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diff --git a/llvm/lib/Target/PowerPC/PPCBranchSelector.cpp b/llvm/lib/Target/PowerPC/PPCBranchSelector.cpp
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+//===-- PPCBranchSelector.cpp - Emit long conditional branches ------------===//
+//
+// 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 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 "MCTargetDesc/PPCPredicates.h"
+#include "PPC.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/CodeGen/TargetSubtargetInfo.h"
+#include "llvm/Support/MathExtras.h"
+#include "llvm/Target/TargetMachine.h"
+#include <algorithm>
+using namespace llvm;
+
+#define DEBUG_TYPE "ppc-branch-select"
+
+STATISTIC(NumExpanded, "Number of branches expanded to long format");
+
+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;
+
+ // The first block number which has imprecise instruction address.
+ int FirstImpreciseBlock = -1;
+
+ unsigned GetAlignmentAdjustment(MachineBasicBlock &MBB, unsigned Offset);
+ unsigned ComputeBlockSizes(MachineFunction &Fn);
+ void modifyAdjustment(MachineFunction &Fn);
+ int computeBranchSize(MachineFunction &Fn,
+ const MachineBasicBlock *Src,
+ const MachineBasicBlock *Dest,
+ unsigned BrOffset);
+
+ 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();
+}
+
+/// In order to make MBB aligned, we need to add an adjustment value to the
+/// original Offset.
+unsigned PPCBSel::GetAlignmentAdjustment(MachineBasicBlock &MBB,
+ unsigned Offset) {
+ const Align Alignment = MBB.getAlignment();
+ if (Alignment == Align::None())
+ return 0;
+
+ const Align ParentAlign = MBB.getParent()->getAlignment();
+
+ if (Alignment <= ParentAlign)
+ return offsetToAlignment(Offset, Alignment);
+
+ // 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.
+ if (FirstImpreciseBlock < 0)
+ FirstImpreciseBlock = MBB.getNumber();
+ return Alignment.value() + offsetToAlignment(Offset, Alignment);
+}
+
+/// 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.
+static inline unsigned GetInitialOffset(MachineFunction &Fn) {
+ unsigned InitialOffset = 0;
+ if (Fn.getSubtarget<PPCSubtarget>().isELFv2ABI() &&
+ !Fn.getRegInfo().use_empty(PPC::X2))
+ InitialOffset = 8;
+ return InitialOffset;
+}
+
+/// Measure each MBB and compute a size for the entire function.
+unsigned PPCBSel::ComputeBlockSizes(MachineFunction &Fn) {
+ const PPCInstrInfo *TII =
+ static_cast<const PPCInstrInfo *>(Fn.getSubtarget().getInstrInfo());
+ unsigned FuncSize = GetInitialOffset(Fn);
+
+ 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);
+ if (MI.isInlineAsm() && (FirstImpreciseBlock < 0))
+ FirstImpreciseBlock = MBB->getNumber();
+ }
+
+ BlockSizes[MBB->getNumber()].first = BlockSize;
+ FuncSize += BlockSize;
+ }
+
+ return FuncSize;
+}
+
+/// Modify the basic block align adjustment.
+void PPCBSel::modifyAdjustment(MachineFunction &Fn) {
+ unsigned Offset = GetInitialOffset(Fn);
+ 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;
+ }
+}
+
+/// Determine the offset from the branch in Src block to the Dest block.
+/// BrOffset is the offset of the branch instruction inside Src block.
+int PPCBSel::computeBranchSize(MachineFunction &Fn,
+ const MachineBasicBlock *Src,
+ const MachineBasicBlock *Dest,
+ unsigned BrOffset) {
+ int BranchSize;
+ Align MaxAlign = Align(4);
+ bool NeedExtraAdjustment = false;
+ if (Dest->getNumber() <= Src->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 = BrOffset;
+ MaxAlign = std::max(MaxAlign, Src->getAlignment());
+
+ int DestBlock = Dest->getNumber();
+ BranchSize += BlockSizes[DestBlock].first;
+ for (unsigned i = DestBlock+1, e = Src->getNumber(); i < e; ++i) {
+ BranchSize += BlockSizes[i].first;
+ MaxAlign = std::max(MaxAlign, Fn.getBlockNumbered(i)->getAlignment());
+ }
+
+ NeedExtraAdjustment = (FirstImpreciseBlock >= 0) &&
+ (DestBlock >= FirstImpreciseBlock);
+ } else {
+ // Otherwise, add the size of the blocks between this block and the
+ // dest to the number of bytes left in this block.
+ unsigned StartBlock = Src->getNumber();
+ BranchSize = BlockSizes[StartBlock].first - BrOffset;
+
+ MaxAlign = std::max(MaxAlign, Dest->getAlignment());
+ for (unsigned i = StartBlock+1, e = Dest->getNumber(); i != e; ++i) {
+ BranchSize += BlockSizes[i].first;
+ MaxAlign = std::max(MaxAlign, Fn.getBlockNumbered(i)->getAlignment());
+ }
+
+ NeedExtraAdjustment = (FirstImpreciseBlock >= 0) &&
+ (Src->getNumber() >= FirstImpreciseBlock);
+ }
+
+ // We tend to over estimate code size due to large alignment and
+ // inline assembly. Usually it causes larger computed branch offset.
+ // But sometimes it may also causes smaller computed branch offset
+ // than actual branch offset. If the offset is close to the limit of
+ // encoding, it may cause problem at run time.
+ // Following is a simplified example.
+ //
+ // actual estimated
+ // address address
+ // ...
+ // bne Far 100 10c
+ // .p2align 4
+ // Near: 110 110
+ // ...
+ // Far: 8108 8108
+ //
+ // Actual offset: 0x8108 - 0x100 = 0x8008
+ // Computed offset: 0x8108 - 0x10c = 0x7ffc
+ //
+ // This example also shows when we can get the largest gap between
+ // estimated offset and actual offset. If there is an aligned block
+ // ABB between branch and target, assume its alignment is <align>
+ // bits. Now consider the accumulated function size FSIZE till the end
+ // of previous block PBB. If the estimated FSIZE is multiple of
+ // 2^<align>, we don't need any padding for the estimated address of
+ // ABB. If actual FSIZE at the end of PBB is 4 bytes more than
+ // multiple of 2^<align>, then we need (2^<align> - 4) bytes of
+ // padding. It also means the actual branch offset is (2^<align> - 4)
+ // larger than computed offset. Other actual FSIZE needs less padding
+ // bytes, so causes smaller gap between actual and computed offset.
+ //
+ // On the other hand, if the inline asm or large alignment occurs
+ // between the branch block and destination block, the estimated address
+ // can be <delta> larger than actual address. If padding bytes are
+ // needed for a later aligned block, the actual number of padding bytes
+ // is at most <delta> more than estimated padding bytes. So the actual
+ // aligned block address is less than or equal to the estimated aligned
+ // block address. So the actual branch offset is less than or equal to
+ // computed branch offset.
+ //
+ // The computed offset is at most ((1 << alignment) - 4) bytes smaller
+ // than actual offset. So we add this number to the offset for safety.
+ if (NeedExtraAdjustment)
+ BranchSize += MaxAlign.value() - 4;
+
+ return BranchSize;
+}
+
+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());
+ FirstImpreciseBlock = -1;
+
+ // Measure each MBB and compute a size for the entire function.
+ unsigned FuncSize = ComputeBlockSizes(Fn);
+
+ // 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 = computeBranchSize(Fn, &MBB, Dest, MBBStartOffset);
+
+ // 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();
+ Register 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) {
+ Register CRBit = I->getOperand(0).getReg();
+ BuildMI(MBB, I, dl, TII->get(PPC::BCn)).addReg(CRBit).addImm(2);
+ } else if (I->getOpcode() == PPC::BCn) {
+ Register 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.
+ modifyAdjustment(Fn);
+ }
+
+ EverMadeChange |= MadeChange;
+ }
+
+ BlockSizes.clear();
+ return true;
+}
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