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"
19using namespace llvm;
20
21// Register this pass...
22char LibCallAliasAnalysis::ID = 0;
23INITIALIZE_AG_PASS(LibCallAliasAnalysis, AliasAnalysis, "libcall-aa",
24                   "LibCall Alias Analysis", false, true, false)
25
26FunctionPass *llvm::createLibCallAliasAnalysisPass(LibCallInfo *LCI) {
27  return new LibCallAliasAnalysis(LCI);
28}
29
30LibCallAliasAnalysis::~LibCallAliasAnalysis() {
31  delete LCI;
32}
33
34void 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.
44AliasAnalysis::ModRefResult
45LibCallAliasAnalysis::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 == nullptr)
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//
119AliasAnalysis::ModRefResult
120LibCallAliasAnalysis::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