llvm/lib/Target/PowerPC/PPCBranchSelector.cpp - toolchain/llvm-project - Gitiles

 //===-- PPCBranchSelector.cpp - Emit long conditional branches ------------===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 //
 // This file contains a pass that scans a machine function to determine which
 // conditional branches need more than 16 bits of displacement to reach their
 // target basic block.  It does this in two passes; a calculation of basic block
 // positions pass, and a branch pseudo op to machine branch opcode pass.  This
 // pass should be run last, just before the assembly printer.
 //
 //===----------------------------------------------------------------------===//

 #include "PPC.h"
 #include "MCTargetDesc/PPCPredicates.h"
 #include "PPCInstrBuilder.h"
 #include "PPCInstrInfo.h"
 #include "PPCSubtarget.h"
 #include "llvm/ADT/Statistic.h"
 #include "llvm/CodeGen/MachineFunctionPass.h"
 #include "llvm/CodeGen/MachineRegisterInfo.h"
 #include "llvm/Support/MathExtras.h"
 #include "llvm/Target/TargetMachine.h"
 #include "llvm/Target/TargetSubtargetInfo.h"
 using namespace llvm;

 #define DEBUG_TYPE "ppc-branch-select"

 STATISTIC(NumExpanded, "Number of branches expanded to long format");

 namespace llvm {
   void initializePPCBSelPass(PassRegistry&);
 }

 namespace {
   struct PPCBSel : public MachineFunctionPass {
     static char ID;
     PPCBSel() : MachineFunctionPass(ID) {
       initializePPCBSelPass(*PassRegistry::getPassRegistry());
     }

     // The sizes of the basic blocks in the function (the first
     // element of the pair); the second element of the pair is the amount of the
     // size that is due to potential padding.
     std::vector<std::pair<unsigned, unsigned>> BlockSizes;

     bool runOnMachineFunction(MachineFunction &Fn) override;

     MachineFunctionProperties getRequiredProperties() const override {
       return MachineFunctionProperties().set(
           MachineFunctionProperties::Property::NoVRegs);
     }

     StringRef getPassName() const override { return "PowerPC Branch Selector"; }
   };
   char PPCBSel::ID = 0;
 }

 INITIALIZE_PASS(PPCBSel, "ppc-branch-select", "PowerPC Branch Selector",
                 false, false)

 /// createPPCBranchSelectionPass - returns an instance of the Branch Selection
 /// Pass
 ///
 FunctionPass *llvm::createPPCBranchSelectionPass() {
   return new PPCBSel();
 }

 bool PPCBSel::runOnMachineFunction(MachineFunction &Fn) {
   const PPCInstrInfo *TII =
       static_cast<const PPCInstrInfo *>(Fn.getSubtarget().getInstrInfo());
   // Give the blocks of the function a dense, in-order, numbering.
   Fn.RenumberBlocks();
   BlockSizes.resize(Fn.getNumBlockIDs());

   auto GetAlignmentAdjustment =
     [](MachineBasicBlock &MBB, unsigned Offset) -> unsigned {
     unsigned Align = MBB.getAlignment();
     if (!Align)
       return 0;

     unsigned AlignAmt = 1 << Align;
     unsigned ParentAlign = MBB.getParent()->getAlignment();

     if (Align <= ParentAlign)
       return OffsetToAlignment(Offset, AlignAmt);

     // The alignment of this MBB is larger than the function's alignment, so we
     // can't tell whether or not it will insert nops. Assume that it will.
     return AlignAmt + OffsetToAlignment(Offset, AlignAmt);
   };

   // We need to be careful about the offset of the first block in the function
   // because it might not have the function's alignment. This happens because,
   // under the ELFv2 ABI, for functions which require a TOC pointer, we add a
   // two-instruction sequence to the start of the function.
   // Note: This needs to be synchronized with the check in
   // PPCLinuxAsmPrinter::EmitFunctionBodyStart.
   unsigned InitialOffset = 0;
   if (Fn.getSubtarget<PPCSubtarget>().isELFv2ABI() &&
       !Fn.getRegInfo().use_empty(PPC::X2))
     InitialOffset = 8;

   // Measure each MBB and compute a size for the entire function.
   unsigned FuncSize = InitialOffset;
   for (MachineFunction::iterator MFI = Fn.begin(), E = Fn.end(); MFI != E;
        ++MFI) {
     MachineBasicBlock *MBB = &*MFI;

     // The end of the previous block may have extra nops if this block has an
     // alignment requirement.
     if (MBB->getNumber() > 0) {
       unsigned AlignExtra = GetAlignmentAdjustment(*MBB, FuncSize);

       auto &BS = BlockSizes[MBB->getNumber()-1];
       BS.first += AlignExtra;
       BS.second = AlignExtra;

       FuncSize += AlignExtra;
     }

     unsigned BlockSize = 0;
     for (MachineInstr &MI : *MBB)
       BlockSize += TII->getInstSizeInBytes(MI);

     BlockSizes[MBB->getNumber()].first = BlockSize;
     FuncSize += BlockSize;
   }

   // If the entire function is smaller than the displacement of a branch field,
   // we know we don't need to shrink any branches in this function.  This is a
   // common case.
   if (FuncSize < (1 << 15)) {
     BlockSizes.clear();
     return false;
   }

   // For each conditional branch, if the offset to its destination is larger
   // than the offset field allows, transform it into a long branch sequence
   // like this:
   //   short branch:
   //     bCC MBB
   //   long branch:
   //     b!CC $PC+8
   //     b MBB
   //
   bool MadeChange = true;
   bool EverMadeChange = false;
   while (MadeChange) {
     // Iteratively expand branches until we reach a fixed point.
     MadeChange = false;

     for (MachineFunction::iterator MFI = Fn.begin(), E = Fn.end(); MFI != E;
          ++MFI) {
       MachineBasicBlock &MBB = *MFI;
       unsigned MBBStartOffset = 0;
       for (MachineBasicBlock::iterator I = MBB.begin(), E = MBB.end();
            I != E; ++I) {
         MachineBasicBlock *Dest = nullptr;
         if (I->getOpcode() == PPC::BCC && !I->getOperand(2).isImm())
           Dest = I->getOperand(2).getMBB();
         else if ((I->getOpcode() == PPC::BC || I->getOpcode() == PPC::BCn) &&
                  !I->getOperand(1).isImm())
           Dest = I->getOperand(1).getMBB();
         else if ((I->getOpcode() == PPC::BDNZ8 || I->getOpcode() == PPC::BDNZ ||
                   I->getOpcode() == PPC::BDZ8  || I->getOpcode() == PPC::BDZ) &&
                  !I->getOperand(0).isImm())
           Dest = I->getOperand(0).getMBB();

         if (!Dest) {
           MBBStartOffset += TII->getInstSizeInBytes(*I);
           continue;
         }

         // Determine the offset from the current branch to the destination
         // block.
         int BranchSize;
         if (Dest->getNumber() <= MBB.getNumber()) {
           // If this is a backwards branch, the delta is the offset from the
           // start of this block to this branch, plus the sizes of all blocks
           // from this block to the dest.
           BranchSize = MBBStartOffset;

           for (unsigned i = Dest->getNumber(), e = MBB.getNumber(); i != e; ++i)
             BranchSize += BlockSizes[i].first;
         } else {
           // Otherwise, add the size of the blocks between this block and the
           // dest to the number of bytes left in this block.
           BranchSize = -MBBStartOffset;

           for (unsigned i = MBB.getNumber(), e = Dest->getNumber(); i != e; ++i)
             BranchSize += BlockSizes[i].first;
         }

         // If this branch is in range, ignore it.
         if (isInt<16>(BranchSize)) {
           MBBStartOffset += 4;
           continue;
         }

         // Otherwise, we have to expand it to a long branch.
         MachineInstr &OldBranch = *I;
         DebugLoc dl = OldBranch.getDebugLoc();

         if (I->getOpcode() == PPC::BCC) {
           // The BCC operands are:
           // 0. PPC branch predicate
           // 1. CR register
           // 2. Target MBB
           PPC::Predicate Pred = (PPC::Predicate)I->getOperand(0).getImm();
           unsigned CRReg = I->getOperand(1).getReg();

           // Jump over the uncond branch inst (i.e. $PC+8) on opposite condition.
           BuildMI(MBB, I, dl, TII->get(PPC::BCC))
             .addImm(PPC::InvertPredicate(Pred)).addReg(CRReg).addImm(2);
         } else if (I->getOpcode() == PPC::BC) {
           unsigned CRBit = I->getOperand(0).getReg();
           BuildMI(MBB, I, dl, TII->get(PPC::BCn)).addReg(CRBit).addImm(2);
         } else if (I->getOpcode() == PPC::BCn) {
           unsigned CRBit = I->getOperand(0).getReg();
           BuildMI(MBB, I, dl, TII->get(PPC::BC)).addReg(CRBit).addImm(2);
         } else if (I->getOpcode() == PPC::BDNZ) {
           BuildMI(MBB, I, dl, TII->get(PPC::BDZ)).addImm(2);
         } else if (I->getOpcode() == PPC::BDNZ8) {
           BuildMI(MBB, I, dl, TII->get(PPC::BDZ8)).addImm(2);
         } else if (I->getOpcode() == PPC::BDZ) {
           BuildMI(MBB, I, dl, TII->get(PPC::BDNZ)).addImm(2);
         } else if (I->getOpcode() == PPC::BDZ8) {
           BuildMI(MBB, I, dl, TII->get(PPC::BDNZ8)).addImm(2);
         } else {
            llvm_unreachable("Unhandled branch type!");
         }

         // Uncond branch to the real destination.
         I = BuildMI(MBB, I, dl, TII->get(PPC::B)).addMBB(Dest);

         // Remove the old branch from the function.
         OldBranch.eraseFromParent();

         // Remember that this instruction is 8-bytes, increase the size of the
         // block by 4, remember to iterate.
         BlockSizes[MBB.getNumber()].first += 4;
         MBBStartOffset += 8;
         ++NumExpanded;
         MadeChange = true;
       }
     }

     if (MadeChange) {
       // If we're going to iterate again, make sure we've updated our
       // padding-based contributions to the block sizes.
       unsigned Offset = InitialOffset;
       for (MachineFunction::iterator MFI = Fn.begin(), E = Fn.end(); MFI != E;
            ++MFI) {
         MachineBasicBlock *MBB = &*MFI;

         if (MBB->getNumber() > 0) {
           auto &BS = BlockSizes[MBB->getNumber()-1];
           BS.first -= BS.second;
           Offset -= BS.second;

           unsigned AlignExtra = GetAlignmentAdjustment(*MBB, Offset);

           BS.first += AlignExtra;
           BS.second = AlignExtra;

           Offset += AlignExtra;
         }

         Offset += BlockSizes[MBB->getNumber()].first;
       }
     }

     EverMadeChange |= MadeChange;
   }

   BlockSizes.clear();
   return true;
 }
	//===-- PPCBranchSelector.cpp - Emit long conditional branches ------------===//
	//
	// The LLVM Compiler Infrastructure
	//
	// This file is distributed under the University of Illinois Open Source
	// License. See LICENSE.TXT for details.
	//
	//===----------------------------------------------------------------------===//
	//
	// This file contains a pass that scans a machine function to determine which
	// conditional branches need more than 16 bits of displacement to reach their
	// target basic block. It does this in two passes; a calculation of basic block
	// positions pass, and a branch pseudo op to machine branch opcode pass. This
	// pass should be run last, just before the assembly printer.
	//
	//===----------------------------------------------------------------------===//

	#include "PPC.h"
	#include "MCTargetDesc/PPCPredicates.h"
	#include "PPCInstrBuilder.h"
	#include "PPCInstrInfo.h"
	#include "PPCSubtarget.h"
	#include "llvm/ADT/Statistic.h"
	#include "llvm/CodeGen/MachineFunctionPass.h"
	#include "llvm/CodeGen/MachineRegisterInfo.h"
	#include "llvm/Support/MathExtras.h"
	#include "llvm/Target/TargetMachine.h"
	#include "llvm/Target/TargetSubtargetInfo.h"
	using namespace llvm;

	#define DEBUG_TYPE "ppc-branch-select"

	STATISTIC(NumExpanded, "Number of branches expanded to long format");

	namespace llvm {
	void initializePPCBSelPass(PassRegistry&);
	}

	namespace {
	struct PPCBSel : public MachineFunctionPass {
	static char ID;
	PPCBSel() : MachineFunctionPass(ID) {
	initializePPCBSelPass(*PassRegistry::getPassRegistry());
	}

	// The sizes of the basic blocks in the function (the first
	// element of the pair); the second element of the pair is the amount of the
	// size that is due to potential padding.
	std::vector<std::pair<unsigned, unsigned>> BlockSizes;

	bool runOnMachineFunction(MachineFunction &Fn) override;

	MachineFunctionProperties getRequiredProperties() const override {
	return MachineFunctionProperties().set(
	MachineFunctionProperties::Property::NoVRegs);
	}

	StringRef getPassName() const override { return "PowerPC Branch Selector"; }
	};
	char PPCBSel::ID = 0;
	}

	INITIALIZE_PASS(PPCBSel, "ppc-branch-select", "PowerPC Branch Selector",
	false, false)

	/// createPPCBranchSelectionPass - returns an instance of the Branch Selection
	/// Pass
	///
	FunctionPass *llvm::createPPCBranchSelectionPass() {
	return new PPCBSel();
	}

	bool PPCBSel::runOnMachineFunction(MachineFunction &Fn) {
	const PPCInstrInfo *TII =
	static_cast<const PPCInstrInfo *>(Fn.getSubtarget().getInstrInfo());
	// Give the blocks of the function a dense, in-order, numbering.
	Fn.RenumberBlocks();
	BlockSizes.resize(Fn.getNumBlockIDs());

	auto GetAlignmentAdjustment =
	[](MachineBasicBlock &MBB, unsigned Offset) -> unsigned {
	unsigned Align = MBB.getAlignment();
	if (!Align)
	return 0;

	unsigned AlignAmt = 1 << Align;
	unsigned ParentAlign = MBB.getParent()->getAlignment();

	if (Align <= ParentAlign)
	return OffsetToAlignment(Offset, AlignAmt);

	// The alignment of this MBB is larger than the function's alignment, so we
	// can't tell whether or not it will insert nops. Assume that it will.
	return AlignAmt + OffsetToAlignment(Offset, AlignAmt);
	};

	// We need to be careful about the offset of the first block in the function
	// because it might not have the function's alignment. This happens because,
	// under the ELFv2 ABI, for functions which require a TOC pointer, we add a
	// two-instruction sequence to the start of the function.
	// Note: This needs to be synchronized with the check in
	// PPCLinuxAsmPrinter::EmitFunctionBodyStart.
	unsigned InitialOffset = 0;
	if (Fn.getSubtarget<PPCSubtarget>().isELFv2ABI() &&
	!Fn.getRegInfo().use_empty(PPC::X2))
	InitialOffset = 8;

	// Measure each MBB and compute a size for the entire function.
	unsigned FuncSize = InitialOffset;
	for (MachineFunction::iterator MFI = Fn.begin(), E = Fn.end(); MFI != E;
	++MFI) {
	MachineBasicBlock MBB = &MFI;

	// The end of the previous block may have extra nops if this block has an
	// alignment requirement.
	if (MBB->getNumber() > 0) {
	unsigned AlignExtra = GetAlignmentAdjustment(*MBB, FuncSize);

	auto &BS = BlockSizes[MBB->getNumber()-1];
	BS.first += AlignExtra;
	BS.second = AlignExtra;

	FuncSize += AlignExtra;
	}

	unsigned BlockSize = 0;
	for (MachineInstr &MI : *MBB)
	BlockSize += TII->getInstSizeInBytes(MI);

	BlockSizes[MBB->getNumber()].first = BlockSize;
	FuncSize += BlockSize;
	}

	// If the entire function is smaller than the displacement of a branch field,
	// we know we don't need to shrink any branches in this function. This is a
	// common case.
	if (FuncSize < (1 << 15)) {
	BlockSizes.clear();
	return false;
	}

	// For each conditional branch, if the offset to its destination is larger
	// than the offset field allows, transform it into a long branch sequence
	// like this:
	// short branch:
	// bCC MBB
	// long branch:
	// b!CC $PC+8
	// b MBB
	//
	bool MadeChange = true;
	bool EverMadeChange = false;
	while (MadeChange) {
	// Iteratively expand branches until we reach a fixed point.
	MadeChange = false;

	for (MachineFunction::iterator MFI = Fn.begin(), E = Fn.end(); MFI != E;
	++MFI) {
	MachineBasicBlock &MBB = *MFI;
	unsigned MBBStartOffset = 0;
	for (MachineBasicBlock::iterator I = MBB.begin(), E = MBB.end();
	I != E; ++I) {
	MachineBasicBlock *Dest = nullptr;
	if (I->getOpcode() == PPC::BCC && !I->getOperand(2).isImm())
	Dest = I->getOperand(2).getMBB();
	else if ((I->getOpcode() == PPC::BC \|\| I->getOpcode() == PPC::BCn) &&
	!I->getOperand(1).isImm())
	Dest = I->getOperand(1).getMBB();
	else if ((I->getOpcode() == PPC::BDNZ8 \|\| I->getOpcode() == PPC::BDNZ \|\|
	I->getOpcode() == PPC::BDZ8 \|\| I->getOpcode() == PPC::BDZ) &&
	!I->getOperand(0).isImm())
	Dest = I->getOperand(0).getMBB();

	if (!Dest) {
	MBBStartOffset += TII->getInstSizeInBytes(*I);
	continue;
	}

	// Determine the offset from the current branch to the destination
	// block.
	int BranchSize;
	if (Dest->getNumber() <= MBB.getNumber()) {
	// If this is a backwards branch, the delta is the offset from the
	// start of this block to this branch, plus the sizes of all blocks
	// from this block to the dest.
	BranchSize = MBBStartOffset;

	for (unsigned i = Dest->getNumber(), e = MBB.getNumber(); i != e; ++i)
	BranchSize += BlockSizes[i].first;
	} else {
	// Otherwise, add the size of the blocks between this block and the
	// dest to the number of bytes left in this block.
	BranchSize = -MBBStartOffset;

	for (unsigned i = MBB.getNumber(), e = Dest->getNumber(); i != e; ++i)
	BranchSize += BlockSizes[i].first;
	}

	// If this branch is in range, ignore it.
	if (isInt<16>(BranchSize)) {
	MBBStartOffset += 4;
	continue;
	}

	// Otherwise, we have to expand it to a long branch.
	MachineInstr &OldBranch = *I;
	DebugLoc dl = OldBranch.getDebugLoc();

	if (I->getOpcode() == PPC::BCC) {
	// The BCC operands are:
	// 0. PPC branch predicate
	// 1. CR register
	// 2. Target MBB
	PPC::Predicate Pred = (PPC::Predicate)I->getOperand(0).getImm();
	unsigned CRReg = I->getOperand(1).getReg();

	// Jump over the uncond branch inst (i.e. $PC+8) on opposite condition.
	BuildMI(MBB, I, dl, TII->get(PPC::BCC))
	.addImm(PPC::InvertPredicate(Pred)).addReg(CRReg).addImm(2);
	} else if (I->getOpcode() == PPC::BC) {
	unsigned CRBit = I->getOperand(0).getReg();
	BuildMI(MBB, I, dl, TII->get(PPC::BCn)).addReg(CRBit).addImm(2);
	} else if (I->getOpcode() == PPC::BCn) {
	unsigned CRBit = I->getOperand(0).getReg();
	BuildMI(MBB, I, dl, TII->get(PPC::BC)).addReg(CRBit).addImm(2);
	} else if (I->getOpcode() == PPC::BDNZ) {
	BuildMI(MBB, I, dl, TII->get(PPC::BDZ)).addImm(2);
	} else if (I->getOpcode() == PPC::BDNZ8) {
	BuildMI(MBB, I, dl, TII->get(PPC::BDZ8)).addImm(2);
	} else if (I->getOpcode() == PPC::BDZ) {
	BuildMI(MBB, I, dl, TII->get(PPC::BDNZ)).addImm(2);
	} else if (I->getOpcode() == PPC::BDZ8) {
	BuildMI(MBB, I, dl, TII->get(PPC::BDNZ8)).addImm(2);
	} else {
	llvm_unreachable("Unhandled branch type!");
	}

	// Uncond branch to the real destination.
	I = BuildMI(MBB, I, dl, TII->get(PPC::B)).addMBB(Dest);

	// Remove the old branch from the function.
	OldBranch.eraseFromParent();

	// Remember that this instruction is 8-bytes, increase the size of the
	// block by 4, remember to iterate.
	BlockSizes[MBB.getNumber()].first += 4;
	MBBStartOffset += 8;
	++NumExpanded;
	MadeChange = true;
	}
	}

	if (MadeChange) {
	// If we're going to iterate again, make sure we've updated our
	// padding-based contributions to the block sizes.
	unsigned Offset = InitialOffset;
	for (MachineFunction::iterator MFI = Fn.begin(), E = Fn.end(); MFI != E;
	++MFI) {
	MachineBasicBlock MBB = &MFI;

	if (MBB->getNumber() > 0) {
	auto &BS = BlockSizes[MBB->getNumber()-1];
	BS.first -= BS.second;
	Offset -= BS.second;

	unsigned AlignExtra = GetAlignmentAdjustment(*MBB, Offset);

	BS.first += AlignExtra;
	BS.second = AlignExtra;

	Offset += AlignExtra;
	}

	Offset += BlockSizes[MBB->getNumber()].first;
	}
	}

	EverMadeChange \|= MadeChange;
	}

	BlockSizes.clear();
	return true;
	}