diff options
Diffstat (limited to 'llvm/lib/Target/PowerPC')
| -rw-r--r-- | llvm/lib/Target/PowerPC/PPCFrameLowering.cpp | 66 | ||||
| -rw-r--r-- | llvm/lib/Target/PowerPC/PPCFrameLowering.h | 29 |
2 files changed, 91 insertions, 4 deletions
diff --git a/llvm/lib/Target/PowerPC/PPCFrameLowering.cpp b/llvm/lib/Target/PowerPC/PPCFrameLowering.cpp index 6d90710599e..c7a3bbd3762 100644 --- a/llvm/lib/Target/PowerPC/PPCFrameLowering.cpp +++ b/llvm/lib/Target/PowerPC/PPCFrameLowering.cpp @@ -556,6 +556,58 @@ void PPCFrameLowering::replaceFPWithRealFP(MachineFunction &MF) const { } } +bool PPCFrameLowering::findScratchRegister(MachineBasicBlock *MBB, + bool UseAtEnd, + unsigned *ScratchRegister) const { + RegScavenger RS; + unsigned R0 = Subtarget.isPPC64() ? PPC::X0 : PPC::R0; + + if (ScratchRegister) + *ScratchRegister = R0; + + // If MBB is an entry or exit block, use R0 as the scratch register + if ((UseAtEnd && MBB->isReturnBlock()) || + (!UseAtEnd && (&MBB->getParent()->front() == MBB))) + return true; + + RS.initRegState(); + RS.enterBasicBlock(MBB); + + // The scratch register will be used at the end of the block, so must consider + // all registers used within the block + if (UseAtEnd && MBB->begin() != MBB->getFirstTerminator()) + RS.forward(MBB->getFirstTerminator()); + + if (!RS.isRegUsed(R0)) + return true; + + unsigned Reg = RS.FindUnusedReg(Subtarget.isPPC64() ? &PPC::G8RCRegClass + : &PPC::GPRCRegClass); + + // Make sure the register scavenger was able to find an available register + // If not, use R0 but return false to indicate no register was available and + // R0 must be used (as recommended by the ABI) + if (Reg == 0) + return false; + + if (ScratchRegister) + *ScratchRegister = Reg; + + return true; +} + +bool PPCFrameLowering::canUseAsPrologue(const MachineBasicBlock &MBB) const { + MachineBasicBlock *TmpMBB = const_cast<MachineBasicBlock *>(&MBB); + + return findScratchRegister(TmpMBB, false, nullptr); +} + +bool PPCFrameLowering::canUseAsEpilogue(const MachineBasicBlock &MBB) const { + MachineBasicBlock *TmpMBB = const_cast<MachineBasicBlock *>(&MBB); + + return findScratchRegister(TmpMBB, true, nullptr); +} + void PPCFrameLowering::emitPrologue(MachineFunction &MF, MachineBasicBlock &MBB) const { MachineBasicBlock::iterator MBBI = MBB.begin(); @@ -613,7 +665,7 @@ void PPCFrameLowering::emitPrologue(MachineFunction &MF, unsigned BPReg = RegInfo->getBaseRegister(MF); unsigned FPReg = isPPC64 ? PPC::X31 : PPC::R31; unsigned LRReg = isPPC64 ? PPC::LR8 : PPC::LR; - unsigned ScratchReg = isPPC64 ? PPC::X0 : PPC::R0; + unsigned ScratchReg = 0; unsigned TempReg = isPPC64 ? PPC::X12 : PPC::R12; // another scratch reg // ...(R12/X12 is volatile in both Darwin & SVR4, & can't be a function arg.) const MCInstrDesc& MFLRInst = TII.get(isPPC64 ? PPC::MFLR8 @@ -642,6 +694,9 @@ void PPCFrameLowering::emitPrologue(MachineFunction &MF, assert((isPPC64 || !isSVR4ABI || !(!FrameSize && (MustSaveLR || HasFP))) && "FrameSize must be >0 to save/restore the FP or LR for 32-bit SVR4."); + findScratchRegister(&MBB, false, &ScratchReg); + assert(ScratchReg && "No scratch register!"); + int LROffset = getReturnSaveOffset(); int FPOffset = 0; @@ -950,7 +1005,7 @@ void PPCFrameLowering::emitEpilogue(MachineFunction &MF, unsigned SPReg = isPPC64 ? PPC::X1 : PPC::R1; unsigned BPReg = RegInfo->getBaseRegister(MF); unsigned FPReg = isPPC64 ? PPC::X31 : PPC::R31; - unsigned ScratchReg = isPPC64 ? PPC::X0 : PPC::R0; + unsigned ScratchReg = 0; unsigned TempReg = isPPC64 ? PPC::X12 : PPC::R12; // another scratch reg const MCInstrDesc& MTLRInst = TII.get( isPPC64 ? PPC::MTLR8 : PPC::MTLR ); @@ -964,10 +1019,14 @@ void PPCFrameLowering::emitEpilogue(MachineFunction &MF, : PPC::ADDI ); const MCInstrDesc& AddInst = TII.get( isPPC64 ? PPC::ADD8 : PPC::ADD4 ); - + int LROffset = getReturnSaveOffset(); int FPOffset = 0; + + findScratchRegister(&MBB, true, &ScratchReg); + assert(ScratchReg && "No scratch register!"); + if (HasFP) { if (isSVR4ABI) { MachineFrameInfo *FFI = MF.getFrameInfo(); @@ -1062,7 +1121,6 @@ void PPCFrameLowering::emitEpilogue(MachineFunction &MF, .addImm(0) .addReg(SPReg); } - } if (MustSaveLR) diff --git a/llvm/lib/Target/PowerPC/PPCFrameLowering.h b/llvm/lib/Target/PowerPC/PPCFrameLowering.h index 3130a55a33a..bbe1329a535 100644 --- a/llvm/lib/Target/PowerPC/PPCFrameLowering.h +++ b/llvm/lib/Target/PowerPC/PPCFrameLowering.h @@ -29,6 +29,30 @@ class PPCFrameLowering: public TargetFrameLowering { const unsigned LinkageSize; const unsigned BasePointerSaveOffset; + /** + * \brief Find a register that can be used in function prologue and epilogue + * + * Find a register that can be use as the scratch register in function + * prologue and epilogue to save various registers (Link Register, Base + * Pointer, etc.). Prefer R0, if it is available. If it is not available, + * then choose a different register. + * + * This method will return true if an available register was found (including + * R0). If no available registers are found, the method returns false and sets + * ScratchRegister to R0, as per the recommendation in the ABI. + * + * \param[in] MBB The machine basic block to find an available register for + * \param[in] UseAtEnd Specify whether the scratch register will be used at + * the end of the basic block (i.e., will the scratch + * register kill a register defined in the basic block) + * \param[out] ScratchRegister The scratch register to use + * \return true if a scratch register was found. false of a scratch register + * was not found and R0 is being used as the default. + */ + bool findScratchRegister(MachineBasicBlock *MBB, + bool UseAtEnd, + unsigned *ScratchRegister) const; + public: PPCFrameLowering(const PPCSubtarget &STI); @@ -94,6 +118,11 @@ public: getCalleeSavedSpillSlots(unsigned &NumEntries) const override; bool enableShrinkWrapping(const MachineFunction &MF) const override; + + /// Methods used by shrink wrapping to determine if MBB can be used for the + /// function prologue/epilogue. + bool canUseAsPrologue(const MachineBasicBlock &MBB) const override; + bool canUseAsEpilogue(const MachineBasicBlock &MBB) const override; }; } // End llvm namespace |
