1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
|
//===-- MSP430BranchSelector.cpp - Emit long conditional branches ---------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file contains a pass that scans a machine function to determine which
// conditional branches need more than 10 bits of displacement to reach their
// target basic block. It does this in two passes; a calculation of basic block
// positions pass, and a branch pseudo op to machine branch opcode pass. This
// pass should be run last, just before the assembly printer.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "msp430-branch-select"
#include "MSP430.h"
#include "MSP430InstrInfo.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Support/MathExtras.h"
using namespace llvm;
STATISTIC(NumExpanded, "Number of branches expanded to long format");
namespace {
struct MSP430BSel : public MachineFunctionPass {
static char ID;
MSP430BSel() : MachineFunctionPass(ID) {}
/// BlockSizes - The sizes of the basic blocks in the function.
std::vector<unsigned> BlockSizes;
virtual bool runOnMachineFunction(MachineFunction &Fn);
virtual const char *getPassName() const {
return "MSP430 Branch Selector";
}
};
char MSP430BSel::ID = 0;
}
/// createMSP430BranchSelectionPass - returns an instance of the Branch
/// Selection Pass
///
FunctionPass *llvm::createMSP430BranchSelectionPass() {
return new MSP430BSel();
}
bool MSP430BSel::runOnMachineFunction(MachineFunction &Fn) {
const MSP430InstrInfo *TII =
static_cast<const MSP430InstrInfo*>(Fn.getTarget().getInstrInfo());
// Give the blocks of the function a dense, in-order, numbering.
Fn.RenumberBlocks();
BlockSizes.resize(Fn.getNumBlockIDs());
// Measure each MBB and compute a size for the entire function.
unsigned FuncSize = 0;
for (MachineFunction::iterator MFI = Fn.begin(), E = Fn.end(); MFI != E;
++MFI) {
MachineBasicBlock *MBB = MFI;
unsigned BlockSize = 0;
for (MachineBasicBlock::iterator MBBI = MBB->begin(), EE = MBB->end();
MBBI != EE; ++MBBI)
BlockSize += TII->GetInstSizeInBytes(MBBI);
BlockSizes[MBB->getNumber()] = BlockSize;
FuncSize += BlockSize;
}
// If the entire function is smaller than the displacement of a branch field,
// we know we don't need to shrink any branches in this function. This is a
// common case.
if (FuncSize < (1 << 9)) {
BlockSizes.clear();
return false;
}
// For each conditional branch, if the offset to its destination is larger
// than the offset field allows, transform it into a long branch sequence
// like this:
// short branch:
// bCC MBB
// long branch:
// b!CC $PC+6
// b MBB
//
bool MadeChange = true;
bool EverMadeChange = false;
while (MadeChange) {
// Iteratively expand branches until we reach a fixed point.
MadeChange = false;
for (MachineFunction::iterator MFI = Fn.begin(), E = Fn.end(); MFI != E;
++MFI) {
MachineBasicBlock &MBB = *MFI;
unsigned MBBStartOffset = 0;
for (MachineBasicBlock::iterator I = MBB.begin(), E = MBB.end();
I != E; ++I) {
if ((I->getOpcode() != MSP430::JCC || I->getOperand(0).isImm()) &&
I->getOpcode() != MSP430::JMP) {
MBBStartOffset += TII->GetInstSizeInBytes(I);
continue;
}
// Determine the offset from the current branch to the destination
// block.
MachineBasicBlock *Dest = I->getOperand(0).getMBB();
int BranchSize;
if (Dest->getNumber() <= MBB.getNumber()) {
// If this is a backwards branch, the delta is the offset from the
// start of this block to this branch, plus the sizes of all blocks
// from this block to the dest.
BranchSize = MBBStartOffset;
for (unsigned i = Dest->getNumber(), e = MBB.getNumber(); i != e; ++i)
BranchSize += BlockSizes[i];
} else {
// Otherwise, add the size of the blocks between this block and the
// dest to the number of bytes left in this block.
BranchSize = -MBBStartOffset;
for (unsigned i = MBB.getNumber(), e = Dest->getNumber(); i != e; ++i)
BranchSize += BlockSizes[i];
}
// If this branch is in range, ignore it.
if (isInt<10>(BranchSize)) {
MBBStartOffset += 2;
continue;
}
// Otherwise, we have to expand it to a long branch.
unsigned NewSize;
MachineInstr *OldBranch = I;
DebugLoc dl = OldBranch->getDebugLoc();
if (I->getOpcode() == MSP430::JMP) {
NewSize = 4;
} else {
// The BCC operands are:
// 0. MSP430 branch predicate
// 1. Target MBB
SmallVector<MachineOperand, 1> Cond;
Cond.push_back(I->getOperand(1));
// Jump over the uncond branch inst (i.e. $+6) on opposite condition.
TII->ReverseBranchCondition(Cond);
BuildMI(MBB, I, dl, TII->get(MSP430::JCC))
.addImm(4).addOperand(Cond[0]);
NewSize = 6;
}
// Uncond branch to the real destination.
I = BuildMI(MBB, I, dl, TII->get(MSP430::Bi)).addMBB(Dest);
// Remove the old branch from the function.
OldBranch->eraseFromParent();
// Remember that this instruction is NewSize bytes, increase the size of the
// block by NewSize-2, remember to iterate.
BlockSizes[MBB.getNumber()] += NewSize-2;
MBBStartOffset += NewSize;
++NumExpanded;
MadeChange = true;
}
}
EverMadeChange |= MadeChange;
}
BlockSizes.clear();
return true;
}
|
