146 lines · cpp
1//===--- ARMBasicBlockInfo.cpp - Utilities for block sizes ---------------===//2//3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.4// See https://llvm.org/LICENSE.txt for license information.5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception6//7//===----------------------------------------------------------------------===//8 9#include "ARMBasicBlockInfo.h"10#include "ARM.h"11#include "ARMBaseInstrInfo.h"12#include "llvm/CodeGen/MachineBasicBlock.h"13#include "llvm/CodeGen/MachineFunction.h"14#include "llvm/CodeGen/MachineInstr.h"15#include "llvm/CodeGen/TargetSubtargetInfo.h"16#include "llvm/Support/Debug.h"17 18#define DEBUG_TYPE "arm-bb-utils"19 20using namespace llvm;21 22namespace llvm {23 24// mayOptimizeThumb2Instruction - Returns true if optimizeThumb2Instructions25// below may shrink MI.26static bool27mayOptimizeThumb2Instruction(const MachineInstr *MI) {28 switch(MI->getOpcode()) {29 // optimizeThumb2Instructions.30 case ARM::t2LEApcrel:31 case ARM::t2LDRpci:32 // optimizeThumb2Branches.33 case ARM::t2B:34 case ARM::t2Bcc:35 case ARM::tBcc:36 // optimizeThumb2JumpTables.37 case ARM::t2BR_JT:38 case ARM::tBR_JTr:39 return true;40 }41 return false;42}43 44void ARMBasicBlockUtils::computeBlockSize(MachineBasicBlock *MBB) {45 LLVM_DEBUG(dbgs() << "computeBlockSize: " << MBB->getName() << "\n");46 BasicBlockInfo &BBI = BBInfo[MBB->getNumber()];47 BBI.Size = 0;48 BBI.Unalign = 0;49 BBI.PostAlign = Align(1);50 51 for (MachineInstr &I : *MBB) {52 BBI.Size += TII->getInstSizeInBytes(I);53 // For inline asm, getInstSizeInBytes returns a conservative estimate.54 // The actual size may be smaller, but still a multiple of the instr size.55 if (I.isInlineAsm())56 BBI.Unalign = isThumb ? 1 : 2;57 // Also consider instructions that may be shrunk later.58 else if (isThumb && mayOptimizeThumb2Instruction(&I))59 BBI.Unalign = 1;60 }61 62 // tBR_JTr contains a .align 2 directive.63 if (!MBB->empty() && MBB->back().getOpcode() == ARM::tBR_JTr) {64 BBI.PostAlign = Align(4);65 MBB->getParent()->ensureAlignment(Align(4));66 }67}68 69/// getOffsetOf - Return the current offset of the specified machine instruction70/// from the start of the function. This offset changes as stuff is moved71/// around inside the function.72unsigned ARMBasicBlockUtils::getOffsetOf(MachineInstr *MI) const {73 const MachineBasicBlock *MBB = MI->getParent();74 75 // The offset is composed of two things: the sum of the sizes of all MBB's76 // before this instruction's block, and the offset from the start of the block77 // it is in.78 unsigned Offset = BBInfo[MBB->getNumber()].Offset;79 80 // Sum instructions before MI in MBB.81 for (MachineBasicBlock::const_iterator I = MBB->begin(); &*I != MI; ++I) {82 assert(I != MBB->end() && "Didn't find MI in its own basic block?");83 Offset += TII->getInstSizeInBytes(*I);84 }85 return Offset;86}87 88/// isBBInRange - Returns true if the distance between specific MI and89/// specific BB can fit in MI's displacement field.90bool ARMBasicBlockUtils::isBBInRange(MachineInstr *MI,91 MachineBasicBlock *DestBB,92 unsigned MaxDisp) const {93 unsigned PCAdj = isThumb ? 4 : 8;94 unsigned BrOffset = getOffsetOf(MI) + PCAdj;95 unsigned DestOffset = BBInfo[DestBB->getNumber()].Offset;96 97 LLVM_DEBUG(dbgs() << "Branch of destination " << printMBBReference(*DestBB)98 << " from " << printMBBReference(*MI->getParent())99 << " max delta=" << MaxDisp << " from " << getOffsetOf(MI)100 << " to " << DestOffset << " offset "101 << int(DestOffset - BrOffset) << "\t" << *MI);102 103 if (BrOffset <= DestOffset) {104 // Branch before the Dest.105 if (DestOffset-BrOffset <= MaxDisp)106 return true;107 } else {108 if (BrOffset-DestOffset <= MaxDisp)109 return true;110 }111 return false;112}113 114void ARMBasicBlockUtils::adjustBBOffsetsAfter(MachineBasicBlock *BB) {115 assert(BB->getParent() == &MF &&116 "Basic block is not a child of the current function.\n");117 118 unsigned BBNum = BB->getNumber();119 LLVM_DEBUG(dbgs() << "Adjust block:\n"120 << " - name: " << BB->getName() << "\n"121 << " - number: " << BB->getNumber() << "\n"122 << " - function: " << MF.getName() << "\n"123 << " - blocks: " << MF.getNumBlockIDs() << "\n");124 125 for(unsigned i = BBNum + 1, e = MF.getNumBlockIDs(); i < e; ++i) {126 // Get the offset and known bits at the end of the layout predecessor.127 // Include the alignment of the current block.128 const Align Align = MF.getBlockNumbered(i)->getAlignment();129 const unsigned Offset = BBInfo[i - 1].postOffset(Align);130 const unsigned KnownBits = BBInfo[i - 1].postKnownBits(Align);131 132 // This is where block i begins. Stop if the offset is already correct,133 // and we have updated 2 blocks. This is the maximum number of blocks134 // changed before calling this function.135 if (i > BBNum + 2 &&136 BBInfo[i].Offset == Offset &&137 BBInfo[i].KnownBits == KnownBits)138 break;139 140 BBInfo[i].Offset = Offset;141 BBInfo[i].KnownBits = KnownBits;142 }143}144 145} // end namespace llvm146