mirror of
https://github.com/c64scene-ar/llvm-6502.git
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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@169651 91177308-0d34-0410-b5e6-96231b3b80d8
608 lines
21 KiB
C++
608 lines
21 KiB
C++
//===- FunctionAttrs.cpp - Pass which marks functions readnone or readonly ===//
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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, looking for functions which do not access or only read
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// non-local memory, and marking them readnone/readonly. In addition,
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// it marks function arguments (of pointer type) 'nocapture' if a call
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// to the function does not create any copies of the pointer value that
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// outlive the call. This more or less means that the pointer is only
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// dereferenced, and not returned from the function or stored in a global.
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// This pass is implemented as a bottom-up traversal of the call-graph.
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//
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//===----------------------------------------------------------------------===//
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#define DEBUG_TYPE "functionattrs"
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#include "llvm/Transforms/IPO.h"
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#include "llvm/ADT/SCCIterator.h"
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#include "llvm/ADT/SetVector.h"
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#include "llvm/ADT/SmallSet.h"
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#include "llvm/ADT/Statistic.h"
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#include "llvm/Analysis/AliasAnalysis.h"
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#include "llvm/Analysis/CallGraph.h"
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#include "llvm/Analysis/CaptureTracking.h"
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#include "llvm/CallGraphSCCPass.h"
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#include "llvm/GlobalVariable.h"
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#include "llvm/IntrinsicInst.h"
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#include "llvm/LLVMContext.h"
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#include "llvm/Support/InstIterator.h"
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using namespace llvm;
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STATISTIC(NumReadNone, "Number of functions marked readnone");
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STATISTIC(NumReadOnly, "Number of functions marked readonly");
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STATISTIC(NumNoCapture, "Number of arguments marked nocapture");
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STATISTIC(NumNoAlias, "Number of function returns marked noalias");
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namespace {
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struct FunctionAttrs : public CallGraphSCCPass {
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static char ID; // Pass identification, replacement for typeid
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FunctionAttrs() : CallGraphSCCPass(ID), AA(0) {
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initializeFunctionAttrsPass(*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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// AddReadAttrs - Deduce readonly/readnone attributes for the SCC.
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bool AddReadAttrs(const CallGraphSCC &SCC);
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// AddNoCaptureAttrs - Deduce nocapture attributes for the SCC.
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bool AddNoCaptureAttrs(const CallGraphSCC &SCC);
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// IsFunctionMallocLike - Does this function allocate new memory?
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bool IsFunctionMallocLike(Function *F,
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SmallPtrSet<Function*, 8> &) const;
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// AddNoAliasAttrs - Deduce noalias attributes for the SCC.
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bool AddNoAliasAttrs(const CallGraphSCC &SCC);
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virtual void getAnalysisUsage(AnalysisUsage &AU) const {
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AU.setPreservesCFG();
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AU.addRequired<AliasAnalysis>();
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CallGraphSCCPass::getAnalysisUsage(AU);
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}
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private:
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AliasAnalysis *AA;
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};
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}
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char FunctionAttrs::ID = 0;
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INITIALIZE_PASS_BEGIN(FunctionAttrs, "functionattrs",
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"Deduce function attributes", false, false)
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INITIALIZE_AG_DEPENDENCY(CallGraph)
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INITIALIZE_PASS_END(FunctionAttrs, "functionattrs",
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"Deduce function attributes", false, false)
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Pass *llvm::createFunctionAttrsPass() { return new FunctionAttrs(); }
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/// AddReadAttrs - Deduce readonly/readnone attributes for the SCC.
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bool FunctionAttrs::AddReadAttrs(const CallGraphSCC &SCC) {
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SmallPtrSet<Function*, 8> SCCNodes;
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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)->getFunction());
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// Check if any of the functions in the SCC read or write memory. If they
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// write memory then they can't be marked readnone or readonly.
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bool ReadsMemory = false;
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for (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end(); I != E; ++I) {
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Function *F = (*I)->getFunction();
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if (F == 0)
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// External node - may write memory. Just give up.
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return false;
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AliasAnalysis::ModRefBehavior MRB = AA->getModRefBehavior(F);
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if (MRB == AliasAnalysis::DoesNotAccessMemory)
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// Already perfect!
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continue;
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// Definitions with weak linkage may be overridden at linktime with
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// something that writes memory, so treat them like declarations.
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if (F->isDeclaration() || F->mayBeOverridden()) {
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if (!AliasAnalysis::onlyReadsMemory(MRB))
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// May write memory. Just give up.
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return false;
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ReadsMemory = true;
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continue;
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}
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// Scan the function body for instructions that may read or write memory.
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for (inst_iterator II = inst_begin(F), E = inst_end(F); II != E; ++II) {
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Instruction *I = &*II;
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// Some instructions can be ignored even if they read or write memory.
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// Detect these now, skipping to the next instruction if one is found.
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CallSite CS(cast<Value>(I));
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if (CS) {
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// Ignore calls to functions in the same SCC.
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if (CS.getCalledFunction() && SCCNodes.count(CS.getCalledFunction()))
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continue;
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AliasAnalysis::ModRefBehavior MRB = AA->getModRefBehavior(CS);
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// If the call doesn't access arbitrary memory, we may be able to
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// figure out something.
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if (AliasAnalysis::onlyAccessesArgPointees(MRB)) {
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// If the call does access argument pointees, check each argument.
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if (AliasAnalysis::doesAccessArgPointees(MRB))
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// Check whether all pointer arguments point to local memory, and
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// ignore calls that only access local memory.
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for (CallSite::arg_iterator CI = CS.arg_begin(), CE = CS.arg_end();
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CI != CE; ++CI) {
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Value *Arg = *CI;
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if (Arg->getType()->isPointerTy()) {
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AliasAnalysis::Location Loc(Arg,
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AliasAnalysis::UnknownSize,
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I->getMetadata(LLVMContext::MD_tbaa));
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if (!AA->pointsToConstantMemory(Loc, /*OrLocal=*/true)) {
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if (MRB & AliasAnalysis::Mod)
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// Writes non-local memory. Give up.
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return false;
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if (MRB & AliasAnalysis::Ref)
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// Ok, it reads non-local memory.
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ReadsMemory = true;
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}
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}
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}
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continue;
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}
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// The call could access any memory. If that includes writes, give up.
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if (MRB & AliasAnalysis::Mod)
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return false;
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// If it reads, note it.
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if (MRB & AliasAnalysis::Ref)
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ReadsMemory = true;
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continue;
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} else if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
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// Ignore non-volatile loads from local memory. (Atomic is okay here.)
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if (!LI->isVolatile()) {
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AliasAnalysis::Location Loc = AA->getLocation(LI);
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if (AA->pointsToConstantMemory(Loc, /*OrLocal=*/true))
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continue;
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}
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} else if (StoreInst *SI = dyn_cast<StoreInst>(I)) {
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// Ignore non-volatile stores to local memory. (Atomic is okay here.)
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if (!SI->isVolatile()) {
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AliasAnalysis::Location Loc = AA->getLocation(SI);
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if (AA->pointsToConstantMemory(Loc, /*OrLocal=*/true))
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continue;
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}
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} else if (VAArgInst *VI = dyn_cast<VAArgInst>(I)) {
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// Ignore vaargs on local memory.
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AliasAnalysis::Location Loc = AA->getLocation(VI);
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if (AA->pointsToConstantMemory(Loc, /*OrLocal=*/true))
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continue;
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}
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// Any remaining instructions need to be taken seriously! Check if they
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// read or write memory.
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if (I->mayWriteToMemory())
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// Writes memory. Just give up.
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return false;
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// If this instruction may read memory, remember that.
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ReadsMemory |= I->mayReadFromMemory();
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}
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}
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// Success! Functions in this SCC do not access memory, or only read memory.
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// Give them the appropriate attribute.
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bool MadeChange = false;
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for (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end(); I != E; ++I) {
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Function *F = (*I)->getFunction();
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if (F->doesNotAccessMemory())
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// Already perfect!
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continue;
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if (F->onlyReadsMemory() && ReadsMemory)
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// No change.
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continue;
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MadeChange = true;
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// Clear out any existing attributes.
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AttrBuilder B;
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B.addAttribute(Attributes::ReadOnly)
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.addAttribute(Attributes::ReadNone);
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F->removeAttribute(AttributeSet::FunctionIndex,
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Attributes::get(F->getContext(), B));
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// Add in the new attribute.
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B.clear();
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B.addAttribute(ReadsMemory ? Attributes::ReadOnly : Attributes::ReadNone);
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F->addAttribute(AttributeSet::FunctionIndex,
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Attributes::get(F->getContext(), B));
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if (ReadsMemory)
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++NumReadOnly;
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else
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++NumReadNone;
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}
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return MadeChange;
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}
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namespace {
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// For a given pointer Argument, this retains a list of Arguments of functions
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// in the same SCC that the pointer data flows into. We use this to build an
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// SCC of the arguments.
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struct ArgumentGraphNode {
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Argument *Definition;
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SmallVector<ArgumentGraphNode*, 4> Uses;
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};
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class ArgumentGraph {
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// We store pointers to ArgumentGraphNode objects, so it's important that
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// that they not move around upon insert.
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typedef std::map<Argument*, ArgumentGraphNode> ArgumentMapTy;
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ArgumentMapTy ArgumentMap;
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// There is no root node for the argument graph, in fact:
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// void f(int *x, int *y) { if (...) f(x, y); }
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// is an example where the graph is disconnected. The SCCIterator requires a
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// single entry point, so we maintain a fake ("synthetic") root node that
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// uses every node. Because the graph is directed and nothing points into
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// the root, it will not participate in any SCCs (except for its own).
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ArgumentGraphNode SyntheticRoot;
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public:
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ArgumentGraph() { SyntheticRoot.Definition = 0; }
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typedef SmallVectorImpl<ArgumentGraphNode*>::iterator iterator;
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iterator begin() { return SyntheticRoot.Uses.begin(); }
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iterator end() { return SyntheticRoot.Uses.end(); }
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ArgumentGraphNode *getEntryNode() { return &SyntheticRoot; }
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ArgumentGraphNode *operator[](Argument *A) {
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ArgumentGraphNode &Node = ArgumentMap[A];
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Node.Definition = A;
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SyntheticRoot.Uses.push_back(&Node);
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return &Node;
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}
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};
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// This tracker checks whether callees are in the SCC, and if so it does not
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// consider that a capture, instead adding it to the "Uses" list and
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// continuing with the analysis.
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struct ArgumentUsesTracker : public CaptureTracker {
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ArgumentUsesTracker(const SmallPtrSet<Function*, 8> &SCCNodes)
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: Captured(false), SCCNodes(SCCNodes) {}
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void tooManyUses() { Captured = true; }
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bool captured(Use *U) {
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CallSite CS(U->getUser());
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if (!CS.getInstruction()) { Captured = true; return true; }
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Function *F = CS.getCalledFunction();
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if (!F || !SCCNodes.count(F)) { Captured = true; return true; }
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Function::arg_iterator AI = F->arg_begin(), AE = F->arg_end();
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for (CallSite::arg_iterator PI = CS.arg_begin(), PE = CS.arg_end();
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PI != PE; ++PI, ++AI) {
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if (AI == AE) {
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assert(F->isVarArg() && "More params than args in non-varargs call");
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Captured = true;
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return true;
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}
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if (PI == U) {
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Uses.push_back(AI);
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break;
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}
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}
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assert(!Uses.empty() && "Capturing call-site captured nothing?");
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return false;
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}
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bool Captured; // True only if certainly captured (used outside our SCC).
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SmallVector<Argument*, 4> Uses; // Uses within our SCC.
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const SmallPtrSet<Function*, 8> &SCCNodes;
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};
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}
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namespace llvm {
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template<> struct GraphTraits<ArgumentGraphNode*> {
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typedef ArgumentGraphNode NodeType;
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typedef SmallVectorImpl<ArgumentGraphNode*>::iterator ChildIteratorType;
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static inline NodeType *getEntryNode(NodeType *A) { return A; }
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static inline ChildIteratorType child_begin(NodeType *N) {
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return N->Uses.begin();
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}
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static inline ChildIteratorType child_end(NodeType *N) {
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return N->Uses.end();
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}
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};
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template<> struct GraphTraits<ArgumentGraph*>
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: public GraphTraits<ArgumentGraphNode*> {
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static NodeType *getEntryNode(ArgumentGraph *AG) {
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return AG->getEntryNode();
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}
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static ChildIteratorType nodes_begin(ArgumentGraph *AG) {
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return AG->begin();
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}
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static ChildIteratorType nodes_end(ArgumentGraph *AG) {
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return AG->end();
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}
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};
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}
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/// AddNoCaptureAttrs - Deduce nocapture attributes for the SCC.
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bool FunctionAttrs::AddNoCaptureAttrs(const CallGraphSCC &SCC) {
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bool Changed = false;
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SmallPtrSet<Function*, 8> SCCNodes;
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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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Function *F = (*I)->getFunction();
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if (F && !F->isDeclaration() && !F->mayBeOverridden())
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SCCNodes.insert(F);
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}
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ArgumentGraph AG;
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AttrBuilder B;
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B.addAttribute(Attributes::NoCapture);
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// Check each function in turn, determining which pointer arguments are not
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// captured.
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for (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end(); I != E; ++I) {
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Function *F = (*I)->getFunction();
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if (F == 0)
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// External node - only a problem for arguments that we pass to it.
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continue;
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// Definitions with weak linkage may be overridden at linktime with
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// something that captures pointers, so treat them like declarations.
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if (F->isDeclaration() || F->mayBeOverridden())
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continue;
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// Functions that are readonly (or readnone) and nounwind and don't return
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// a value can't capture arguments. Don't analyze them.
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if (F->onlyReadsMemory() && F->doesNotThrow() &&
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F->getReturnType()->isVoidTy()) {
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for (Function::arg_iterator A = F->arg_begin(), E = F->arg_end();
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A != E; ++A) {
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if (A->getType()->isPointerTy() && !A->hasNoCaptureAttr()) {
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A->addAttr(Attributes::get(F->getContext(), B));
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++NumNoCapture;
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Changed = true;
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}
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}
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continue;
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}
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for (Function::arg_iterator A = F->arg_begin(), E = F->arg_end(); A!=E; ++A)
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if (A->getType()->isPointerTy() && !A->hasNoCaptureAttr()) {
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ArgumentUsesTracker Tracker(SCCNodes);
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PointerMayBeCaptured(A, &Tracker);
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if (!Tracker.Captured) {
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if (Tracker.Uses.empty()) {
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// If it's trivially not captured, mark it nocapture now.
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A->addAttr(Attributes::get(F->getContext(), B));
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++NumNoCapture;
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Changed = true;
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} else {
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// If it's not trivially captured and not trivially not captured,
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// then it must be calling into another function in our SCC. Save
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// its particulars for Argument-SCC analysis later.
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ArgumentGraphNode *Node = AG[A];
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for (SmallVectorImpl<Argument*>::iterator UI = Tracker.Uses.begin(),
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UE = Tracker.Uses.end(); UI != UE; ++UI)
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Node->Uses.push_back(AG[*UI]);
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}
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}
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// Otherwise, it's captured. Don't bother doing SCC analysis on it.
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}
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}
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// The graph we've collected is partial because we stopped scanning for
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// argument uses once we solved the argument trivially. These partial nodes
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// show up as ArgumentGraphNode objects with an empty Uses list, and for
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// these nodes the final decision about whether they capture has already been
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// made. If the definition doesn't have a 'nocapture' attribute by now, it
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// captures.
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for (scc_iterator<ArgumentGraph*> I = scc_begin(&AG), E = scc_end(&AG);
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I != E; ++I) {
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std::vector<ArgumentGraphNode*> &ArgumentSCC = *I;
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if (ArgumentSCC.size() == 1) {
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if (!ArgumentSCC[0]->Definition) continue; // synthetic root node
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// eg. "void f(int* x) { if (...) f(x); }"
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if (ArgumentSCC[0]->Uses.size() == 1 &&
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ArgumentSCC[0]->Uses[0] == ArgumentSCC[0]) {
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ArgumentSCC[0]->
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Definition->
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addAttr(Attributes::get(ArgumentSCC[0]->Definition->getContext(), B));
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++NumNoCapture;
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Changed = true;
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}
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continue;
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}
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bool SCCCaptured = false;
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for (std::vector<ArgumentGraphNode*>::iterator I = ArgumentSCC.begin(),
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E = ArgumentSCC.end(); I != E && !SCCCaptured; ++I) {
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ArgumentGraphNode *Node = *I;
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if (Node->Uses.empty()) {
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if (!Node->Definition->hasNoCaptureAttr())
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SCCCaptured = true;
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}
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}
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if (SCCCaptured) continue;
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SmallPtrSet<Argument*, 8> ArgumentSCCNodes;
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// Fill ArgumentSCCNodes with the elements of the ArgumentSCC. Used for
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// quickly looking up whether a given Argument is in this ArgumentSCC.
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for (std::vector<ArgumentGraphNode*>::iterator I = ArgumentSCC.begin(),
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E = ArgumentSCC.end(); I != E; ++I) {
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ArgumentSCCNodes.insert((*I)->Definition);
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}
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for (std::vector<ArgumentGraphNode*>::iterator I = ArgumentSCC.begin(),
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E = ArgumentSCC.end(); I != E && !SCCCaptured; ++I) {
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ArgumentGraphNode *N = *I;
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for (SmallVectorImpl<ArgumentGraphNode*>::iterator UI = N->Uses.begin(),
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UE = N->Uses.end(); UI != UE; ++UI) {
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Argument *A = (*UI)->Definition;
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if (A->hasNoCaptureAttr() || ArgumentSCCNodes.count(A))
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continue;
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SCCCaptured = true;
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break;
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}
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}
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if (SCCCaptured) continue;
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for (unsigned i = 0, e = ArgumentSCC.size(); i != e; ++i) {
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Argument *A = ArgumentSCC[i]->Definition;
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A->addAttr(Attributes::get(A->getContext(), B));
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++NumNoCapture;
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Changed = true;
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}
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}
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return Changed;
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}
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/// IsFunctionMallocLike - A function is malloc-like if it returns either null
|
|
/// or a pointer that doesn't alias any other pointer visible to the caller.
|
|
bool FunctionAttrs::IsFunctionMallocLike(Function *F,
|
|
SmallPtrSet<Function*, 8> &SCCNodes) const {
|
|
SmallSetVector<Value *, 8> FlowsToReturn;
|
|
for (Function::iterator I = F->begin(), E = F->end(); I != E; ++I)
|
|
if (ReturnInst *Ret = dyn_cast<ReturnInst>(I->getTerminator()))
|
|
FlowsToReturn.insert(Ret->getReturnValue());
|
|
|
|
for (unsigned i = 0; i != FlowsToReturn.size(); ++i) {
|
|
Value *RetVal = FlowsToReturn[i];
|
|
|
|
if (Constant *C = dyn_cast<Constant>(RetVal)) {
|
|
if (!C->isNullValue() && !isa<UndefValue>(C))
|
|
return false;
|
|
|
|
continue;
|
|
}
|
|
|
|
if (isa<Argument>(RetVal))
|
|
return false;
|
|
|
|
if (Instruction *RVI = dyn_cast<Instruction>(RetVal))
|
|
switch (RVI->getOpcode()) {
|
|
// Extend the analysis by looking upwards.
|
|
case Instruction::BitCast:
|
|
case Instruction::GetElementPtr:
|
|
FlowsToReturn.insert(RVI->getOperand(0));
|
|
continue;
|
|
case Instruction::Select: {
|
|
SelectInst *SI = cast<SelectInst>(RVI);
|
|
FlowsToReturn.insert(SI->getTrueValue());
|
|
FlowsToReturn.insert(SI->getFalseValue());
|
|
continue;
|
|
}
|
|
case Instruction::PHI: {
|
|
PHINode *PN = cast<PHINode>(RVI);
|
|
for (int i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
|
|
FlowsToReturn.insert(PN->getIncomingValue(i));
|
|
continue;
|
|
}
|
|
|
|
// Check whether the pointer came from an allocation.
|
|
case Instruction::Alloca:
|
|
break;
|
|
case Instruction::Call:
|
|
case Instruction::Invoke: {
|
|
CallSite CS(RVI);
|
|
if (CS.paramHasAttr(0, Attributes::NoAlias))
|
|
break;
|
|
if (CS.getCalledFunction() &&
|
|
SCCNodes.count(CS.getCalledFunction()))
|
|
break;
|
|
} // fall-through
|
|
default:
|
|
return false; // Did not come from an allocation.
|
|
}
|
|
|
|
if (PointerMayBeCaptured(RetVal, false, /*StoreCaptures=*/false))
|
|
return false;
|
|
}
|
|
|
|
return true;
|
|
}
|
|
|
|
/// AddNoAliasAttrs - Deduce noalias attributes for the SCC.
|
|
bool FunctionAttrs::AddNoAliasAttrs(const CallGraphSCC &SCC) {
|
|
SmallPtrSet<Function*, 8> SCCNodes;
|
|
|
|
// Fill SCCNodes with the elements of the SCC. Used for quickly
|
|
// looking up whether a given CallGraphNode is in this SCC.
|
|
for (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end(); I != E; ++I)
|
|
SCCNodes.insert((*I)->getFunction());
|
|
|
|
// Check each function in turn, determining which functions return noalias
|
|
// pointers.
|
|
for (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end(); I != E; ++I) {
|
|
Function *F = (*I)->getFunction();
|
|
|
|
if (F == 0)
|
|
// External node - skip it;
|
|
return false;
|
|
|
|
// Already noalias.
|
|
if (F->doesNotAlias(0))
|
|
continue;
|
|
|
|
// Definitions with weak linkage may be overridden at linktime, so
|
|
// treat them like declarations.
|
|
if (F->isDeclaration() || F->mayBeOverridden())
|
|
return false;
|
|
|
|
// We annotate noalias return values, which are only applicable to
|
|
// pointer types.
|
|
if (!F->getReturnType()->isPointerTy())
|
|
continue;
|
|
|
|
if (!IsFunctionMallocLike(F, SCCNodes))
|
|
return false;
|
|
}
|
|
|
|
bool MadeChange = false;
|
|
for (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end(); I != E; ++I) {
|
|
Function *F = (*I)->getFunction();
|
|
if (F->doesNotAlias(0) || !F->getReturnType()->isPointerTy())
|
|
continue;
|
|
|
|
F->setDoesNotAlias(0);
|
|
++NumNoAlias;
|
|
MadeChange = true;
|
|
}
|
|
|
|
return MadeChange;
|
|
}
|
|
|
|
bool FunctionAttrs::runOnSCC(CallGraphSCC &SCC) {
|
|
AA = &getAnalysis<AliasAnalysis>();
|
|
|
|
bool Changed = AddReadAttrs(SCC);
|
|
Changed |= AddNoCaptureAttrs(SCC);
|
|
Changed |= AddNoAliasAttrs(SCC);
|
|
return Changed;
|
|
}
|