1 //===- LibCallAliasAnalysis.cpp - Implement AliasAnalysis for libcalls ----===//
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 // This file implements the LibCallAliasAnalysis class.
11 //
12 //===----------------------------------------------------------------------===//
13
14 #include "llvm/Analysis/LibCallAliasAnalysis.h"
15 #include "llvm/Analysis/LibCallSemantics.h"
16 #include "llvm/Analysis/Passes.h"
17 #include "llvm/IR/Function.h"
18 #include "llvm/Pass.h"
19 using namespace llvm;
20
21 // Register this pass...
22 char LibCallAliasAnalysis::ID = 0;
23 INITIALIZE_AG_PASS(LibCallAliasAnalysis, AliasAnalysis, "libcall-aa",
24 "LibCall Alias Analysis", false, true, false)
25
createLibCallAliasAnalysisPass(LibCallInfo * LCI)26 FunctionPass *llvm::createLibCallAliasAnalysisPass(LibCallInfo *LCI) {
27 return new LibCallAliasAnalysis(LCI);
28 }
29
~LibCallAliasAnalysis()30 LibCallAliasAnalysis::~LibCallAliasAnalysis() {
31 delete LCI;
32 }
33
getAnalysisUsage(AnalysisUsage & AU) const34 void LibCallAliasAnalysis::getAnalysisUsage(AnalysisUsage &AU) const {
35 AliasAnalysis::getAnalysisUsage(AU);
36 AU.setPreservesAll(); // Does not transform code
37 }
38
runOnFunction(Function & F)39 bool LibCallAliasAnalysis::runOnFunction(Function &F) {
40 // set up super class
41 InitializeAliasAnalysis(this, &F.getParent()->getDataLayout());
42 return false;
43 }
44
45 /// AnalyzeLibCallDetails - Given a call to a function with the specified
46 /// LibCallFunctionInfo, see if we can improve the mod/ref footprint of the call
47 /// vs the specified pointer/size.
48 AliasAnalysis::ModRefResult
AnalyzeLibCallDetails(const LibCallFunctionInfo * FI,ImmutableCallSite CS,const Location & Loc)49 LibCallAliasAnalysis::AnalyzeLibCallDetails(const LibCallFunctionInfo *FI,
50 ImmutableCallSite CS,
51 const Location &Loc) {
52 // If we have a function, check to see what kind of mod/ref effects it
53 // has. Start by including any info globally known about the function.
54 AliasAnalysis::ModRefResult MRInfo = FI->UniversalBehavior;
55 if (MRInfo == NoModRef) return MRInfo;
56
57 // If that didn't tell us that the function is 'readnone', check to see
58 // if we have detailed info and if 'P' is any of the locations we know
59 // about.
60 const LibCallFunctionInfo::LocationMRInfo *Details = FI->LocationDetails;
61 if (Details == nullptr)
62 return MRInfo;
63
64 // If the details array is of the 'DoesNot' kind, we only know something if
65 // the pointer is a match for one of the locations in 'Details'. If we find a
66 // match, we can prove some interactions cannot happen.
67 //
68 if (FI->DetailsType == LibCallFunctionInfo::DoesNot) {
69 // Find out if the pointer refers to a known location.
70 for (unsigned i = 0; Details[i].LocationID != ~0U; ++i) {
71 const LibCallLocationInfo &LocInfo =
72 LCI->getLocationInfo(Details[i].LocationID);
73 LibCallLocationInfo::LocResult Res = LocInfo.isLocation(CS, Loc);
74 if (Res != LibCallLocationInfo::Yes) continue;
75
76 // If we find a match against a location that we 'do not' interact with,
77 // learn this info into MRInfo.
78 return ModRefResult(MRInfo & ~Details[i].MRInfo);
79 }
80 return MRInfo;
81 }
82
83 // If the details are of the 'DoesOnly' sort, we know something if the pointer
84 // is a match for one of the locations in 'Details'. Also, if we can prove
85 // that the pointers is *not* one of the locations in 'Details', we know that
86 // the call is NoModRef.
87 assert(FI->DetailsType == LibCallFunctionInfo::DoesOnly);
88
89 // Find out if the pointer refers to a known location.
90 bool NoneMatch = true;
91 for (unsigned i = 0; Details[i].LocationID != ~0U; ++i) {
92 const LibCallLocationInfo &LocInfo =
93 LCI->getLocationInfo(Details[i].LocationID);
94 LibCallLocationInfo::LocResult Res = LocInfo.isLocation(CS, Loc);
95 if (Res == LibCallLocationInfo::No) continue;
96
97 // If we don't know if this pointer points to the location, then we have to
98 // assume it might alias in some case.
99 if (Res == LibCallLocationInfo::Unknown) {
100 NoneMatch = false;
101 continue;
102 }
103
104 // If we know that this pointer definitely is pointing into the location,
105 // merge in this information.
106 return ModRefResult(MRInfo & Details[i].MRInfo);
107 }
108
109 // If we found that the pointer is guaranteed to not match any of the
110 // locations in our 'DoesOnly' rule, then we know that the pointer must point
111 // to some other location. Since the libcall doesn't mod/ref any other
112 // locations, return NoModRef.
113 if (NoneMatch)
114 return NoModRef;
115
116 // Otherwise, return any other info gained so far.
117 return MRInfo;
118 }
119
120 // getModRefInfo - Check to see if the specified callsite can clobber the
121 // specified memory object.
122 //
123 AliasAnalysis::ModRefResult
getModRefInfo(ImmutableCallSite CS,const Location & Loc)124 LibCallAliasAnalysis::getModRefInfo(ImmutableCallSite CS,
125 const Location &Loc) {
126 ModRefResult MRInfo = ModRef;
127
128 // If this is a direct call to a function that LCI knows about, get the
129 // information about the runtime function.
130 if (LCI) {
131 if (const Function *F = CS.getCalledFunction()) {
132 if (const LibCallFunctionInfo *FI = LCI->getFunctionInfo(F)) {
133 MRInfo = ModRefResult(MRInfo & AnalyzeLibCallDetails(FI, CS, Loc));
134 if (MRInfo == NoModRef) return NoModRef;
135 }
136 }
137 }
138
139 // The AliasAnalysis base class has some smarts, lets use them.
140 return (ModRefResult)(MRInfo | AliasAnalysis::getModRefInfo(CS, Loc));
141 }
142