1 //===--- ARMComputeBlockSize.cpp - Compute machine block sizes ------------===//
2 //
3 //                     The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 
10 #include "ARM.h"
11 #include "ARMBaseInstrInfo.h"
12 #include "ARMBasicBlockInfo.h"
13 #include "ARMMachineFunctionInfo.h"
14 #include "llvm/CodeGen/MachineBasicBlock.h"
15 #include "llvm/CodeGen/MachineFunction.h"
16 #include "llvm/CodeGen/MachineInstr.h"
17 #include "llvm/CodeGen/TargetSubtargetInfo.h"
18 #include <vector>
19 
20 using namespace llvm;
21 
22 namespace llvm {
23 
24 // mayOptimizeThumb2Instruction - Returns true if optimizeThumb2Instructions
25 // below may shrink MI.
26 static bool
27 mayOptimizeThumb2Instruction(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       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
81