouldRewriteCopySrc(DefRC, DefSubReg,
                                                   SrcRC, SrcSubReg);
 }
 No newline at end of file

llvm/lib/Target/ARM/ARMFrameLowering.cpp

 //   more-than-default alignment requirements.
 //
 // In some cases when a base pointer is not strictly needed, it is generated
 // anyway when offsets from the frame pointer to access local variables become
 // so large that the offset can't be encoded in the immediate fields of loads
 // or stores.
 //
 // The frame pointer might be chosen to be r7 or r11, depending on the target
-// architecture and operating system. See ARMSubtarget::useR7AsFramePointer for
+// architecture and operating system. See ARMSubtarget::getFramePointerReg for
 // details.
 //
 // Outgoing function arguments must be at the bottom of the stack frame when
 // calling another function. If we do not have variable-sized stack objects, we
 // can allocate a "reserved call frame" area at the bottom of the local
 // variable area, large enough for all outgoing calls. If we do have VLAs, then
 // the stack pointer must be decremented and incremented around each call to
 // make space for the arguments below the VLAs.

llvm/lib/Target/ARM/ARMSubtarget.h

public:
   bool isRClass() const { return ARMProcClass == RClass; }
   bool isAClass() const { return ARMProcClass == AClass; }
   bool isReadTPHard() const { return ReadTPHard; }
 
   bool isR9Reserved() const {
     return isTargetMachO() ? (ReserveR9 || !HasV6Ops) : ReserveR9;
   }
 
-  bool useR7AsFramePointer() const {
-    return isTargetDarwin() || (!isTargetWindows() && isThumb());
+  MCPhysReg getFramePointerReg() const {
+    if (isTargetDarwin() || (!isTargetWindows() && isThumb()))
+      return ARM::R7;
+    else
+      return ARM::R11;
   }
 
   /// Returns true if the frame setup is split into two separate pushes (first
   /// r0-r7,lr then r8-r11), principally so that the frame pointer is adjacent
   /// to lr. This is always required on Thumb1-only targets, as the push and
   /// pop instructions can't access the high registers.
   bool splitFramePushPop(const MachineFunction &MF) const {
-    return (useR7AsFramePointer() &&
+    return (getFramePointerReg() == ARM::R7 &&
             MF.getTarget().Options.DisableFramePointerElim(MF)) ||
            isThumb1Only();
   }
 
   bool useStride4VFPs() const;
 
   bool useMovt() const;
 

llvm/lib/Target/ARM/Thumb1FrameLowering.cpp

bool Thumb1FrameLowering::emitPopSpecialFixUp(MachineBasicBlock &MBB,
   unsigned PopReg = 0;
   // And some temporary register, just in case.
   unsigned TemporaryReg = 0;
   BitVector PopFriendly =
       TRI.getAllocatableSet(MF, TRI.getRegClass(ARM::tGPRRegClassID));
   // R7 may be used as a frame pointer, hence marked as not generally
   // allocatable, however there's no reason to not use it as a temporary for
   // restoring LR.
-  if (STI.useR7AsFramePointer())
+  if (STI.getFramePointerReg() == ARM::R7)
     PopFriendly.set(ARM::R7);
 
   assert(PopFriendly.any() && "No allocatable pop-friendly register?!");
   // Rebuild the GPRs from the high registers because they are removed
   // form the GPR reg class for thumb1.
   BitVector GPRsNoLRSP =
       TRI.getAllocatableSet(MF, TRI.getRegClass(ARM::hGPRRegClassID));
   GPRsNoLRSP |= PopFriendly;