llvm/llvm/lib/Target/PowerPC/PPCBranchSelector.cpp

//===-- 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>
usingnamespacellvm;

#define DEBUG_TYPE …

STATISTIC(NumExpanded, "Number of branches expanded to long format");
STATISTIC(NumPrefixed, "Number of prefixed instructions");
STATISTIC(NumPrefixedAligned,
          "Number of prefixed instructions that have been aligned");

namespace {
  struct PPCBSel : public MachineFunctionPass { … };
  char PPCBSel::ID = …;
}

INITIALIZE_PASS(…)

/// createPPCBranchSelectionPass - returns an instance of the Branch Selection
/// Pass
///
FunctionPass *llvm::createPPCBranchSelectionPass() { … }

/// In order to make MBB aligned, we need to add an adjustment value to the
/// original Offset.
unsigned PPCBSel::GetAlignmentAdjustment(MachineBasicBlock &MBB,
                                         unsigned Offset) { … }

/// 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) { … }

/// Measure each MBB and compute a size for the entire function.
unsigned PPCBSel::ComputeBlockSizes(MachineFunction &Fn) { … }

/// Modify the basic block align adjustment.
void PPCBSel::modifyAdjustment(MachineFunction &Fn) { … }

/// 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) { … }

bool PPCBSel::runOnMachineFunction(MachineFunction &Fn) { … }