+/// \brief Compute the number of Global Variables that uses a Constant.
+static unsigned getNumGlobalVariableUses(const Constant *C) {
+ if (!C)
+ return 0;
+
+ if (isa<GlobalVariable>(C))
+ return 1;
+
+ unsigned NumUses = 0;
+ for (auto *CU : C->users())
+ NumUses += getNumGlobalVariableUses(dyn_cast<Constant>(CU));
+
+ return NumUses;
+}
+
+/// \brief Only consider global GOT equivalents if at least one user is a
+/// cstexpr inside an initializer of another global variables. Also, don't
+/// handle cstexpr inside instructions. During global variable emission,
+/// candidates are skipped and are emitted later in case at least one cstexpr
+/// isn't replaced by a PC relative GOT entry access.
+static bool isGOTEquivalentCandidate(const GlobalVariable *GV,
+ unsigned &NumGOTEquivUsers) {
+ // Global GOT equivalents are unnamed private globals with a constant
+ // pointer initializer to another global symbol. They must point to a
+ // GlobalVariable or Function, i.e., as GlobalValue.
+ if (!GV->hasUnnamedAddr() || !GV->hasInitializer() || !GV->isConstant() ||
+ !GV->isDiscardableIfUnused() || !dyn_cast<GlobalValue>(GV->getOperand(0)))
+ return false;
+
+ // To be a got equivalent, at least one of its users need to be a constant
+ // expression used by another global variable.
+ for (auto *U : GV->users())
+ NumGOTEquivUsers += getNumGlobalVariableUses(dyn_cast<Constant>(U));
+
+ return NumGOTEquivUsers > 0;
+}
+
+/// \brief Unnamed constant global variables solely contaning a pointer to
+/// another globals variable is equivalent to a GOT table entry; it contains the
+/// the address of another symbol. Optimize it and replace accesses to these
+/// "GOT equivalents" by using the GOT entry for the final global instead.
+/// Compute GOT equivalent candidates among all global variables to avoid
+/// emitting them if possible later on, after it use is replaced by a GOT entry
+/// access.
+void AsmPrinter::computeGlobalGOTEquivs(Module &M) {
+ if (!getObjFileLowering().supportIndirectSymViaGOTPCRel())
+ return;
+
+ for (const auto &G : M.globals()) {
+ unsigned NumGOTEquivUsers = 0;
+ if (!isGOTEquivalentCandidate(&G, NumGOTEquivUsers))
+ continue;
+
+ const MCSymbol *GOTEquivSym = getSymbol(&G);
+ GlobalGOTEquivs[GOTEquivSym] = std::make_pair(&G, NumGOTEquivUsers);
+ }
+}
+
+/// \brief Constant expressions using GOT equivalent globals may not be eligible
+/// for PC relative GOT entry conversion, in such cases we need to emit such
+/// globals we previously omitted in EmitGlobalVariable.
+void AsmPrinter::emitGlobalGOTEquivs() {
+ if (!getObjFileLowering().supportIndirectSymViaGOTPCRel())
+ return;
+
+ SmallVector<const GlobalVariable *, 8> FailedCandidates;
+ for (auto &I : GlobalGOTEquivs) {
+ const GlobalVariable *GV = I.second.first;
+ unsigned Cnt = I.second.second;
+ if (Cnt)
+ FailedCandidates.push_back(GV);
+ }
+ GlobalGOTEquivs.clear();
+
+ for (auto *GV : FailedCandidates)
+ EmitGlobalVariable(GV);
+}
+