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