1 //===- LibCallAliasAnalysis.cpp - Implement AliasAnalysis for libcalls ----===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file implements the LibCallAliasAnalysis class.
12 //===----------------------------------------------------------------------===//
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"
21 // Register this pass...
22 char LibCallAliasAnalysis::ID = 0;
23 INITIALIZE_AG_PASS(LibCallAliasAnalysis, AliasAnalysis, "libcall-aa",
24 "LibCall Alias Analysis", false, true, false)
26 FunctionPass *llvm::createLibCallAliasAnalysisPass(LibCallInfo *LCI) {
27 return new LibCallAliasAnalysis(LCI);
30 LibCallAliasAnalysis::~LibCallAliasAnalysis() {
34 void LibCallAliasAnalysis::getAnalysisUsage(AnalysisUsage &AU) const {
35 AliasAnalysis::getAnalysisUsage(AU);
36 AU.setPreservesAll(); // Does not transform code
39 bool LibCallAliasAnalysis::runOnFunction(Function &F) {
41 InitializeAliasAnalysis(this, &F.getParent()->getDataLayout());
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.
49 LibCallAliasAnalysis::AnalyzeLibCallDetails(const LibCallFunctionInfo *FI,
51 const MemoryLocation &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 ModRefInfo MRInfo = FI->UniversalBehavior;
55 if (MRInfo == MRI_NoModRef)
58 // If that didn't tell us that the function is 'readnone', check to see
59 // if we have detailed info and if 'P' is any of the locations we know
61 const LibCallFunctionInfo::LocationMRInfo *Details = FI->LocationDetails;
62 if (Details == nullptr)
65 // If the details array is of the 'DoesNot' kind, we only know something if
66 // the pointer is a match for one of the locations in 'Details'. If we find a
67 // match, we can prove some interactions cannot happen.
69 if (FI->DetailsType == LibCallFunctionInfo::DoesNot) {
70 // Find out if the pointer refers to a known location.
71 for (unsigned i = 0; Details[i].LocationID != ~0U; ++i) {
72 const LibCallLocationInfo &LocInfo =
73 LCI->getLocationInfo(Details[i].LocationID);
74 LibCallLocationInfo::LocResult Res = LocInfo.isLocation(CS, Loc);
75 if (Res != LibCallLocationInfo::Yes) continue;
77 // If we find a match against a location that we 'do not' interact with,
78 // learn this info into MRInfo.
79 return ModRefInfo(MRInfo & ~Details[i].MRInfo);
84 // If the details are of the 'DoesOnly' sort, we know something if the pointer
85 // is a match for one of the locations in 'Details'. Also, if we can prove
86 // that the pointers is *not* one of the locations in 'Details', we know that
87 // the call is MRI_NoModRef.
88 assert(FI->DetailsType == LibCallFunctionInfo::DoesOnly);
90 // Find out if the pointer refers to a known location.
91 bool NoneMatch = true;
92 for (unsigned i = 0; Details[i].LocationID != ~0U; ++i) {
93 const LibCallLocationInfo &LocInfo =
94 LCI->getLocationInfo(Details[i].LocationID);
95 LibCallLocationInfo::LocResult Res = LocInfo.isLocation(CS, Loc);
96 if (Res == LibCallLocationInfo::No) continue;
98 // If we don't know if this pointer points to the location, then we have to
99 // assume it might alias in some case.
100 if (Res == LibCallLocationInfo::Unknown) {
105 // If we know that this pointer definitely is pointing into the location,
106 // merge in this information.
107 return ModRefInfo(MRInfo & Details[i].MRInfo);
110 // If we found that the pointer is guaranteed to not match any of the
111 // locations in our 'DoesOnly' rule, then we know that the pointer must point
112 // to some other location. Since the libcall doesn't mod/ref any other
113 // locations, return MRI_NoModRef.
117 // Otherwise, return any other info gained so far.
121 // getModRefInfo - Check to see if the specified callsite can clobber the
122 // specified memory object.
124 ModRefInfo LibCallAliasAnalysis::getModRefInfo(ImmutableCallSite CS,
125 const MemoryLocation &Loc) {
126 ModRefInfo MRInfo = MRI_ModRef;
128 // If this is a direct call to a function that LCI knows about, get the
129 // information about the runtime function.
131 if (const Function *F = CS.getCalledFunction()) {
132 if (const LibCallFunctionInfo *FI = LCI->getFunctionInfo(F)) {
133 MRInfo = ModRefInfo(MRInfo & AnalyzeLibCallDetails(FI, CS, Loc));
134 if (MRInfo == MRI_NoModRef)
140 // The AliasAnalysis base class has some smarts, lets use them.
141 return (ModRefInfo)(MRInfo | AliasAnalysis::getModRefInfo(CS, Loc));