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CallGraph. This makes the CallGraph a totally generic analysis object that is the container for the graph data structure and the primary interface for querying and manipulating it. The pass logic is separated into its own class. For compatibility reasons, the pass provides wrapper methods for most of the methods on CallGraph -- they all just forward. This will allow the new pass manager infrastructure to provide its own analysis pass that constructs the same CallGraph object and makes it available. The idea is that in the new pass manager, the analysis pass's 'run' method returns a concrete analysis 'result'. Here, that result is a 'CallGraph'. The 'run' method will typically do only minimal work, deferring much of the work into the implementation of the result object in order to be lazy about computing things, but when (like DomTree) there is *some* up-front computation, the analysis does it prior to handing the result back to the querying pass. I know some of this is fairly ugly. I'm happy to change it around if folks can suggest a cleaner interim state, but there is going to be some amount of unavoidable ugliness during the transition period. The good thing is that this is very limited and will naturally go away when the old pass infrastructure goes away. It won't hang around to bother us later. Next up is the initial new-PM-style call graph analysis. =] git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@195722 91177308-0d34-0410-b5e6-96231b3b80d8
259 lines
9.7 KiB
C++
259 lines
9.7 KiB
C++
//===- PruneEH.cpp - Pass which deletes unused exception handlers ---------===//
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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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// This file implements a simple interprocedural pass which walks the
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// call-graph, turning invoke instructions into calls, iff the callee cannot
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// throw an exception, and marking functions 'nounwind' if they cannot throw.
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// It implements this as a bottom-up traversal of the call-graph.
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//
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//===----------------------------------------------------------------------===//
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#define DEBUG_TYPE "prune-eh"
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#include "llvm/Transforms/IPO.h"
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#include "llvm/ADT/SmallPtrSet.h"
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#include "llvm/ADT/SmallVector.h"
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#include "llvm/ADT/Statistic.h"
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#include "llvm/Analysis/CallGraph.h"
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#include "llvm/Analysis/CallGraphSCCPass.h"
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#include "llvm/IR/Constants.h"
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#include "llvm/IR/Function.h"
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#include "llvm/IR/Instructions.h"
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#include "llvm/IR/IntrinsicInst.h"
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#include "llvm/IR/LLVMContext.h"
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#include "llvm/Support/CFG.h"
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#include <algorithm>
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using namespace llvm;
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STATISTIC(NumRemoved, "Number of invokes removed");
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STATISTIC(NumUnreach, "Number of noreturn calls optimized");
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namespace {
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struct PruneEH : public CallGraphSCCPass {
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static char ID; // Pass identification, replacement for typeid
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PruneEH() : CallGraphSCCPass(ID) {
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initializePruneEHPass(*PassRegistry::getPassRegistry());
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}
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// runOnSCC - Analyze the SCC, performing the transformation if possible.
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bool runOnSCC(CallGraphSCC &SCC);
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bool SimplifyFunction(Function *F);
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void DeleteBasicBlock(BasicBlock *BB);
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};
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}
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char PruneEH::ID = 0;
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INITIALIZE_PASS_BEGIN(PruneEH, "prune-eh",
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"Remove unused exception handling info", false, false)
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INITIALIZE_PASS_DEPENDENCY(CallGraphWrapperPass)
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INITIALIZE_PASS_END(PruneEH, "prune-eh",
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"Remove unused exception handling info", false, false)
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Pass *llvm::createPruneEHPass() { return new PruneEH(); }
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bool PruneEH::runOnSCC(CallGraphSCC &SCC) {
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SmallPtrSet<CallGraphNode *, 8> SCCNodes;
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CallGraph &CG = getAnalysis<CallGraphWrapperPass>().getCallGraph();
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bool MadeChange = false;
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// Fill SCCNodes with the elements of the SCC. Used for quickly
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// looking up whether a given CallGraphNode is in this SCC.
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for (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end(); I != E; ++I)
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SCCNodes.insert(*I);
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// First pass, scan all of the functions in the SCC, simplifying them
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// according to what we know.
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for (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end(); I != E; ++I)
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if (Function *F = (*I)->getFunction())
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MadeChange |= SimplifyFunction(F);
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// Next, check to see if any callees might throw or if there are any external
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// functions in this SCC: if so, we cannot prune any functions in this SCC.
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// Definitions that are weak and not declared non-throwing might be
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// overridden at linktime with something that throws, so assume that.
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// If this SCC includes the unwind instruction, we KNOW it throws, so
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// obviously the SCC might throw.
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//
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bool SCCMightUnwind = false, SCCMightReturn = false;
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for (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end();
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(!SCCMightUnwind || !SCCMightReturn) && I != E; ++I) {
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Function *F = (*I)->getFunction();
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if (F == 0) {
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SCCMightUnwind = true;
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SCCMightReturn = true;
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} else if (F->isDeclaration() || F->mayBeOverridden()) {
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SCCMightUnwind |= !F->doesNotThrow();
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SCCMightReturn |= !F->doesNotReturn();
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} else {
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bool CheckUnwind = !SCCMightUnwind && !F->doesNotThrow();
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bool CheckReturn = !SCCMightReturn && !F->doesNotReturn();
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if (!CheckUnwind && !CheckReturn)
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continue;
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// Check to see if this function performs an unwind or calls an
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// unwinding function.
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for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB) {
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if (CheckUnwind && isa<ResumeInst>(BB->getTerminator())) {
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// Uses unwind / resume!
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SCCMightUnwind = true;
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} else if (CheckReturn && isa<ReturnInst>(BB->getTerminator())) {
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SCCMightReturn = true;
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}
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// Invoke instructions don't allow unwinding to continue, so we are
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// only interested in call instructions.
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if (CheckUnwind && !SCCMightUnwind)
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for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I)
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if (CallInst *CI = dyn_cast<CallInst>(I)) {
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if (CI->doesNotThrow()) {
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// This call cannot throw.
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} else if (Function *Callee = CI->getCalledFunction()) {
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CallGraphNode *CalleeNode = CG[Callee];
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// If the callee is outside our current SCC then we may
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// throw because it might.
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if (!SCCNodes.count(CalleeNode)) {
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SCCMightUnwind = true;
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break;
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}
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} else {
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// Indirect call, it might throw.
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SCCMightUnwind = true;
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break;
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}
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}
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if (SCCMightUnwind && SCCMightReturn) break;
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}
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}
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}
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// If the SCC doesn't unwind or doesn't throw, note this fact.
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if (!SCCMightUnwind || !SCCMightReturn)
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for (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end(); I != E; ++I) {
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AttrBuilder NewAttributes;
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if (!SCCMightUnwind)
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NewAttributes.addAttribute(Attribute::NoUnwind);
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if (!SCCMightReturn)
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NewAttributes.addAttribute(Attribute::NoReturn);
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Function *F = (*I)->getFunction();
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const AttributeSet &PAL = F->getAttributes().getFnAttributes();
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const AttributeSet &NPAL = AttributeSet::get(
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F->getContext(), AttributeSet::FunctionIndex, NewAttributes);
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if (PAL != NPAL) {
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MadeChange = true;
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F->addAttributes(AttributeSet::FunctionIndex, NPAL);
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}
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}
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for (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end(); I != E; ++I) {
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// Convert any invoke instructions to non-throwing functions in this node
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// into call instructions with a branch. This makes the exception blocks
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// dead.
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if (Function *F = (*I)->getFunction())
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MadeChange |= SimplifyFunction(F);
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}
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return MadeChange;
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}
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// SimplifyFunction - Given information about callees, simplify the specified
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// function if we have invokes to non-unwinding functions or code after calls to
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// no-return functions.
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bool PruneEH::SimplifyFunction(Function *F) {
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bool MadeChange = false;
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for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB) {
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if (InvokeInst *II = dyn_cast<InvokeInst>(BB->getTerminator()))
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if (II->doesNotThrow()) {
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SmallVector<Value*, 8> Args(II->op_begin(), II->op_end() - 3);
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// Insert a call instruction before the invoke.
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CallInst *Call = CallInst::Create(II->getCalledValue(), Args, "", II);
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Call->takeName(II);
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Call->setCallingConv(II->getCallingConv());
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Call->setAttributes(II->getAttributes());
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Call->setDebugLoc(II->getDebugLoc());
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// Anything that used the value produced by the invoke instruction
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// now uses the value produced by the call instruction. Note that we
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// do this even for void functions and calls with no uses so that the
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// callgraph edge is updated.
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II->replaceAllUsesWith(Call);
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BasicBlock *UnwindBlock = II->getUnwindDest();
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UnwindBlock->removePredecessor(II->getParent());
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// Insert a branch to the normal destination right before the
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// invoke.
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BranchInst::Create(II->getNormalDest(), II);
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// Finally, delete the invoke instruction!
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BB->getInstList().pop_back();
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// If the unwind block is now dead, nuke it.
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if (pred_begin(UnwindBlock) == pred_end(UnwindBlock))
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DeleteBasicBlock(UnwindBlock); // Delete the new BB.
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++NumRemoved;
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MadeChange = true;
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}
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for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; )
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if (CallInst *CI = dyn_cast<CallInst>(I++))
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if (CI->doesNotReturn() && !isa<UnreachableInst>(I)) {
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// This call calls a function that cannot return. Insert an
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// unreachable instruction after it and simplify the code. Do this
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// by splitting the BB, adding the unreachable, then deleting the
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// new BB.
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BasicBlock *New = BB->splitBasicBlock(I);
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// Remove the uncond branch and add an unreachable.
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BB->getInstList().pop_back();
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new UnreachableInst(BB->getContext(), BB);
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DeleteBasicBlock(New); // Delete the new BB.
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MadeChange = true;
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++NumUnreach;
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break;
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}
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}
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return MadeChange;
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}
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/// DeleteBasicBlock - remove the specified basic block from the program,
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/// updating the callgraph to reflect any now-obsolete edges due to calls that
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/// exist in the BB.
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void PruneEH::DeleteBasicBlock(BasicBlock *BB) {
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assert(pred_begin(BB) == pred_end(BB) && "BB is not dead!");
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CallGraph &CG = getAnalysis<CallGraphWrapperPass>().getCallGraph();
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CallGraphNode *CGN = CG[BB->getParent()];
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for (BasicBlock::iterator I = BB->end(), E = BB->begin(); I != E; ) {
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--I;
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if (CallInst *CI = dyn_cast<CallInst>(I)) {
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if (!isa<IntrinsicInst>(I))
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CGN->removeCallEdgeFor(CI);
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} else if (InvokeInst *II = dyn_cast<InvokeInst>(I))
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CGN->removeCallEdgeFor(II);
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if (!I->use_empty())
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I->replaceAllUsesWith(UndefValue::get(I->getType()));
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}
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// Get the list of successors of this block.
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std::vector<BasicBlock*> Succs(succ_begin(BB), succ_end(BB));
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for (unsigned i = 0, e = Succs.size(); i != e; ++i)
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Succs[i]->removePredecessor(BB);
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BB->eraseFromParent();
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}
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