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//===- AddReadAttrs.cpp - Pass which marks functions readnone or readonly -===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements a simple interprocedural pass which walks the
// call-graph, looking for functions which do not access or only read
// non-local memory, and marking them readnone/readonly. It implements
// this as a bottom-up traversal of the call-graph.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "addreadattrs"
#include "llvm/Transforms/IPO.h"
#include "llvm/CallGraphSCCPass.h"
#include "llvm/Instructions.h"
#include "llvm/Analysis/CallGraph.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/InstIterator.h"
using namespace llvm;
STATISTIC(NumReadNone, "Number of functions marked readnone");
STATISTIC(NumReadOnly, "Number of functions marked readonly");
namespace {
struct VISIBILITY_HIDDEN AddReadAttrs : public CallGraphSCCPass {
static char ID; // Pass identification, replacement for typeid
AddReadAttrs() : CallGraphSCCPass(&ID) {}
// runOnSCC - Analyze the SCC, performing the transformation if possible.
bool runOnSCC(const std::vector<CallGraphNode *> &SCC);
};
}
char AddReadAttrs::ID = 0;
static RegisterPass<AddReadAttrs>
X("addreadattrs", "Mark functions readnone/readonly");
Pass *llvm::createAddReadAttrsPass() { return new AddReadAttrs(); }
bool AddReadAttrs::runOnSCC(const std::vector<CallGraphNode *> &SCC) {
CallGraph &CG = getAnalysis<CallGraph>();
// Check if any of the functions in the SCC read or write memory.
// If they write memory then just give up.
bool ReadsMemory = false;
for (unsigned i = 0, e = SCC.size(); i != e; ++i) {
Function *F = SCC[i]->getFunction();
if (F == 0)
// External node - may write memory.
return false;
if (F->doesNotAccessMemory())
// Already perfect!
continue;
// Definitions with weak linkage may be overridden at linktime with
// something that writes memory, so treat them like declarations.
if (F->isDeclaration() || F->hasWeakLinkage()) {
if (!F->onlyReadsMemory())
// May write memory.
return false;
ReadsMemory = true;
continue;
}
// Scan the function body for instructions that may read or write memory.
for (inst_iterator II = inst_begin(F), E = inst_end(F); II != E; ++II) {
CallSite CS = CallSite::get(&*II);
// Ignore calls to functions in the same SCC.
if (CS.getInstruction() &&
std::find(SCC.begin(), SCC.end(), CG[CS.getCalledFunction()]) !=
SCC.end())
continue;
if (II->mayWriteToMemory())
return false;
ReadsMemory |= II->mayReadFromMemory();
}
}
// Success! Functions in this SCC do not access memory, or only read memory.
// Give them the appropriate attribute.
bool MadeChange = false;
for (unsigned i = 0, e = SCC.size(); i != e; ++i) {
Function *F = SCC[i]->getFunction();
if (F->doesNotAccessMemory())
// Already perfect!
continue;
if (F->onlyReadsMemory() && ReadsMemory)
// No change.
continue;
MadeChange = true;
// Clear out any existing attributes.
F->removeParamAttr(0, ParamAttr::ReadOnly | ParamAttr::ReadNone);
// Add in the new attribute.
F->addParamAttr(0, ReadsMemory ? ParamAttr::ReadOnly : ParamAttr::ReadNone);
if (ReadsMemory)
NumReadOnly++;
else
NumReadNone++;
}
return MadeChange;
}
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