lib/Target/ARM/ARMComputeBlockSize.cpp

   1 //===--- ARMComputeBlockSize.cpp - Compute machine 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 using namespace llvm;
  20
  21 namespace llvm {
  22
  23 // mayOptimizeThumb2Instruction - Returns true if optimizeThumb2Instructions
  24 // below may shrink MI.
  25 static bool
  26 mayOptimizeThumb2Instruction(const MachineInstr *MI) {
  27   switch(MI->getOpcode()) {
  28     // optimizeThumb2Instructions.
  29     case ARM::t2LEApcrel:
  30     case ARM::t2LDRpci:
  31     // optimizeThumb2Branches.
  32     case ARM::t2B:
  33     case ARM::t2Bcc:
  34     case ARM::tBcc:
  35     // optimizeThumb2JumpTables.
  36     case ARM::t2BR_JT:
  37     case ARM::tBR_JTr:
  38       return true;
  39   }
  40   return false;
  41 }
  42
  43 void computeBlockSize(MachineFunction *MF, MachineBasicBlock *MBB,
  44                       BasicBlockInfo &BBI) {
  45   const ARMBaseInstrInfo *TII =
  46     static_cast<const ARMBaseInstrInfo *>(MF->getSubtarget().getInstrInfo());
  47   bool isThumb = MF->getInfo<ARMFunctionInfo>()->isThumbFunction();
  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 std::vector<BasicBlockInfo> computeAllBlockSizes(MachineFunction *MF) {
  71   std::vector<BasicBlockInfo> BBInfo;
  72   BBInfo.resize(MF->getNumBlockIDs());
  73
  74   for (MachineBasicBlock &MBB : *MF)
  75     computeBlockSize(MF, &MBB, BBInfo[MBB.getNumber()]);
  76
  77   return BBInfo;
  78 }
  79
  80 } // end namespace llvm