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external/llvm/lib/Transforms/IPO/StripSymbols.cpp
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external/llvm/lib/Transforms/IPO/StripSymbols.cpp
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//===- StripSymbols.cpp - Strip symbols and debug info from a module ------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// The StripSymbols transformation implements code stripping. Specifically, it
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// can delete:
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//
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// * names for virtual registers
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// * symbols for internal globals and functions
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// * debug information
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//
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// Note that this transformation makes code much less readable, so it should
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// only be used in situations where the 'strip' utility would be used, such as
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// reducing code size or making it harder to reverse engineer code.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/ADT/SmallPtrSet.h"
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#include "llvm/IR/Constants.h"
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#include "llvm/IR/DebugInfo.h"
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#include "llvm/IR/DerivedTypes.h"
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#include "llvm/IR/Instructions.h"
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#include "llvm/IR/Module.h"
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#include "llvm/IR/TypeFinder.h"
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#include "llvm/IR/ValueSymbolTable.h"
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#include "llvm/Pass.h"
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#include "llvm/Transforms/IPO.h"
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#include "llvm/Transforms/Utils/Local.h"
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using namespace llvm;
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namespace {
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class StripSymbols : public ModulePass {
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bool OnlyDebugInfo;
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public:
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static char ID; // Pass identification, replacement for typeid
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explicit StripSymbols(bool ODI = false)
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: ModulePass(ID), OnlyDebugInfo(ODI) {
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initializeStripSymbolsPass(*PassRegistry::getPassRegistry());
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}
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bool runOnModule(Module &M) override;
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void getAnalysisUsage(AnalysisUsage &AU) const override {
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AU.setPreservesAll();
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}
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};
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class StripNonDebugSymbols : public ModulePass {
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public:
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static char ID; // Pass identification, replacement for typeid
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explicit StripNonDebugSymbols()
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: ModulePass(ID) {
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initializeStripNonDebugSymbolsPass(*PassRegistry::getPassRegistry());
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}
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bool runOnModule(Module &M) override;
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void getAnalysisUsage(AnalysisUsage &AU) const override {
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AU.setPreservesAll();
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}
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};
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class StripDebugDeclare : public ModulePass {
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public:
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static char ID; // Pass identification, replacement for typeid
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explicit StripDebugDeclare()
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: ModulePass(ID) {
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initializeStripDebugDeclarePass(*PassRegistry::getPassRegistry());
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}
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bool runOnModule(Module &M) override;
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void getAnalysisUsage(AnalysisUsage &AU) const override {
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AU.setPreservesAll();
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}
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};
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class StripDeadDebugInfo : public ModulePass {
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public:
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static char ID; // Pass identification, replacement for typeid
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explicit StripDeadDebugInfo()
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: ModulePass(ID) {
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initializeStripDeadDebugInfoPass(*PassRegistry::getPassRegistry());
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}
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bool runOnModule(Module &M) override;
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void getAnalysisUsage(AnalysisUsage &AU) const override {
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AU.setPreservesAll();
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}
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};
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}
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char StripSymbols::ID = 0;
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INITIALIZE_PASS(StripSymbols, "strip",
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"Strip all symbols from a module", false, false)
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ModulePass *llvm::createStripSymbolsPass(bool OnlyDebugInfo) {
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return new StripSymbols(OnlyDebugInfo);
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}
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char StripNonDebugSymbols::ID = 0;
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INITIALIZE_PASS(StripNonDebugSymbols, "strip-nondebug",
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"Strip all symbols, except dbg symbols, from a module",
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false, false)
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ModulePass *llvm::createStripNonDebugSymbolsPass() {
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return new StripNonDebugSymbols();
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}
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char StripDebugDeclare::ID = 0;
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INITIALIZE_PASS(StripDebugDeclare, "strip-debug-declare",
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"Strip all llvm.dbg.declare intrinsics", false, false)
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ModulePass *llvm::createStripDebugDeclarePass() {
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return new StripDebugDeclare();
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}
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char StripDeadDebugInfo::ID = 0;
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INITIALIZE_PASS(StripDeadDebugInfo, "strip-dead-debug-info",
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"Strip debug info for unused symbols", false, false)
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ModulePass *llvm::createStripDeadDebugInfoPass() {
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return new StripDeadDebugInfo();
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}
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/// OnlyUsedBy - Return true if V is only used by Usr.
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static bool OnlyUsedBy(Value *V, Value *Usr) {
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for (User *U : V->users())
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if (U != Usr)
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return false;
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return true;
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}
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static void RemoveDeadConstant(Constant *C) {
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assert(C->use_empty() && "Constant is not dead!");
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SmallPtrSet<Constant*, 4> Operands;
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for (Value *Op : C->operands())
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if (OnlyUsedBy(Op, C))
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Operands.insert(cast<Constant>(Op));
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if (GlobalVariable *GV = dyn_cast<GlobalVariable>(C)) {
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if (!GV->hasLocalLinkage()) return; // Don't delete non-static globals.
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GV->eraseFromParent();
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}
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else if (!isa<Function>(C))
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if (isa<CompositeType>(C->getType()))
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C->destroyConstant();
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// If the constant referenced anything, see if we can delete it as well.
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for (Constant *O : Operands)
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RemoveDeadConstant(O);
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}
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// Strip the symbol table of its names.
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//
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static void StripSymtab(ValueSymbolTable &ST, bool PreserveDbgInfo) {
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for (ValueSymbolTable::iterator VI = ST.begin(), VE = ST.end(); VI != VE; ) {
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Value *V = VI->getValue();
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++VI;
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if (!isa<GlobalValue>(V) || cast<GlobalValue>(V)->hasLocalLinkage()) {
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if (!PreserveDbgInfo || !V->getName().startswith("llvm.dbg"))
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// Set name to "", removing from symbol table!
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V->setName("");
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}
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}
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}
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// Strip any named types of their names.
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static void StripTypeNames(Module &M, bool PreserveDbgInfo) {
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TypeFinder StructTypes;
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StructTypes.run(M, false);
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for (unsigned i = 0, e = StructTypes.size(); i != e; ++i) {
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StructType *STy = StructTypes[i];
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if (STy->isLiteral() || STy->getName().empty()) continue;
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if (PreserveDbgInfo && STy->getName().startswith("llvm.dbg"))
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continue;
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STy->setName("");
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}
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}
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/// Find values that are marked as llvm.used.
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static void findUsedValues(GlobalVariable *LLVMUsed,
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SmallPtrSetImpl<const GlobalValue*> &UsedValues) {
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if (!LLVMUsed) return;
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UsedValues.insert(LLVMUsed);
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ConstantArray *Inits = cast<ConstantArray>(LLVMUsed->getInitializer());
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for (unsigned i = 0, e = Inits->getNumOperands(); i != e; ++i)
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if (GlobalValue *GV =
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dyn_cast<GlobalValue>(Inits->getOperand(i)->stripPointerCasts()))
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UsedValues.insert(GV);
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}
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/// StripSymbolNames - Strip symbol names.
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static bool StripSymbolNames(Module &M, bool PreserveDbgInfo) {
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SmallPtrSet<const GlobalValue*, 8> llvmUsedValues;
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findUsedValues(M.getGlobalVariable("llvm.used"), llvmUsedValues);
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findUsedValues(M.getGlobalVariable("llvm.compiler.used"), llvmUsedValues);
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for (Module::global_iterator I = M.global_begin(), E = M.global_end();
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I != E; ++I) {
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if (I->hasLocalLinkage() && llvmUsedValues.count(&*I) == 0)
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if (!PreserveDbgInfo || !I->getName().startswith("llvm.dbg"))
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I->setName(""); // Internal symbols can't participate in linkage
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}
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for (Function &I : M) {
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if (I.hasLocalLinkage() && llvmUsedValues.count(&I) == 0)
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if (!PreserveDbgInfo || !I.getName().startswith("llvm.dbg"))
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I.setName(""); // Internal symbols can't participate in linkage
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if (auto *Symtab = I.getValueSymbolTable())
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StripSymtab(*Symtab, PreserveDbgInfo);
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}
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// Remove all names from types.
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StripTypeNames(M, PreserveDbgInfo);
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return true;
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}
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bool StripSymbols::runOnModule(Module &M) {
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if (skipModule(M))
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return false;
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bool Changed = false;
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Changed |= StripDebugInfo(M);
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if (!OnlyDebugInfo)
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Changed |= StripSymbolNames(M, false);
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return Changed;
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}
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bool StripNonDebugSymbols::runOnModule(Module &M) {
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if (skipModule(M))
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return false;
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return StripSymbolNames(M, true);
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}
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bool StripDebugDeclare::runOnModule(Module &M) {
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if (skipModule(M))
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return false;
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Function *Declare = M.getFunction("llvm.dbg.declare");
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std::vector<Constant*> DeadConstants;
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if (Declare) {
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while (!Declare->use_empty()) {
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CallInst *CI = cast<CallInst>(Declare->user_back());
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Value *Arg1 = CI->getArgOperand(0);
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Value *Arg2 = CI->getArgOperand(1);
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assert(CI->use_empty() && "llvm.dbg intrinsic should have void result");
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CI->eraseFromParent();
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if (Arg1->use_empty()) {
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if (Constant *C = dyn_cast<Constant>(Arg1))
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DeadConstants.push_back(C);
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else
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RecursivelyDeleteTriviallyDeadInstructions(Arg1);
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}
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if (Arg2->use_empty())
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if (Constant *C = dyn_cast<Constant>(Arg2))
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DeadConstants.push_back(C);
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}
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Declare->eraseFromParent();
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}
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while (!DeadConstants.empty()) {
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Constant *C = DeadConstants.back();
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DeadConstants.pop_back();
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if (GlobalVariable *GV = dyn_cast<GlobalVariable>(C)) {
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if (GV->hasLocalLinkage())
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RemoveDeadConstant(GV);
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} else
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RemoveDeadConstant(C);
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}
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return true;
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}
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/// Remove any debug info for global variables/functions in the given module for
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/// which said global variable/function no longer exists (i.e. is null).
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///
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/// Debugging information is encoded in llvm IR using metadata. This is designed
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/// such a way that debug info for symbols preserved even if symbols are
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/// optimized away by the optimizer. This special pass removes debug info for
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/// such symbols.
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bool StripDeadDebugInfo::runOnModule(Module &M) {
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if (skipModule(M))
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return false;
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bool Changed = false;
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LLVMContext &C = M.getContext();
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// Find all debug info in F. This is actually overkill in terms of what we
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// want to do, but we want to try and be as resilient as possible in the face
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// of potential debug info changes by using the formal interfaces given to us
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// as much as possible.
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DebugInfoFinder F;
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F.processModule(M);
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// For each compile unit, find the live set of global variables/functions and
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// replace the current list of potentially dead global variables/functions
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// with the live list.
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SmallVector<Metadata *, 64> LiveGlobalVariables;
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DenseSet<DIGlobalVariableExpression *> VisitedSet;
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std::set<DIGlobalVariableExpression *> LiveGVs;
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for (GlobalVariable &GV : M.globals()) {
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SmallVector<DIGlobalVariableExpression *, 1> GVEs;
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GV.getDebugInfo(GVEs);
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for (auto *GVE : GVEs)
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LiveGVs.insert(GVE);
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}
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std::set<DICompileUnit *> LiveCUs;
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// Any CU referenced from a subprogram is live.
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for (DISubprogram *SP : F.subprograms()) {
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if (SP->getUnit())
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LiveCUs.insert(SP->getUnit());
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}
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bool HasDeadCUs = false;
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for (DICompileUnit *DIC : F.compile_units()) {
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// Create our live global variable list.
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bool GlobalVariableChange = false;
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for (auto *DIG : DIC->getGlobalVariables()) {
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if (DIG->getExpression() && DIG->getExpression()->isConstant())
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LiveGVs.insert(DIG);
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// Make sure we only visit each global variable only once.
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if (!VisitedSet.insert(DIG).second)
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continue;
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// If a global variable references DIG, the global variable is live.
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if (LiveGVs.count(DIG))
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LiveGlobalVariables.push_back(DIG);
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else
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GlobalVariableChange = true;
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}
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if (!LiveGlobalVariables.empty())
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LiveCUs.insert(DIC);
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else if (!LiveCUs.count(DIC))
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HasDeadCUs = true;
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// If we found dead global variables, replace the current global
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// variable list with our new live global variable list.
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if (GlobalVariableChange) {
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DIC->replaceGlobalVariables(MDTuple::get(C, LiveGlobalVariables));
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Changed = true;
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}
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// Reset lists for the next iteration.
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LiveGlobalVariables.clear();
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}
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if (HasDeadCUs) {
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// Delete the old node and replace it with a new one
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NamedMDNode *NMD = M.getOrInsertNamedMetadata("llvm.dbg.cu");
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NMD->clearOperands();
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if (!LiveCUs.empty()) {
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for (DICompileUnit *CU : LiveCUs)
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NMD->addOperand(CU);
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}
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Changed = true;
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}
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return Changed;
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}
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