lib/Target/ARM/ARMBasicBlockInfo.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-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8
   9 #include "ARM.h"
  10 #include "ARMBaseInstrInfo.h"
  11 #include "ARMBasicBlockInfo.h"
  12 #include "ARMMachineFunctionInfo.h"
  13 #include "llvm/CodeGen/MachineBasicBlock.h"
  14 #include "llvm/CodeGen/MachineFunction.h"
  15 #include "llvm/CodeGen/MachineInstr.h"
  16 #include "llvm/CodeGen/TargetSubtargetInfo.h"
  17 #include <vector>
  18
  19 #define DEBUG_TYPE "arm-bb-utils"
  20
  21 using namespace llvm;
  22
  23 namespace llvm {
  24
  25 // mayOptimizeThumb2Instruction - Returns true if optimizeThumb2Instructions
  26 // below may shrink MI.
  27 static bool
  28 mayOptimizeThumb2Instruction(const MachineInstr *MI) {
  29   switch(MI->getOpcode()) {
  30     // optimizeThumb2Instructions.
  31     case ARM::t2LEApcrel:
  32     case ARM::t2LDRpci:
  33     // optimizeThumb2Branches.
  34     case ARM::t2B:
  35     case ARM::t2Bcc:
  36     case ARM::tBcc:
  37     // optimizeThumb2JumpTables.
  38     case ARM::t2BR_JT:
  39     case ARM::tBR_JTr:
  40       return true;
  41   }
  42   return false;
  43 }
  44
  45 void ARMBasicBlockUtils::computeBlockSize(MachineBasicBlock *MBB) {
  46   LLVM_DEBUG(dbgs() << "computeBlockSize: " << MBB->getName() << "\n");
  47   BasicBlockInfo &BBI = BBInfo[MBB->getNumber()];
  48   BBI.Size = 0;
  49   BBI.Unalign = 0;
  50   BBI.PostAlign = 0;
  51
  52   for (MachineInstr &I : *MBB) {
  53     BBI.Size += TII->getInstSizeInBytes(I);
  54     // For inline asm, getInstSizeInBytes returns a conservative estimate.
  55     // The actual size may be smaller, but still a multiple of the instr size.
  56     if (I.isInlineAsm())
  57       BBI.Unalign = isThumb ? 1 : 2;
  58     // Also consider instructions that may be shrunk later.
  59     else if (isThumb && mayOptimizeThumb2Instruction(&I))
  60       BBI.Unalign = 1;
  61   }
  62
  63   // tBR_JTr contains a .align 2 directive.
  64   if (!MBB->empty() && MBB->back().getOpcode() == ARM::tBR_JTr) {
  65     BBI.PostAlign = 2;
  66     MBB->getParent()->ensureAlignment(2);
  67   }
  68 }
  69
  70 /// getOffsetOf - Return the current offset of the specified machine instruction
  71 /// from the start of the function.  This offset changes as stuff is moved
  72 /// around inside the function.
  73 unsigned ARMBasicBlockUtils::getOffsetOf(MachineInstr *MI) const {
  74   const MachineBasicBlock *MBB = MI->getParent();
  75
  76   // The offset is composed of two things: the sum of the sizes of all MBB's
  77   // before this instruction's block, and the offset from the start of the block
  78   // it is in.
  79   unsigned Offset = BBInfo[MBB->getNumber()].Offset;
  80
  81   // Sum instructions before MI in MBB.
  82   for (MachineBasicBlock::const_iterator I = MBB->begin(); &*I != MI; ++I) {
  83     assert(I != MBB->end() && "Didn't find MI in its own basic block?");
  84     Offset += TII->getInstSizeInBytes(*I);
  85   }
  86   return Offset;
  87 }
  88
  89 /// isBBInRange - Returns true if the distance between specific MI and
  90 /// specific BB can fit in MI's displacement field.
  91 bool ARMBasicBlockUtils::isBBInRange(MachineInstr *MI,
  92                                      MachineBasicBlock *DestBB,
  93                                      unsigned MaxDisp) const {
  94   unsigned PCAdj      = isThumb ? 4 : 8;
  95   unsigned BrOffset   = getOffsetOf(MI) + PCAdj;
  96   unsigned DestOffset = BBInfo[DestBB->getNumber()].Offset;
  97
  98   LLVM_DEBUG(dbgs() << "Branch of destination " << printMBBReference(*DestBB)
  99                     << " from " << printMBBReference(*MI->getParent())
 100                     << " max delta=" << MaxDisp << " from " << getOffsetOf(MI)
 101                     << " to " << DestOffset << " offset "
 102                     << int(DestOffset - BrOffset) << "\t" << *MI);
 103
 104   if (BrOffset <= DestOffset) {
 105     // Branch before the Dest.
 106     if (DestOffset-BrOffset <= MaxDisp)
 107       return true;
 108   } else {
 109     if (BrOffset-DestOffset <= MaxDisp)
 110       return true;
 111   }
 112   return false;
 113 }
 114
 115 void ARMBasicBlockUtils::adjustBBOffsetsAfter(MachineBasicBlock *BB) {
 116   assert(BB->getParent() == &MF &&
 117          "Basic block is not a child of the current function.\n");
 118
 119   unsigned BBNum = BB->getNumber();
 120   LLVM_DEBUG(dbgs() << "Adjust block:\n"
 121              << " - name: " << BB->getName() << "\n"
 122              << " - number: " << BB->getNumber() << "\n"
 123              << " - function: " << MF.getName() << "\n"
 124              << "   - blocks: " << MF.getNumBlockIDs() << "\n");
 125
 126   for(unsigned i = BBNum + 1, e = MF.getNumBlockIDs(); i < e; ++i) {
 127     // Get the offset and known bits at the end of the layout predecessor.
 128     // Include the alignment of the current block.
 129     unsigned LogAlign = MF.getBlockNumbered(i)->getAlignment();
 130     unsigned Offset = BBInfo[i - 1].postOffset(LogAlign);
 131     unsigned KnownBits = BBInfo[i - 1].postKnownBits(LogAlign);
 132
 133     // This is where block i begins.  Stop if the offset is already correct,
 134     // and we have updated 2 blocks.  This is the maximum number of blocks
 135     // changed before calling this function.
 136     if (i > BBNum + 2 &&
 137         BBInfo[i].Offset == Offset &&
 138         BBInfo[i].KnownBits == KnownBits)
 139       break;
 140
 141     BBInfo[i].Offset = Offset;
 142     BBInfo[i].KnownBits = KnownBits;
 143   }
 144 }
 145
 146 } // end namespace llvm