1 //===- llvm/CodeGen/GlobalISel/InstructionSelect.cpp - InstructionSelect ---==//
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 /// \file
10 /// This file implements the InstructionSelect class.
11 //===----------------------------------------------------------------------===//
12 
13 #include "llvm/CodeGen/GlobalISel/InstructionSelect.h"
14 #include "llvm/ADT/PostOrderIterator.h"
15 #include "llvm/ADT/Twine.h"
16 #include "llvm/CodeGen/GlobalISel/InstructionSelector.h"
17 #include "llvm/CodeGen/MachineRegisterInfo.h"
18 #include "llvm/IR/Function.h"
19 #include "llvm/Support/CommandLine.h"
20 #include "llvm/Support/Debug.h"
21 #include "llvm/Target/TargetSubtargetInfo.h"
22 
23 #define DEBUG_TYPE "instruction-select"
24 
25 using namespace llvm;
26 
27 char InstructionSelect::ID = 0;
28 INITIALIZE_PASS(InstructionSelect, DEBUG_TYPE,
29                 "Select target instructions out of generic instructions",
30                 false, false);
31 
32 InstructionSelect::InstructionSelect() : MachineFunctionPass(ID) {
33   initializeInstructionSelectPass(*PassRegistry::getPassRegistry());
34 }
35 
36 static void reportSelectionError(const MachineInstr &MI, const Twine &Message) {
37   const MachineFunction &MF = *MI.getParent()->getParent();
38   std::string ErrStorage;
39   raw_string_ostream Err(ErrStorage);
40   Err << Message << ":\nIn function: " << MF.getName() << '\n' << MI << '\n';
41   report_fatal_error(Err.str());
42 }
43 
44 bool InstructionSelect::runOnMachineFunction(MachineFunction &MF) {
45   DEBUG(dbgs() << "Selecting function: " << MF.getName() << '\n');
46 
47   const InstructionSelector *ISel = MF.getSubtarget().getInstructionSelector();
48   assert(ISel && "Cannot work without InstructionSelector");
49 
50   // FIXME: freezeReservedRegs is now done in IRTranslator, but there are many
51   // other MF/MFI fields we need to initialize.
52 
53 #ifndef NDEBUG
54   // FIXME: We could introduce new blocks and will need to fix the outer loop.
55   // Until then, keep track of the number of blocks to assert that we don't.
56   const size_t NumBlocks = MF.size();
57 #endif
58 
59   for (MachineBasicBlock *MBB : post_order(&MF)) {
60     for (MachineBasicBlock::reverse_iterator MII = MBB->rbegin(),
61                                              End = MBB->rend();
62          MII != End;) {
63       MachineInstr &MI = *MII++;
64       DEBUG(dbgs() << "Selecting: " << MI << '\n');
65       if (!ISel->select(MI))
66         reportSelectionError(MI, "Cannot select");
67       // FIXME: It would be nice to dump all inserted instructions.  It's not
68       // obvious how, esp. considering select() can insert after MI.
69     }
70   }
71 
72   assert(MF.size() == NumBlocks && "Inserting blocks is not supported yet");
73 
74   // Check that we did select everything. Do this separately to make sure we
75   // didn't miss any newly inserted instructions.
76   // FIXME: This (and other checks) should move into a verifier, predicated on
77   // a "post-isel" MachineFunction property. That would also let us selectively
78   // enable it depending on build configuration.
79   for (MachineBasicBlock &MBB : MF) {
80     for (MachineInstr &MI : MBB) {
81       if (isPreISelGenericOpcode(MI.getOpcode())) {
82         reportSelectionError(
83             MI, "Generic instruction survived instruction selection");
84       }
85     }
86   }
87 
88   // Now that selection is complete, there are no more generic vregs.
89   // FIXME: We're still discussing what to do with the vreg->size map:
90   // it's somewhat redundant (with the def MIs type size), but having to
91   // examine MIs is also awkward.  Another alternative is to track the type on
92   // the vreg instead, but that's not ideal either, because it's saying that
93   // vregs have types, which they really don't. But then again, LLT is just
94   // a size and a "shape": it's probably the same information as regbank info.
95   MF.getRegInfo().clearVirtRegSizes();
96 
97   // FIXME: Should we accurately track changes?
98   return true;
99 }
100