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ArgumentPromotion.cpp
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1 //===-- ArgumentPromotion.cpp - Promote by-reference arguments ------------===//
2 //
3 // The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // This pass promotes "by reference" arguments to be "by value" arguments. In
11 // practice, this means looking for internal functions that have pointer
12 // arguments. If it can prove, through the use of alias analysis, that an
13 // argument is *only* loaded, then it can pass the value into the function
14 // instead of the address of the value. This can cause recursive simplification
15 // of code and lead to the elimination of allocas (especially in C++ template
16 // code like the STL).
17 //
18 // This pass also handles aggregate arguments that are passed into a function,
19 // scalarizing them if the elements of the aggregate are only loaded. Note that
20 // by default it refuses to scalarize aggregates which would require passing in
21 // more than three operands to the function, because passing thousands of
22 // operands for a large array or structure is unprofitable! This limit can be
23 // configured or disabled, however.
24 //
25 // Note that this transformation could also be done for arguments that are only
26 // stored to (returning the value instead), but does not currently. This case
27 // would be best handled when and if LLVM begins supporting multiple return
28 // values from functions.
29 //
30 //===----------------------------------------------------------------------===//
31 
32 #define DEBUG_TYPE "argpromotion"
33 #include "llvm/Transforms/IPO.h"
35 #include "llvm/ADT/Statistic.h"
36 #include "llvm/ADT/StringExtras.h"
40 #include "llvm/IR/Constants.h"
41 #include "llvm/IR/DerivedTypes.h"
42 #include "llvm/IR/Instructions.h"
43 #include "llvm/IR/LLVMContext.h"
44 #include "llvm/IR/Module.h"
45 #include "llvm/Support/CFG.h"
46 #include "llvm/Support/CallSite.h"
47 #include "llvm/Support/Debug.h"
49 #include <set>
50 using namespace llvm;
51 
52 STATISTIC(NumArgumentsPromoted , "Number of pointer arguments promoted");
53 STATISTIC(NumAggregatesPromoted, "Number of aggregate arguments promoted");
54 STATISTIC(NumByValArgsPromoted , "Number of byval arguments promoted");
55 STATISTIC(NumArgumentsDead , "Number of dead pointer args eliminated");
56 
57 namespace {
58  /// ArgPromotion - The 'by reference' to 'by value' argument promotion pass.
59  ///
60  struct ArgPromotion : public CallGraphSCCPass {
61  virtual void getAnalysisUsage(AnalysisUsage &AU) const {
64  }
65 
66  virtual bool runOnSCC(CallGraphSCC &SCC);
67  static char ID; // Pass identification, replacement for typeid
68  explicit ArgPromotion(unsigned maxElements = 3)
69  : CallGraphSCCPass(ID), maxElements(maxElements) {
71  }
72 
73  /// A vector used to hold the indices of a single GEP instruction
74  typedef std::vector<uint64_t> IndicesVector;
75 
76  private:
77  CallGraphNode *PromoteArguments(CallGraphNode *CGN);
78  bool isSafeToPromoteArgument(Argument *Arg, bool isByVal) const;
79  CallGraphNode *DoPromotion(Function *F,
80  SmallPtrSet<Argument*, 8> &ArgsToPromote,
81  SmallPtrSet<Argument*, 8> &ByValArgsToTransform);
82  /// The maximum number of elements to expand, or 0 for unlimited.
83  unsigned maxElements;
84  };
85 }
86 
87 char ArgPromotion::ID = 0;
88 INITIALIZE_PASS_BEGIN(ArgPromotion, "argpromotion",
89  "Promote 'by reference' arguments to scalars", false, false)
93  "Promote 'by reference' arguments to scalars", false, false)
94 
95 Pass *llvm::createArgumentPromotionPass(unsigned maxElements) {
96  return new ArgPromotion(maxElements);
97 }
98 
99 bool ArgPromotion::runOnSCC(CallGraphSCC &SCC) {
100  bool Changed = false, LocalChange;
101 
102  do { // Iterate until we stop promoting from this SCC.
103  LocalChange = false;
104  // Attempt to promote arguments from all functions in this SCC.
105  for (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end(); I != E; ++I) {
106  if (CallGraphNode *CGN = PromoteArguments(*I)) {
107  LocalChange = true;
108  SCC.ReplaceNode(*I, CGN);
109  }
110  }
111  Changed |= LocalChange; // Remember that we changed something.
112  } while (LocalChange);
113 
114  return Changed;
115 }
116 
117 /// PromoteArguments - This method checks the specified function to see if there
118 /// are any promotable arguments and if it is safe to promote the function (for
119 /// example, all callers are direct). If safe to promote some arguments, it
120 /// calls the DoPromotion method.
121 ///
122 CallGraphNode *ArgPromotion::PromoteArguments(CallGraphNode *CGN) {
123  Function *F = CGN->getFunction();
124 
125  // Make sure that it is local to this module.
126  if (!F || !F->hasLocalLinkage()) return 0;
127 
128  // First check: see if there are any pointer arguments! If not, quick exit.
129  SmallVector<Argument*, 16> PointerArgs;
130  for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); I != E; ++I)
131  if (I->getType()->isPointerTy())
132  PointerArgs.push_back(I);
133  if (PointerArgs.empty()) return 0;
134 
135  // Second check: make sure that all callers are direct callers. We can't
136  // transform functions that have indirect callers. Also see if the function
137  // is self-recursive.
138  bool isSelfRecursive = false;
139  for (Value::use_iterator UI = F->use_begin(), E = F->use_end();
140  UI != E; ++UI) {
141  CallSite CS(*UI);
142  // Must be a direct call.
143  if (CS.getInstruction() == 0 || !CS.isCallee(UI)) return 0;
144 
145  if (CS.getInstruction()->getParent()->getParent() == F)
146  isSelfRecursive = true;
147  }
148 
149  // Check to see which arguments are promotable. If an argument is promotable,
150  // add it to ArgsToPromote.
151  SmallPtrSet<Argument*, 8> ArgsToPromote;
152  SmallPtrSet<Argument*, 8> ByValArgsToTransform;
153  for (unsigned i = 0, e = PointerArgs.size(); i != e; ++i) {
154  Argument *PtrArg = PointerArgs[i];
155  Type *AgTy = cast<PointerType>(PtrArg->getType())->getElementType();
156 
157  // If this is a byval argument, and if the aggregate type is small, just
158  // pass the elements, which is always safe.
159  if (PtrArg->hasByValAttr()) {
160  if (StructType *STy = dyn_cast<StructType>(AgTy)) {
161  if (maxElements > 0 && STy->getNumElements() > maxElements) {
162  DEBUG(dbgs() << "argpromotion disable promoting argument '"
163  << PtrArg->getName() << "' because it would require adding more"
164  << " than " << maxElements << " arguments to the function.\n");
165  continue;
166  }
167 
168  // If all the elements are single-value types, we can promote it.
169  bool AllSimple = true;
170  for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
171  if (!STy->getElementType(i)->isSingleValueType()) {
172  AllSimple = false;
173  break;
174  }
175  }
176 
177  // Safe to transform, don't even bother trying to "promote" it.
178  // Passing the elements as a scalar will allow scalarrepl to hack on
179  // the new alloca we introduce.
180  if (AllSimple) {
181  ByValArgsToTransform.insert(PtrArg);
182  continue;
183  }
184  }
185  }
186 
187  // If the argument is a recursive type and we're in a recursive
188  // function, we could end up infinitely peeling the function argument.
189  if (isSelfRecursive) {
190  if (StructType *STy = dyn_cast<StructType>(AgTy)) {
191  bool RecursiveType = false;
192  for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
193  if (STy->getElementType(i) == PtrArg->getType()) {
194  RecursiveType = true;
195  break;
196  }
197  }
198  if (RecursiveType)
199  continue;
200  }
201  }
202 
203  // Otherwise, see if we can promote the pointer to its value.
204  if (isSafeToPromoteArgument(PtrArg, PtrArg->hasByValAttr()))
205  ArgsToPromote.insert(PtrArg);
206  }
207 
208  // No promotable pointer arguments.
209  if (ArgsToPromote.empty() && ByValArgsToTransform.empty())
210  return 0;
211 
212  return DoPromotion(F, ArgsToPromote, ByValArgsToTransform);
213 }
214 
215 /// AllCallersPassInValidPointerForArgument - Return true if we can prove that
216 /// all callees pass in a valid pointer for the specified function argument.
218  Function *Callee = Arg->getParent();
219 
220  unsigned ArgNo = Arg->getArgNo();
221 
222  // Look at all call sites of the function. At this pointer we know we only
223  // have direct callees.
224  for (Value::use_iterator UI = Callee->use_begin(), E = Callee->use_end();
225  UI != E; ++UI) {
226  CallSite CS(*UI);
227  assert(CS && "Should only have direct calls!");
228 
229  if (!CS.getArgument(ArgNo)->isDereferenceablePointer())
230  return false;
231  }
232  return true;
233 }
234 
235 /// Returns true if Prefix is a prefix of longer. That means, Longer has a size
236 /// that is greater than or equal to the size of prefix, and each of the
237 /// elements in Prefix is the same as the corresponding elements in Longer.
238 ///
239 /// This means it also returns true when Prefix and Longer are equal!
240 static bool IsPrefix(const ArgPromotion::IndicesVector &Prefix,
241  const ArgPromotion::IndicesVector &Longer) {
242  if (Prefix.size() > Longer.size())
243  return false;
244  return std::equal(Prefix.begin(), Prefix.end(), Longer.begin());
245 }
246 
247 
248 /// Checks if Indices, or a prefix of Indices, is in Set.
249 static bool PrefixIn(const ArgPromotion::IndicesVector &Indices,
250  std::set<ArgPromotion::IndicesVector> &Set) {
251  std::set<ArgPromotion::IndicesVector>::iterator Low;
252  Low = Set.upper_bound(Indices);
253  if (Low != Set.begin())
254  Low--;
255  // Low is now the last element smaller than or equal to Indices. This means
256  // it points to a prefix of Indices (possibly Indices itself), if such
257  // prefix exists.
258  //
259  // This load is safe if any prefix of its operands is safe to load.
260  return Low != Set.end() && IsPrefix(*Low, Indices);
261 }
262 
263 /// Mark the given indices (ToMark) as safe in the given set of indices
264 /// (Safe). Marking safe usually means adding ToMark to Safe. However, if there
265 /// is already a prefix of Indices in Safe, Indices are implicitely marked safe
266 /// already. Furthermore, any indices that Indices is itself a prefix of, are
267 /// removed from Safe (since they are implicitely safe because of Indices now).
268 static void MarkIndicesSafe(const ArgPromotion::IndicesVector &ToMark,
269  std::set<ArgPromotion::IndicesVector> &Safe) {
270  std::set<ArgPromotion::IndicesVector>::iterator Low;
271  Low = Safe.upper_bound(ToMark);
272  // Guard against the case where Safe is empty
273  if (Low != Safe.begin())
274  Low--;
275  // Low is now the last element smaller than or equal to Indices. This
276  // means it points to a prefix of Indices (possibly Indices itself), if
277  // such prefix exists.
278  if (Low != Safe.end()) {
279  if (IsPrefix(*Low, ToMark))
280  // If there is already a prefix of these indices (or exactly these
281  // indices) marked a safe, don't bother adding these indices
282  return;
283 
284  // Increment Low, so we can use it as a "insert before" hint
285  ++Low;
286  }
287  // Insert
288  Low = Safe.insert(Low, ToMark);
289  ++Low;
290  // If there we're a prefix of longer index list(s), remove those
291  std::set<ArgPromotion::IndicesVector>::iterator End = Safe.end();
292  while (Low != End && IsPrefix(ToMark, *Low)) {
293  std::set<ArgPromotion::IndicesVector>::iterator Remove = Low;
294  ++Low;
295  Safe.erase(Remove);
296  }
297 }
298 
299 /// isSafeToPromoteArgument - As you might guess from the name of this method,
300 /// it checks to see if it is both safe and useful to promote the argument.
301 /// This method limits promotion of aggregates to only promote up to three
302 /// elements of the aggregate in order to avoid exploding the number of
303 /// arguments passed in.
304 bool ArgPromotion::isSafeToPromoteArgument(Argument *Arg, bool isByVal) const {
305  typedef std::set<IndicesVector> GEPIndicesSet;
306 
307  // Quick exit for unused arguments
308  if (Arg->use_empty())
309  return true;
310 
311  // We can only promote this argument if all of the uses are loads, or are GEP
312  // instructions (with constant indices) that are subsequently loaded.
313  //
314  // Promoting the argument causes it to be loaded in the caller
315  // unconditionally. This is only safe if we can prove that either the load
316  // would have happened in the callee anyway (ie, there is a load in the entry
317  // block) or the pointer passed in at every call site is guaranteed to be
318  // valid.
319  // In the former case, invalid loads can happen, but would have happened
320  // anyway, in the latter case, invalid loads won't happen. This prevents us
321  // from introducing an invalid load that wouldn't have happened in the
322  // original code.
323  //
324  // This set will contain all sets of indices that are loaded in the entry
325  // block, and thus are safe to unconditionally load in the caller.
326  GEPIndicesSet SafeToUnconditionallyLoad;
327 
328  // This set contains all the sets of indices that we are planning to promote.
329  // This makes it possible to limit the number of arguments added.
330  GEPIndicesSet ToPromote;
331 
332  // If the pointer is always valid, any load with first index 0 is valid.
333  if (isByVal || AllCallersPassInValidPointerForArgument(Arg))
334  SafeToUnconditionallyLoad.insert(IndicesVector(1, 0));
335 
336  // First, iterate the entry block and mark loads of (geps of) arguments as
337  // safe.
338  BasicBlock *EntryBlock = Arg->getParent()->begin();
339  // Declare this here so we can reuse it
340  IndicesVector Indices;
341  for (BasicBlock::iterator I = EntryBlock->begin(), E = EntryBlock->end();
342  I != E; ++I)
343  if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
344  Value *V = LI->getPointerOperand();
345  if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(V)) {
346  V = GEP->getPointerOperand();
347  if (V == Arg) {
348  // This load actually loads (part of) Arg? Check the indices then.
349  Indices.reserve(GEP->getNumIndices());
350  for (User::op_iterator II = GEP->idx_begin(), IE = GEP->idx_end();
351  II != IE; ++II)
352  if (ConstantInt *CI = dyn_cast<ConstantInt>(*II))
353  Indices.push_back(CI->getSExtValue());
354  else
355  // We found a non-constant GEP index for this argument? Bail out
356  // right away, can't promote this argument at all.
357  return false;
358 
359  // Indices checked out, mark them as safe
360  MarkIndicesSafe(Indices, SafeToUnconditionallyLoad);
361  Indices.clear();
362  }
363  } else if (V == Arg) {
364  // Direct loads are equivalent to a GEP with a single 0 index.
365  MarkIndicesSafe(IndicesVector(1, 0), SafeToUnconditionallyLoad);
366  }
367  }
368 
369  // Now, iterate all uses of the argument to see if there are any uses that are
370  // not (GEP+)loads, or any (GEP+)loads that are not safe to promote.
372  IndicesVector Operands;
373  for (Value::use_iterator UI = Arg->use_begin(), E = Arg->use_end();
374  UI != E; ++UI) {
375  User *U = *UI;
376  Operands.clear();
377  if (LoadInst *LI = dyn_cast<LoadInst>(U)) {
378  // Don't hack volatile/atomic loads
379  if (!LI->isSimple()) return false;
380  Loads.push_back(LI);
381  // Direct loads are equivalent to a GEP with a zero index and then a load.
382  Operands.push_back(0);
383  } else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(U)) {
384  if (GEP->use_empty()) {
385  // Dead GEP's cause trouble later. Just remove them if we run into
386  // them.
387  getAnalysis<AliasAnalysis>().deleteValue(GEP);
388  GEP->eraseFromParent();
389  // TODO: This runs the above loop over and over again for dead GEPs
390  // Couldn't we just do increment the UI iterator earlier and erase the
391  // use?
392  return isSafeToPromoteArgument(Arg, isByVal);
393  }
394 
395  // Ensure that all of the indices are constants.
396  for (User::op_iterator i = GEP->idx_begin(), e = GEP->idx_end();
397  i != e; ++i)
398  if (ConstantInt *C = dyn_cast<ConstantInt>(*i))
399  Operands.push_back(C->getSExtValue());
400  else
401  return false; // Not a constant operand GEP!
402 
403  // Ensure that the only users of the GEP are load instructions.
404  for (Value::use_iterator UI = GEP->use_begin(), E = GEP->use_end();
405  UI != E; ++UI)
406  if (LoadInst *LI = dyn_cast<LoadInst>(*UI)) {
407  // Don't hack volatile/atomic loads
408  if (!LI->isSimple()) return false;
409  Loads.push_back(LI);
410  } else {
411  // Other uses than load?
412  return false;
413  }
414  } else {
415  return false; // Not a load or a GEP.
416  }
417 
418  // Now, see if it is safe to promote this load / loads of this GEP. Loading
419  // is safe if Operands, or a prefix of Operands, is marked as safe.
420  if (!PrefixIn(Operands, SafeToUnconditionallyLoad))
421  return false;
422 
423  // See if we are already promoting a load with these indices. If not, check
424  // to make sure that we aren't promoting too many elements. If so, nothing
425  // to do.
426  if (ToPromote.find(Operands) == ToPromote.end()) {
427  if (maxElements > 0 && ToPromote.size() == maxElements) {
428  DEBUG(dbgs() << "argpromotion not promoting argument '"
429  << Arg->getName() << "' because it would require adding more "
430  << "than " << maxElements << " arguments to the function.\n");
431  // We limit aggregate promotion to only promoting up to a fixed number
432  // of elements of the aggregate.
433  return false;
434  }
435  ToPromote.insert(Operands);
436  }
437  }
438 
439  if (Loads.empty()) return true; // No users, this is a dead argument.
440 
441  // Okay, now we know that the argument is only used by load instructions and
442  // it is safe to unconditionally perform all of them. Use alias analysis to
443  // check to see if the pointer is guaranteed to not be modified from entry of
444  // the function to each of the load instructions.
445 
446  // Because there could be several/many load instructions, remember which
447  // blocks we know to be transparent to the load.
448  SmallPtrSet<BasicBlock*, 16> TranspBlocks;
449 
450  AliasAnalysis &AA = getAnalysis<AliasAnalysis>();
451 
452  for (unsigned i = 0, e = Loads.size(); i != e; ++i) {
453  // Check to see if the load is invalidated from the start of the block to
454  // the load itself.
455  LoadInst *Load = Loads[i];
456  BasicBlock *BB = Load->getParent();
457 
458  AliasAnalysis::Location Loc = AA.getLocation(Load);
459  if (AA.canInstructionRangeModify(BB->front(), *Load, Loc))
460  return false; // Pointer is invalidated!
461 
462  // Now check every path from the entry block to the load for transparency.
463  // To do this, we perform a depth first search on the inverse CFG from the
464  // loading block.
465  for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
466  BasicBlock *P = *PI;
468  I = idf_ext_begin(P, TranspBlocks),
469  E = idf_ext_end(P, TranspBlocks); I != E; ++I)
470  if (AA.canBasicBlockModify(**I, Loc))
471  return false;
472  }
473  }
474 
475  // If the path from the entry of the function to each load is free of
476  // instructions that potentially invalidate the load, we can make the
477  // transformation!
478  return true;
479 }
480 
481 /// DoPromotion - This method actually performs the promotion of the specified
482 /// arguments, and returns the new function. At this point, we know that it's
483 /// safe to do so.
484 CallGraphNode *ArgPromotion::DoPromotion(Function *F,
485  SmallPtrSet<Argument*, 8> &ArgsToPromote,
486  SmallPtrSet<Argument*, 8> &ByValArgsToTransform) {
487 
488  // Start by computing a new prototype for the function, which is the same as
489  // the old function, but has modified arguments.
490  FunctionType *FTy = F->getFunctionType();
491  std::vector<Type*> Params;
492 
493  typedef std::set<IndicesVector> ScalarizeTable;
494 
495  // ScalarizedElements - If we are promoting a pointer that has elements
496  // accessed out of it, keep track of which elements are accessed so that we
497  // can add one argument for each.
498  //
499  // Arguments that are directly loaded will have a zero element value here, to
500  // handle cases where there are both a direct load and GEP accesses.
501  //
502  std::map<Argument*, ScalarizeTable> ScalarizedElements;
503 
504  // OriginalLoads - Keep track of a representative load instruction from the
505  // original function so that we can tell the alias analysis implementation
506  // what the new GEP/Load instructions we are inserting look like.
507  // We need to keep the original loads for each argument and the elements
508  // of the argument that are accessed.
509  std::map<std::pair<Argument*, IndicesVector>, LoadInst*> OriginalLoads;
510 
511  // Attribute - Keep track of the parameter attributes for the arguments
512  // that we are *not* promoting. For the ones that we do promote, the parameter
513  // attributes are lost
514  SmallVector<AttributeSet, 8> AttributesVec;
515  const AttributeSet &PAL = F->getAttributes();
516 
517  // Add any return attributes.
518  if (PAL.hasAttributes(AttributeSet::ReturnIndex))
519  AttributesVec.push_back(AttributeSet::get(F->getContext(),
520  PAL.getRetAttributes()));
521 
522  // First, determine the new argument list
523  unsigned ArgIndex = 1;
524  for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); I != E;
525  ++I, ++ArgIndex) {
526  if (ByValArgsToTransform.count(I)) {
527  // Simple byval argument? Just add all the struct element types.
528  Type *AgTy = cast<PointerType>(I->getType())->getElementType();
529  StructType *STy = cast<StructType>(AgTy);
530  for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i)
531  Params.push_back(STy->getElementType(i));
532  ++NumByValArgsPromoted;
533  } else if (!ArgsToPromote.count(I)) {
534  // Unchanged argument
535  Params.push_back(I->getType());
536  AttributeSet attrs = PAL.getParamAttributes(ArgIndex);
537  if (attrs.hasAttributes(ArgIndex)) {
538  AttrBuilder B(attrs, ArgIndex);
539  AttributesVec.
540  push_back(AttributeSet::get(F->getContext(), Params.size(), B));
541  }
542  } else if (I->use_empty()) {
543  // Dead argument (which are always marked as promotable)
544  ++NumArgumentsDead;
545  } else {
546  // Okay, this is being promoted. This means that the only uses are loads
547  // or GEPs which are only used by loads
548 
549  // In this table, we will track which indices are loaded from the argument
550  // (where direct loads are tracked as no indices).
551  ScalarizeTable &ArgIndices = ScalarizedElements[I];
552  for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); UI != E;
553  ++UI) {
554  Instruction *User = cast<Instruction>(*UI);
555  assert(isa<LoadInst>(User) || isa<GetElementPtrInst>(User));
556  IndicesVector Indices;
557  Indices.reserve(User->getNumOperands() - 1);
558  // Since loads will only have a single operand, and GEPs only a single
559  // non-index operand, this will record direct loads without any indices,
560  // and gep+loads with the GEP indices.
561  for (User::op_iterator II = User->op_begin() + 1, IE = User->op_end();
562  II != IE; ++II)
563  Indices.push_back(cast<ConstantInt>(*II)->getSExtValue());
564  // GEPs with a single 0 index can be merged with direct loads
565  if (Indices.size() == 1 && Indices.front() == 0)
566  Indices.clear();
567  ArgIndices.insert(Indices);
568  LoadInst *OrigLoad;
569  if (LoadInst *L = dyn_cast<LoadInst>(User))
570  OrigLoad = L;
571  else
572  // Take any load, we will use it only to update Alias Analysis
573  OrigLoad = cast<LoadInst>(User->use_back());
574  OriginalLoads[std::make_pair(I, Indices)] = OrigLoad;
575  }
576 
577  // Add a parameter to the function for each element passed in.
578  for (ScalarizeTable::iterator SI = ArgIndices.begin(),
579  E = ArgIndices.end(); SI != E; ++SI) {
580  // not allowed to dereference ->begin() if size() is 0
581  Params.push_back(GetElementPtrInst::getIndexedType(I->getType(), *SI));
582  assert(Params.back());
583  }
584 
585  if (ArgIndices.size() == 1 && ArgIndices.begin()->empty())
586  ++NumArgumentsPromoted;
587  else
588  ++NumAggregatesPromoted;
589  }
590  }
591 
592  // Add any function attributes.
593  if (PAL.hasAttributes(AttributeSet::FunctionIndex))
594  AttributesVec.push_back(AttributeSet::get(FTy->getContext(),
595  PAL.getFnAttributes()));
596 
597  Type *RetTy = FTy->getReturnType();
598 
599  // Construct the new function type using the new arguments.
600  FunctionType *NFTy = FunctionType::get(RetTy, Params, FTy->isVarArg());
601 
602  // Create the new function body and insert it into the module.
603  Function *NF = Function::Create(NFTy, F->getLinkage(), F->getName());
604  NF->copyAttributesFrom(F);
605 
606 
607  DEBUG(dbgs() << "ARG PROMOTION: Promoting to:" << *NF << "\n"
608  << "From: " << *F);
609 
610  // Recompute the parameter attributes list based on the new arguments for
611  // the function.
612  NF->setAttributes(AttributeSet::get(F->getContext(), AttributesVec));
613  AttributesVec.clear();
614 
615  F->getParent()->getFunctionList().insert(F, NF);
616  NF->takeName(F);
617 
618  // Get the alias analysis information that we need to update to reflect our
619  // changes.
620  AliasAnalysis &AA = getAnalysis<AliasAnalysis>();
621 
622  // Get the callgraph information that we need to update to reflect our
623  // changes.
624  CallGraph &CG = getAnalysis<CallGraph>();
625 
626  // Get a new callgraph node for NF.
627  CallGraphNode *NF_CGN = CG.getOrInsertFunction(NF);
628 
629  // Loop over all of the callers of the function, transforming the call sites
630  // to pass in the loaded pointers.
631  //
633  while (!F->use_empty()) {
634  CallSite CS(F->use_back());
635  assert(CS.getCalledFunction() == F);
636  Instruction *Call = CS.getInstruction();
637  const AttributeSet &CallPAL = CS.getAttributes();
638 
639  // Add any return attributes.
640  if (CallPAL.hasAttributes(AttributeSet::ReturnIndex))
641  AttributesVec.push_back(AttributeSet::get(F->getContext(),
642  CallPAL.getRetAttributes()));
643 
644  // Loop over the operands, inserting GEP and loads in the caller as
645  // appropriate.
646  CallSite::arg_iterator AI = CS.arg_begin();
647  ArgIndex = 1;
648  for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end();
649  I != E; ++I, ++AI, ++ArgIndex)
650  if (!ArgsToPromote.count(I) && !ByValArgsToTransform.count(I)) {
651  Args.push_back(*AI); // Unmodified argument
652 
653  if (CallPAL.hasAttributes(ArgIndex)) {
654  AttrBuilder B(CallPAL, ArgIndex);
655  AttributesVec.
656  push_back(AttributeSet::get(F->getContext(), Args.size(), B));
657  }
658  } else if (ByValArgsToTransform.count(I)) {
659  // Emit a GEP and load for each element of the struct.
660  Type *AgTy = cast<PointerType>(I->getType())->getElementType();
661  StructType *STy = cast<StructType>(AgTy);
662  Value *Idxs[2] = {
664  for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
665  Idxs[1] = ConstantInt::get(Type::getInt32Ty(F->getContext()), i);
666  Value *Idx = GetElementPtrInst::Create(*AI, Idxs,
667  (*AI)->getName()+"."+utostr(i),
668  Call);
669  // TODO: Tell AA about the new values?
670  Args.push_back(new LoadInst(Idx, Idx->getName()+".val", Call));
671  }
672  } else if (!I->use_empty()) {
673  // Non-dead argument: insert GEPs and loads as appropriate.
674  ScalarizeTable &ArgIndices = ScalarizedElements[I];
675  // Store the Value* version of the indices in here, but declare it now
676  // for reuse.
677  std::vector<Value*> Ops;
678  for (ScalarizeTable::iterator SI = ArgIndices.begin(),
679  E = ArgIndices.end(); SI != E; ++SI) {
680  Value *V = *AI;
681  LoadInst *OrigLoad = OriginalLoads[std::make_pair(I, *SI)];
682  if (!SI->empty()) {
683  Ops.reserve(SI->size());
684  Type *ElTy = V->getType();
685  for (IndicesVector::const_iterator II = SI->begin(),
686  IE = SI->end(); II != IE; ++II) {
687  // Use i32 to index structs, and i64 for others (pointers/arrays).
688  // This satisfies GEP constraints.
689  Type *IdxTy = (ElTy->isStructTy() ?
692  Ops.push_back(ConstantInt::get(IdxTy, *II));
693  // Keep track of the type we're currently indexing.
694  ElTy = cast<CompositeType>(ElTy)->getTypeAtIndex(*II);
695  }
696  // And create a GEP to extract those indices.
697  V = GetElementPtrInst::Create(V, Ops, V->getName()+".idx", Call);
698  Ops.clear();
699  AA.copyValue(OrigLoad->getOperand(0), V);
700  }
701  // Since we're replacing a load make sure we take the alignment
702  // of the previous load.
703  LoadInst *newLoad = new LoadInst(V, V->getName()+".val", Call);
704  newLoad->setAlignment(OrigLoad->getAlignment());
705  // Transfer the TBAA info too.
707  OrigLoad->getMetadata(LLVMContext::MD_tbaa));
708  Args.push_back(newLoad);
709  AA.copyValue(OrigLoad, Args.back());
710  }
711  }
712 
713  // Push any varargs arguments on the list.
714  for (; AI != CS.arg_end(); ++AI, ++ArgIndex) {
715  Args.push_back(*AI);
716  if (CallPAL.hasAttributes(ArgIndex)) {
717  AttrBuilder B(CallPAL, ArgIndex);
718  AttributesVec.
719  push_back(AttributeSet::get(F->getContext(), Args.size(), B));
720  }
721  }
722 
723  // Add any function attributes.
724  if (CallPAL.hasAttributes(AttributeSet::FunctionIndex))
725  AttributesVec.push_back(AttributeSet::get(Call->getContext(),
726  CallPAL.getFnAttributes()));
727 
728  Instruction *New;
729  if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) {
730  New = InvokeInst::Create(NF, II->getNormalDest(), II->getUnwindDest(),
731  Args, "", Call);
732  cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv());
733  cast<InvokeInst>(New)->setAttributes(AttributeSet::get(II->getContext(),
734  AttributesVec));
735  } else {
736  New = CallInst::Create(NF, Args, "", Call);
737  cast<CallInst>(New)->setCallingConv(CS.getCallingConv());
738  cast<CallInst>(New)->setAttributes(AttributeSet::get(New->getContext(),
739  AttributesVec));
740  if (cast<CallInst>(Call)->isTailCall())
741  cast<CallInst>(New)->setTailCall();
742  }
743  Args.clear();
744  AttributesVec.clear();
745 
746  // Update the alias analysis implementation to know that we are replacing
747  // the old call with a new one.
748  AA.replaceWithNewValue(Call, New);
749 
750  // Update the callgraph to know that the callsite has been transformed.
751  CallGraphNode *CalleeNode = CG[Call->getParent()->getParent()];
752  CalleeNode->replaceCallEdge(Call, New, NF_CGN);
753 
754  if (!Call->use_empty()) {
755  Call->replaceAllUsesWith(New);
756  New->takeName(Call);
757  }
758 
759  // Finally, remove the old call from the program, reducing the use-count of
760  // F.
761  Call->eraseFromParent();
762  }
763 
764  // Since we have now created the new function, splice the body of the old
765  // function right into the new function, leaving the old rotting hulk of the
766  // function empty.
767  NF->getBasicBlockList().splice(NF->begin(), F->getBasicBlockList());
768 
769  // Loop over the argument list, transferring uses of the old arguments over to
770  // the new arguments, also transferring over the names as well.
771  //
772  for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(),
773  I2 = NF->arg_begin(); I != E; ++I) {
774  if (!ArgsToPromote.count(I) && !ByValArgsToTransform.count(I)) {
775  // If this is an unmodified argument, move the name and users over to the
776  // new version.
777  I->replaceAllUsesWith(I2);
778  I2->takeName(I);
779  AA.replaceWithNewValue(I, I2);
780  ++I2;
781  continue;
782  }
783 
784  if (ByValArgsToTransform.count(I)) {
785  // In the callee, we create an alloca, and store each of the new incoming
786  // arguments into the alloca.
787  Instruction *InsertPt = NF->begin()->begin();
788 
789  // Just add all the struct element types.
790  Type *AgTy = cast<PointerType>(I->getType())->getElementType();
791  Value *TheAlloca = new AllocaInst(AgTy, 0, "", InsertPt);
792  StructType *STy = cast<StructType>(AgTy);
793  Value *Idxs[2] = {
795 
796  for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
797  Idxs[1] = ConstantInt::get(Type::getInt32Ty(F->getContext()), i);
798  Value *Idx =
799  GetElementPtrInst::Create(TheAlloca, Idxs,
800  TheAlloca->getName()+"."+Twine(i),
801  InsertPt);
802  I2->setName(I->getName()+"."+Twine(i));
803  new StoreInst(I2++, Idx, InsertPt);
804  }
805 
806  // Anything that used the arg should now use the alloca.
807  I->replaceAllUsesWith(TheAlloca);
808  TheAlloca->takeName(I);
809  AA.replaceWithNewValue(I, TheAlloca);
810  continue;
811  }
812 
813  if (I->use_empty()) {
814  AA.deleteValue(I);
815  continue;
816  }
817 
818  // Otherwise, if we promoted this argument, then all users are load
819  // instructions (or GEPs with only load users), and all loads should be
820  // using the new argument that we added.
821  ScalarizeTable &ArgIndices = ScalarizedElements[I];
822 
823  while (!I->use_empty()) {
824  if (LoadInst *LI = dyn_cast<LoadInst>(I->use_back())) {
825  assert(ArgIndices.begin()->empty() &&
826  "Load element should sort to front!");
827  I2->setName(I->getName()+".val");
828  LI->replaceAllUsesWith(I2);
829  AA.replaceWithNewValue(LI, I2);
830  LI->eraseFromParent();
831  DEBUG(dbgs() << "*** Promoted load of argument '" << I->getName()
832  << "' in function '" << F->getName() << "'\n");
833  } else {
834  GetElementPtrInst *GEP = cast<GetElementPtrInst>(I->use_back());
835  IndicesVector Operands;
836  Operands.reserve(GEP->getNumIndices());
837  for (User::op_iterator II = GEP->idx_begin(), IE = GEP->idx_end();
838  II != IE; ++II)
839  Operands.push_back(cast<ConstantInt>(*II)->getSExtValue());
840 
841  // GEPs with a single 0 index can be merged with direct loads
842  if (Operands.size() == 1 && Operands.front() == 0)
843  Operands.clear();
844 
845  Function::arg_iterator TheArg = I2;
846  for (ScalarizeTable::iterator It = ArgIndices.begin();
847  *It != Operands; ++It, ++TheArg) {
848  assert(It != ArgIndices.end() && "GEP not handled??");
849  }
850 
851  std::string NewName = I->getName();
852  for (unsigned i = 0, e = Operands.size(); i != e; ++i) {
853  NewName += "." + utostr(Operands[i]);
854  }
855  NewName += ".val";
856  TheArg->setName(NewName);
857 
858  DEBUG(dbgs() << "*** Promoted agg argument '" << TheArg->getName()
859  << "' of function '" << NF->getName() << "'\n");
860 
861  // All of the uses must be load instructions. Replace them all with
862  // the argument specified by ArgNo.
863  while (!GEP->use_empty()) {
864  LoadInst *L = cast<LoadInst>(GEP->use_back());
865  L->replaceAllUsesWith(TheArg);
866  AA.replaceWithNewValue(L, TheArg);
867  L->eraseFromParent();
868  }
869  AA.deleteValue(GEP);
870  GEP->eraseFromParent();
871  }
872  }
873 
874  // Increment I2 past all of the arguments added for this promoted pointer.
875  std::advance(I2, ArgIndices.size());
876  }
877 
878  // Tell the alias analysis that the old function is about to disappear.
879  AA.replaceWithNewValue(F, NF);
880 
881 
882  NF_CGN->stealCalledFunctionsFrom(CG[F]);
883 
884  // Now that the old function is dead, delete it. If there is a dangling
885  // reference to the CallgraphNode, just leave the dead function around for
886  // someone else to nuke.
887  CallGraphNode *CGN = CG[F];
888  if (CGN->getNumReferences() == 0)
889  delete CG.removeFunctionFromModule(CGN);
890  else
891  F->setLinkage(Function::ExternalLinkage);
892 
893  return NF_CGN;
894 }
void replaceWithNewValue(Value *Old, Value *New)
use_iterator use_end()
Definition: Value.h:152
LinkageTypes getLinkage() const
Definition: GlobalValue.h:218
static PassRegistry * getPassRegistry()
LLVMContext & getContext() const
Definition: Function.cpp:167
LLVM Argument representation.
Definition: Argument.h:35
AttributeSet getParamAttributes(unsigned Index) const
The attributes for the specified index are returned.
Definition: Attributes.cpp:792
std::vector< CallGraphNode * >::const_iterator iterator
unsigned getNumOperands() const
Definition: User.h:108
bool insert(PtrType Ptr)
Definition: SmallPtrSet.h:253
Externally visible function.
Definition: GlobalValue.h:34
bool canBasicBlockModify(const BasicBlock &BB, const Location &Loc)
arg_iterator arg_end()
Definition: Function.h:418
const Instruction & front() const
Definition: BasicBlock.h:205
F(f)
static IntegerType * getInt64Ty(LLVMContext &C)
Definition: Type.cpp:242
unsigned getNumIndices() const
Definition: Instructions.h:827
op_iterator op_begin()
Definition: User.h:116
virtual void getAnalysisUsage(AnalysisUsage &Info) const
LoopInfoBase< BlockT, LoopT > * LI
Definition: LoopInfoImpl.h:411
ValTy * getArgument(unsigned ArgNo) const
Definition: CallSite.h:111
AttributeSet getRetAttributes() const
The attributes for the ret value are returned.
Definition: Attributes.cpp:800
StringRef getName() const
Definition: Value.cpp:167
Function * getFunction() const
Definition: CallGraph.h:212
iterator begin()
Definition: BasicBlock.h:193
unsigned getNumReferences() const
Definition: CallGraph.h:223
INITIALIZE_PASS_BEGIN(ArgPromotion,"argpromotion","Promote 'by reference' arguments to scalars", false, false) INITIALIZE_PASS_END(ArgPromotion
AnalysisUsage & addRequired()
#define INITIALIZE_PASS_DEPENDENCY(depName)
Definition: PassSupport.h:167
static error_code advance(T &it, size_t Val)
Promote by reference arguments to scalars
iterator end() const
void replaceCallEdge(CallSite CS, CallSite NewCS, CallGraphNode *NewNode)
Definition: CallGraph.cpp:249
Definition: Use.h:60
void initializeArgPromotionPass(PassRegistry &)
#define INITIALIZE_PASS_END(passName, arg, name, cfg, analysis)
Definition: PassSupport.h:172
Pass * createArgumentPromotionPass(unsigned maxElements=3)
void setName(const Twine &Name)
Definition: Value.cpp:175
void copyAttributesFrom(const GlobalValue *Src)
Definition: Function.cpp:347
ID
LLVM Calling Convention Representation.
Definition: CallingConv.h:26
virtual void copyValue(Value *From, Value *To)
LLVMContext & getContext() const
getContext - Return the LLVMContext in which this type was uniqued.
Definition: Type.h:128
bool count(PtrType Ptr) const
count - Return true if the specified pointer is in the set.
Definition: SmallPtrSet.h:264
bool LLVM_ATTRIBUTE_UNUSED_RESULT empty() const
Definition: SmallVector.h:56
op_iterator idx_begin()
Definition: Instructions.h:785
static FunctionType * get(Type *Result, ArrayRef< Type * > Params, bool isVarArg)
Definition: Type.cpp:361
static std::string utostr(uint64_t X, bool isNeg=false)
Definition: StringExtras.h:88
void replaceAllUsesWith(Value *V)
Definition: Value.cpp:303
void takeName(Value *V)
Definition: Value.cpp:239
iterator begin()
Definition: Function.h:395
#define P(N)
static bool IsPrefix(const ArgPromotion::IndicesVector &Prefix, const ArgPromotion::IndicesVector &Longer)
LLVM Basic Block Representation.
Definition: BasicBlock.h:72
const Function * getParent() const
Definition: Argument.h:49
Type * getElementType(unsigned N) const
Definition: DerivedTypes.h:287
idf_ext_iterator< T, SetTy > idf_ext_end(const T &G, SetTy &S)
static InvokeInst * Create(Value *Func, BasicBlock *IfNormal, BasicBlock *IfException, ArrayRef< Value * > Args, const Twine &NameStr="", Instruction *InsertBefore=0)
Interval::pred_iterator pred_begin(Interval *I)
Definition: Interval.h:117
op_iterator op_end()
Definition: User.h:118
iterator insert(iterator where, NodeTy *New)
Definition: ilist.h:412
Value * getOperand(unsigned i) const
Definition: User.h:88
Interval::pred_iterator pred_end(Interval *I)
Definition: Interval.h:120
arg_iterator arg_begin()
Definition: Function.h:410
Location - A description of a memory location.
bool LLVM_ATTRIBUTE_UNUSED_RESULT empty() const
Definition: SmallPtrSet.h:74
void setAlignment(unsigned Align)
#define INITIALIZE_AG_DEPENDENCY(depName)
Definition: PassSupport.h:169
virtual void deleteValue(Value *V)
LLVMContext & getContext() const
All values hold a context through their type.
Definition: Value.cpp:517
void setMetadata(unsigned KindID, MDNode *Node)
Definition: Metadata.cpp:589
idf_ext_iterator< T, SetTy > idf_ext_begin(const T &G, SetTy &S)
static CallInst * Create(Value *Func, ArrayRef< Value * > Args, const Twine &NameStr="", Instruction *InsertBefore=0)
bool hasByValAttr() const
Return true if this argument has the byval attribute on it in its containing function.
Definition: Function.cpp:81
const FunctionListType & getFunctionList() const
Get the Module's list of functions (constant).
Definition: Module.h:492
const BasicBlockListType & getBasicBlockList() const
Definition: Function.h:374
Class for constant integers.
Definition: Constants.h:51
iterator end()
Definition: BasicBlock.h:195
Type * getType() const
Definition: Value.h:111
MDNode * getMetadata(unsigned KindID) const
Definition: Instruction.h:140
STATISTIC(NumArgumentsPromoted,"Number of pointer arguments promoted")
static Constant * get(Type *Ty, uint64_t V, bool isSigned=false)
Definition: Constants.cpp:492
static GetElementPtrInst * Create(Value *Ptr, ArrayRef< Value * > IdxList, const Twine &NameStr="", Instruction *InsertBefore=0)
Definition: Instructions.h:726
raw_ostream & dbgs()
dbgs - Return a circular-buffered debug stream.
Definition: Debug.cpp:101
AttributeSet getAttributes() const
Return the attribute list for this Function.
Definition: Function.h:170
iterator begin() const
Instruction * use_back()
Definition: Instruction.h:49
Location getLocation(const LoadInst *LI)
argpromotion
bool isStructTy() const
Definition: Type.h:212
static bool PrefixIn(const ArgPromotion::IndicesVector &Indices, std::set< ArgPromotion::IndicesVector > &Set)
Checks if Indices, or a prefix of Indices, is in Set.
bool isDereferenceablePointer() const
Definition: Value.cpp:500
use_iterator use_begin()
Definition: Value.h:150
static void MarkIndicesSafe(const ArgPromotion::IndicesVector &ToMark, std::set< ArgPromotion::IndicesVector > &Safe)
void ReplaceNode(CallGraphNode *Old, CallGraphNode *New)
static IntegerType * getInt32Ty(LLVMContext &C)
Definition: Type.cpp:241
User * use_back()
Definition: Value.h:154
bool hasAttributes(unsigned Index) const
Return true if attribute exists at the given index.
Definition: Attributes.cpp:828
unsigned getAlignment() const
Definition: Instructions.h:181
#define I(x, y, z)
Definition: MD5.cpp:54
FunctionType * getFunctionType() const
Definition: Function.cpp:171
bool hasLocalLinkage() const
Definition: GlobalValue.h:211
bool isVarArg() const
Definition: DerivedTypes.h:120
bool use_empty() const
Definition: Value.h:149
Type * getReturnType() const
Definition: DerivedTypes.h:121
static Type * getIndexedType(Type *Ptr, ArrayRef< Value * > IdxList)
static bool AllCallersPassInValidPointerForArgument(Argument *Arg)
Module * getParent()
Definition: GlobalValue.h:286
LLVM Value Representation.
Definition: Value.h:66
CallGraphSCC - This is a single SCC that a CallGraphSCCPass is run on.
bool canInstructionRangeModify(const Instruction &I1, const Instruction &I2, const Location &Loc)
unsigned getArgNo() const
Return the index of this formal argument in its containing function.
Definition: Function.cpp:67
#define DEBUG(X)
Definition: Debug.h:97
Promote by reference arguments to false
unsigned getNumElements() const
Random access to the elements.
Definition: DerivedTypes.h:286
const BasicBlock * getParent() const
Definition: Instruction.h:52
static Function * Create(FunctionType *Ty, LinkageTypes Linkage, const Twine &N="", Module *M=0)
Definition: Function.h:128
AttributeSet getFnAttributes() const
The function attributes are returned.
Definition: Attributes.cpp:809