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//===- DeadTypeElimination.cpp - Eliminate unused types for symbol table --===//
//
// This pass is used to cleanup the output of GCC. It eliminate names for types
// that are unused in the entire translation unit, using the FindUsedTypes pass.
//
//===----------------------------------------------------------------------===//
#include "llvm/Transforms/IPO.h"
#include "llvm/Analysis/FindUsedTypes.h"
#include "llvm/Module.h"
#include "llvm/SymbolTable.h"
#include "llvm/DerivedTypes.h"
#include "Support/Statistic.h"
namespace {
struct DTE : public Pass {
// doPassInitialization - For this pass, it removes global symbol table
// entries for primitive types. These are never used for linking in GCC and
// they make the output uglier to look at, so we nuke them.
//
// Also, initialize instance variables.
//
bool run(Module &M);
// getAnalysisUsage - This function needs FindUsedTypes to do its job...
//
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.addRequired<FindUsedTypes>();
}
};
RegisterOpt<DTE> X("deadtypeelim", "Dead Type Elimination");
Statistic<>
NumKilled("deadtypeelim", "Number of unused typenames removed from symtab");
}
Pass *createDeadTypeEliminationPass() {
return new DTE();
}
// ShouldNukSymtabEntry - Return true if this module level symbol table entry
// should be eliminated.
//
static inline bool ShouldNukeSymtabEntry(const std::pair<std::string,Value*>&E){
// Nuke all names for primitive types!
if (cast<Type>(E.second)->isPrimitiveType()) return true;
// Nuke all pointers to primitive types as well...
if (const PointerType *PT = dyn_cast<PointerType>(E.second))
if (PT->getElementType()->isPrimitiveType()) return true;
return false;
}
// run - For this pass, it removes global symbol table entries for primitive
// types. These are never used for linking in GCC and they make the output
// uglier to look at, so we nuke them. Also eliminate types that are never used
// in the entire program as indicated by FindUsedTypes.
//
bool DTE::run(Module &M) {
bool Changed = false;
SymbolTable &ST = M.getSymbolTable();
const std::set<const Type *> &UsedTypes =
getAnalysis<FindUsedTypes>().getTypes();
// Check the symbol table for superfluous type entries...
//
// Grab the 'type' plane of the module symbol...
SymbolTable::iterator STI = ST.find(Type::TypeTy);
if (STI != ST.end()) {
// Loop over all entries in the type plane...
SymbolTable::VarMap &Plane = STI->second;
for (SymbolTable::VarMap::iterator PI = Plane.begin(); PI != Plane.end();)
// If this entry should be unconditionally removed, or if we detect that
// the type is not used, remove it.
if (ShouldNukeSymtabEntry(*PI) ||
!UsedTypes.count(cast<Type>(PI->second))) {
SymbolTable::VarMap::iterator PJ = PI++;
Plane.erase(PJ);
++NumKilled;
Changed = true;
} else {
++PI;
}
}
return Changed;
}
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