llvm/lib/IR/AbstractCallSite.cpp

   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
  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.
  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 }