#include "llvm/Module.h"
#include "llvm/Pass.h"
#include "llvm/ADT/Statistic.h"
+#include "llvm/Analysis/InlineCost.h"
#include "llvm/Transforms/Utils/Cloning.h"
-#include "llvm/Support/Compiler.h"
+#include "llvm/Support/CallSite.h"
+#include "llvm/ADT/DenseSet.h"
#include <map>
using namespace llvm;
STATISTIC(numSpecialized, "Number of specialized functions created");
+STATISTIC(numReplaced, "Number of callers replaced by specialization");
-// Call must be used at least occasionally
-static const int CallsMin = 5;
-
-// Must have 10% of calls having the same constant to specialize on
-static const double ConstValPercent = .1;
+// Maximum number of arguments markable interested
+static const int MaxInterests = 6;
namespace {
- class VISIBILITY_HIDDEN PartSpec : public ModulePass {
- void scanForInterest(Function&, SmallVector<int, 6>&);
- void replaceUsersFor(Function&, int, Constant*, Function*);
+ typedef SmallVector<int, MaxInterests> InterestingArgVector;
+ class PartSpec : public ModulePass {
+ void scanForInterest(Function&, InterestingArgVector&);
int scanDistribution(Function&, int, std::map<Constant*, int>&);
+ InlineCostAnalyzer CA;
public :
static char ID; // Pass identification, replacement for typeid
- PartSpec() : ModulePass((intptr_t)&ID) {}
+ PartSpec() : ModulePass(ID) {
+ initializePartSpecPass(*PassRegistry::getPassRegistry());
+ }
bool runOnModule(Module &M);
};
}
char PartSpec::ID = 0;
-static RegisterPass<PartSpec>
-X("partialspecialization", "Partial Specialization");
+INITIALIZE_PASS(PartSpec, "partialspecialization",
+ "Partial Specialization", false, false)
+
+// Specialize F by replacing the arguments (keys) in replacements with the
+// constants (values). Replace all calls to F with those constants with
+// a call to the specialized function. Returns the specialized function
+static Function*
+SpecializeFunction(Function* F,
+ ValueToValueMapTy& replacements) {
+ // arg numbers of deleted arguments
+ DenseMap<unsigned, const Argument*> deleted;
+ for (ValueToValueMapTy::iterator
+ repb = replacements.begin(), repe = replacements.end();
+ repb != repe; ++repb) {
+ Argument const *arg = cast<const Argument>(repb->first);
+ deleted[arg->getArgNo()] = arg;
+ }
+
+ Function* NF = CloneFunction(F, replacements,
+ /*ModuleLevelChanges=*/false);
+ NF->setLinkage(GlobalValue::InternalLinkage);
+ F->getParent()->getFunctionList().push_back(NF);
+
+ // FIXME: Specialized versions getting the same constants should also get
+ // the same name. That way, specializations for public functions can be
+ // marked linkonce_odr and reused across modules.
+
+ for (Value::use_iterator ii = F->use_begin(), ee = F->use_end();
+ ii != ee; ) {
+ Value::use_iterator i = ii;
+ ++ii;
+ User *U = *i;
+ CallSite CS(U);
+ if (CS) {
+ if (CS.getCalledFunction() == F) {
+ SmallVector<Value*, 6> args;
+ // Assemble the non-specialized arguments for the updated callsite.
+ // In the process, make sure that the specialized arguments are
+ // constant and match the specialization. If that's not the case,
+ // this callsite needs to call the original or some other
+ // specialization; don't change it here.
+ CallSite::arg_iterator as = CS.arg_begin(), ae = CS.arg_end();
+ for (CallSite::arg_iterator ai = as; ai != ae; ++ai) {
+ DenseMap<unsigned, const Argument*>::iterator delit = deleted.find(
+ std::distance(as, ai));
+ if (delit == deleted.end())
+ args.push_back(cast<Value>(ai));
+ else {
+ Constant *ci = dyn_cast<Constant>(ai);
+ if (!(ci && ci == replacements[delit->second]))
+ goto next_use;
+ }
+ }
+ Value* NCall;
+ if (CallInst *CI = dyn_cast<CallInst>(U)) {
+ NCall = CallInst::Create(NF, args.begin(), args.end(),
+ CI->getName(), CI);
+ cast<CallInst>(NCall)->setTailCall(CI->isTailCall());
+ cast<CallInst>(NCall)->setCallingConv(CI->getCallingConv());
+ } else {
+ InvokeInst *II = cast<InvokeInst>(U);
+ NCall = InvokeInst::Create(NF, II->getNormalDest(),
+ II->getUnwindDest(),
+ args.begin(), args.end(),
+ II->getName(), II);
+ cast<InvokeInst>(NCall)->setCallingConv(II->getCallingConv());
+ }
+ CS.getInstruction()->replaceAllUsesWith(NCall);
+ CS.getInstruction()->eraseFromParent();
+ ++numReplaced;
+ }
+ }
+ next_use:;
+ }
+ return NF;
+}
+
bool PartSpec::runOnModule(Module &M) {
bool Changed = false;
for (Module::iterator I = M.begin(); I != M.end(); ++I) {
Function &F = *I;
- if (F.isDeclaration()) continue;
- SmallVector<int, 6> interestingArgs;
+ if (F.isDeclaration() || F.mayBeOverridden()) continue;
+ InterestingArgVector interestingArgs;
scanForInterest(F, interestingArgs);
// Find the first interesting Argument that we can specialize on
bool breakOuter = false;
for (unsigned int x = 0; !breakOuter && x < interestingArgs.size(); ++x) {
std::map<Constant*, int> distribution;
- int total = scanDistribution(F, interestingArgs[x], distribution);
- if (total > CallsMin)
- for (std::map<Constant*, int>::iterator ii = distribution.begin(),
- ee = distribution.end(); ii != ee; ++ii)
- if (total > ii->second && ii->first &&
- ii->second > total * ConstValPercent) {
- Function* NF = CloneFunction(&F);
- NF->setLinkage(GlobalValue::InternalLinkage);
- M.getFunctionList().push_back(NF);
- replaceUsersFor(F, interestingArgs[x], ii->first, NF);
- breakOuter = true;
- Changed = true;
- }
+ scanDistribution(F, interestingArgs[x], distribution);
+ for (std::map<Constant*, int>::iterator ii = distribution.begin(),
+ ee = distribution.end(); ii != ee; ++ii) {
+ // The distribution map might have an entry for NULL (i.e., one or more
+ // callsites were passing a non-constant there). We allow that to
+ // happen so that we can see whether any callsites pass a non-constant;
+ // if none do and the function is internal, we might have an opportunity
+ // to kill the original function.
+ if (!ii->first) continue;
+ int bonus = ii->second;
+ SmallVector<unsigned, 1> argnos;
+ argnos.push_back(interestingArgs[x]);
+ InlineCost cost = CA.getSpecializationCost(&F, argnos);
+ // FIXME: If this is the last constant entry, and no non-constant
+ // entries exist, and the target function is internal, the cost should
+ // be reduced by the original size of the target function, almost
+ // certainly making it negative and causing a specialization that will
+ // leave the original function dead and removable.
+ if (cost.isAlways() ||
+ (cost.isVariable() && cost.getValue() < bonus)) {
+ ValueToValueMapTy m;
+ Function::arg_iterator arg = F.arg_begin();
+ for (int y = 0; y < interestingArgs[x]; ++y)
+ ++arg;
+ m[&*arg] = ii->first;
+ SpecializeFunction(&F, m);
+ ++numSpecialized;
+ breakOuter = true;
+ Changed = true;
+ }
+ }
}
}
return Changed;
/// scanForInterest - This function decides which arguments would be worth
/// specializing on.
-void PartSpec::scanForInterest(Function& F, SmallVector<int, 6>& args) {
+void PartSpec::scanForInterest(Function& F, InterestingArgVector& args) {
for(Function::arg_iterator ii = F.arg_begin(), ee = F.arg_end();
ii != ee; ++ii) {
- for(Value::use_iterator ui = ii->use_begin(), ue = ii->use_end();
- ui != ue; ++ui) {
- // As an initial proxy for control flow, specialize on arguments
- // that are used in comparisons.
- if (isa<CmpInst>(ui)) {
- args.push_back(std::distance(F.arg_begin(), ii));
- break;
- }
+ int argno = std::distance(F.arg_begin(), ii);
+ SmallVector<unsigned, 1> argnos;
+ argnos.push_back(argno);
+ int bonus = CA.getSpecializationBonus(&F, argnos);
+ if (bonus > 0) {
+ args.push_back(argno);
}
}
}
-/// replaceUsersFor - Replace direct calls to F with NF if the arg argnum is
-/// the constant val
-void PartSpec::replaceUsersFor(Function& F , int argnum, Constant* val,
- Function* NF) {
- ++numSpecialized;
- for(Value::use_iterator ii = F.use_begin(), ee = F.use_end();
- ii != ee; ++ii)
- if (CallInst* CI = dyn_cast<CallInst>(ii))
- if (CI->getOperand(0) == &F && CI->getOperand(argnum + 1) == val)
- CI->setOperand(0, NF);
-}
-
+/// scanDistribution - Construct a histogram of constants for arg of F at arg.
+/// For each distinct constant, we'll compute the total of the specialization
+/// bonus across all callsites passing that constant; if that total exceeds
+/// the specialization cost, we will create the specialization.
int PartSpec::scanDistribution(Function& F, int arg,
std::map<Constant*, int>& dist) {
bool hasIndirect = false;
int total = 0;
- for(Value::use_iterator ii = F.use_begin(), ee = F.use_end();
- ii != ee; ++ii)
- if (CallInst* CI = dyn_cast<CallInst>(ii)) {
- ++dist[dyn_cast<Constant>(CI->getOperand(arg + 1))];
+ for (Value::use_iterator ii = F.use_begin(), ee = F.use_end();
+ ii != ee; ++ii) {
+ User *U = *ii;
+ CallSite CS(U);
+ if (CS && CS.getCalledFunction() == &F) {
+ SmallVector<unsigned, 1> argnos;
+ argnos.push_back(arg);
+ dist[dyn_cast<Constant>(CS.getArgument(arg))] +=
+ CA.getSpecializationBonus(&F, argnos);
++total;
} else
hasIndirect = true;
+ }
// Preserve the original address taken function even if all other uses
// will be specialized.