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
|
//===- AddReadAttrs.cpp - Pass which marks functions readnone or readonly -===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements a simple interprocedural pass which walks the
// call-graph, looking for functions which do not access or only read
// non-local memory, and marking them readnone/readonly. It implements
// this as a bottom-up traversal of the call-graph.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "addreadattrs"
#include "llvm/Transforms/IPO.h"
#include "llvm/CallGraphSCCPass.h"
#include "llvm/Instructions.h"
#include "llvm/Analysis/CallGraph.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/InstIterator.h"
using namespace llvm;
STATISTIC(NumReadNone, "Number of functions marked readnone");
STATISTIC(NumReadOnly, "Number of functions marked readonly");
namespace {
struct VISIBILITY_HIDDEN AddReadAttrs : public CallGraphSCCPass {
static char ID; // Pass identification, replacement for typeid
AddReadAttrs() : CallGraphSCCPass(&ID) {}
// runOnSCC - Analyze the SCC, performing the transformation if possible.
bool runOnSCC(const std::vector<CallGraphNode *> &SCC);
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.setPreservesCFG();
CallGraphSCCPass::getAnalysisUsage(AU);
}
};
}
char AddReadAttrs::ID = 0;
static RegisterPass<AddReadAttrs>
X("addreadattrs", "Mark functions readnone/readonly");
Pass *llvm::createAddReadAttrsPass() { return new AddReadAttrs(); }
bool AddReadAttrs::runOnSCC(const std::vector<CallGraphNode *> &SCC) {
SmallPtrSet<CallGraphNode *, 8> SCCNodes;
CallGraph &CG = getAnalysis<CallGraph>();
// Fill SCCNodes with the elements of the SCC. Used for quickly
// looking up whether a given CallGraphNode is in this SCC.
for (unsigned i = 0, e = SCC.size(); i != e; ++i)
SCCNodes.insert(SCC[i]);
// Check if any of the functions in the SCC read or write memory. If they
// write memory then they can't be marked readnone or readonly.
bool ReadsMemory = false;
for (unsigned i = 0, e = SCC.size(); i != e; ++i) {
Function *F = SCC[i]->getFunction();
if (F == 0)
// External node - may write memory. Just give up.
return false;
if (F->doesNotAccessMemory())
// Already perfect!
continue;
// Definitions with weak linkage may be overridden at linktime with
// something that writes memory, so treat them like declarations.
if (F->isDeclaration() || F->mayBeOverridden()) {
if (!F->onlyReadsMemory())
// May write memory. Just give up.
return false;
ReadsMemory = true;
continue;
}
// Scan the function body for instructions that may read or write memory.
for (inst_iterator II = inst_begin(F), E = inst_end(F); II != E; ++II) {
CallSite CS = CallSite::get(&*II);
// Ignore calls to functions in the same SCC.
if (CS.getInstruction() && SCCNodes.count(CG[CS.getCalledFunction()]))
continue;
if (II->mayWriteToMemory())
// Writes memory. Just give up.
return false;
ReadsMemory |= II->mayReadFromMemory();
}
}
// Success! Functions in this SCC do not access memory, or only read memory.
// Give them the appropriate attribute.
bool MadeChange = false;
for (unsigned i = 0, e = SCC.size(); i != e; ++i) {
Function *F = SCC[i]->getFunction();
if (F->doesNotAccessMemory())
// Already perfect!
continue;
if (F->onlyReadsMemory() && ReadsMemory)
// No change.
continue;
MadeChange = true;
// Clear out any existing attributes.
F->removeAttribute(~0, Attribute::ReadOnly | Attribute::ReadNone);
// Add in the new attribute.
F->addAttribute(~0, ReadsMemory ? Attribute::ReadOnly : Attribute::ReadNone);
if (ReadsMemory)
NumReadOnly++;
else
NumReadNone++;
}
return MadeChange;
}
|
