1 //===-- AbstractCallSite.cpp - Implementation of abstract call sites ------===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 //
9 // This file implements abstract call sites which unify the interface for
10 // direct, indirect, and callback call sites.
11 //
12 // For more information see:
13 // https://llvm.org/devmtg/2018-10/talk-abstracts.html#talk20
14 //
15 //===----------------------------------------------------------------------===//
16
17 #include "llvm/IR/AbstractCallSite.h"
18 #include "llvm/ADT/Statistic.h"
19
20 using namespace llvm;
21
22 #define DEBUG_TYPE "abstract-call-sites"
23
24 STATISTIC(NumCallbackCallSites, "Number of callback call sites created");
25 STATISTIC(NumDirectAbstractCallSites,
26 "Number of direct abstract call sites created");
27 STATISTIC(NumInvalidAbstractCallSitesUnknownUse,
28 "Number of invalid abstract call sites created (unknown use)");
29 STATISTIC(NumInvalidAbstractCallSitesUnknownCallee,
30 "Number of invalid abstract call sites created (unknown callee)");
31 STATISTIC(NumInvalidAbstractCallSitesNoCallback,
32 "Number of invalid abstract call sites created (no callback)");
33
getCallbackUses(const CallBase & CB,SmallVectorImpl<const Use * > & CallbackUses)34 void AbstractCallSite::getCallbackUses(
35 const CallBase &CB, SmallVectorImpl<const Use *> &CallbackUses) {
36 const Function *Callee = CB.getCalledFunction();
37 if (!Callee)
38 return;
39
40 MDNode *CallbackMD = Callee->getMetadata(LLVMContext::MD_callback);
41 if (!CallbackMD)
42 return;
43
44 for (const MDOperand &Op : CallbackMD->operands()) {
45 MDNode *OpMD = cast<MDNode>(Op.get());
46 auto *CBCalleeIdxAsCM = cast<ConstantAsMetadata>(OpMD->getOperand(0));
47 uint64_t CBCalleeIdx =
48 cast<ConstantInt>(CBCalleeIdxAsCM->getValue())->getZExtValue();
49 if (CBCalleeIdx < CB.arg_size())
50 CallbackUses.push_back(CB.arg_begin() + CBCalleeIdx);
51 }
52 }
53
54 /// Create an abstract call site from a use.
AbstractCallSite(const Use * U)55 AbstractCallSite::AbstractCallSite(const Use *U)
56 : CB(dyn_cast<CallBase>(U->getUser())) {
57
58 // First handle unknown users.
59 if (!CB) {
60
61 // If the use is actually in a constant cast expression which itself
62 // has only one use, we look through the constant cast expression.
63 // This happens by updating the use @p U to the use of the constant
64 // cast expression and afterwards re-initializing CB accordingly.
65 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(U->getUser()))
66 if (CE->hasOneUse() && CE->isCast()) {
67 U = &*CE->use_begin();
68 CB = dyn_cast<CallBase>(U->getUser());
69 }
70
71 if (!CB) {
72 NumInvalidAbstractCallSitesUnknownUse++;
73 return;
74 }
75 }
76
77 // Then handle direct or indirect calls. Thus, if U is the callee of the
78 // call site CB it is not a callback and we are done.
79 if (CB->isCallee(U)) {
80 NumDirectAbstractCallSites++;
81 return;
82 }
83
84 // If we cannot identify the broker function we cannot create a callback and
85 // invalidate the abstract call site.
86 Function *Callee = CB->getCalledFunction();
87 if (!Callee) {
88 NumInvalidAbstractCallSitesUnknownCallee++;
89 CB = nullptr;
90 return;
91 }
92
93 MDNode *CallbackMD = Callee->getMetadata(LLVMContext::MD_callback);
94 if (!CallbackMD) {
95 NumInvalidAbstractCallSitesNoCallback++;
96 CB = nullptr;
97 return;
98 }
99
100 unsigned UseIdx = CB->getArgOperandNo(U);
101 MDNode *CallbackEncMD = nullptr;
102 for (const MDOperand &Op : CallbackMD->operands()) {
103 MDNode *OpMD = cast<MDNode>(Op.get());
104 auto *CBCalleeIdxAsCM = cast<ConstantAsMetadata>(OpMD->getOperand(0));
105 uint64_t CBCalleeIdx =
106 cast<ConstantInt>(CBCalleeIdxAsCM->getValue())->getZExtValue();
107 if (CBCalleeIdx != UseIdx)
108 continue;
109 CallbackEncMD = OpMD;
110 break;
111 }
112
113 if (!CallbackEncMD) {
114 NumInvalidAbstractCallSitesNoCallback++;
115 CB = nullptr;
116 return;
117 }
118
119 NumCallbackCallSites++;
120
121 assert(CallbackEncMD->getNumOperands() >= 2 && "Incomplete !callback metadata");
122
123 unsigned NumCallOperands = CB->arg_size();
124 // Skip the var-arg flag at the end when reading the metadata.
125 for (unsigned u = 0, e = CallbackEncMD->getNumOperands() - 1; u < e; u++) {
126 Metadata *OpAsM = CallbackEncMD->getOperand(u).get();
127 auto *OpAsCM = cast<ConstantAsMetadata>(OpAsM);
128 assert(OpAsCM->getType()->isIntegerTy(64) &&
129 "Malformed !callback metadata");
130
131 int64_t Idx = cast<ConstantInt>(OpAsCM->getValue())->getSExtValue();
132 assert(-1 <= Idx && Idx <= NumCallOperands &&
133 "Out-of-bounds !callback metadata index");
134
135 CI.ParameterEncoding.push_back(Idx);
136 }
137
138 if (!Callee->isVarArg())
139 return;
140
141 Metadata *VarArgFlagAsM =
142 CallbackEncMD->getOperand(CallbackEncMD->getNumOperands() - 1).get();
143 auto *VarArgFlagAsCM = cast<ConstantAsMetadata>(VarArgFlagAsM);
144 assert(VarArgFlagAsCM->getType()->isIntegerTy(1) &&
145 "Malformed !callback metadata var-arg flag");
146
147 if (VarArgFlagAsCM->getValue()->isNullValue())
148 return;
149
150 // Add all variadic arguments at the end.
151 for (unsigned u = Callee->arg_size(); u < NumCallOperands; u++)
152 CI.ParameterEncoding.push_back(u);
153 }
154