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#include "llvm/Transforms/IPO.h"
33#include "llvm/ADT/DepthFirstIterator.h"
34#include "llvm/ADT/Statistic.h"
35#include "llvm/ADT/StringExtras.h"
36#include "llvm/Analysis/AliasAnalysis.h"
37#include "llvm/Analysis/CallGraph.h"
38#include "llvm/Analysis/CallGraphSCCPass.h"
39#include "llvm/IR/CFG.h"
40#include "llvm/IR/CallSite.h"
41#include "llvm/IR/Constants.h"
42#include "llvm/IR/DataLayout.h"
43#include "llvm/IR/DebugInfo.h"
44#include "llvm/IR/DerivedTypes.h"
45#include "llvm/IR/Instructions.h"
46#include "llvm/IR/LLVMContext.h"
47#include "llvm/IR/Module.h"
48#include "llvm/Support/Debug.h"
49#include "llvm/Support/raw_ostream.h"
50#include <set>
51using namespace llvm;
52
53#define DEBUG_TYPE "argpromotion"
54
55STATISTIC(NumArgumentsPromoted , "Number of pointer arguments promoted");
56STATISTIC(NumAggregatesPromoted, "Number of aggregate arguments promoted");
57STATISTIC(NumByValArgsPromoted , "Number of byval arguments promoted");
58STATISTIC(NumArgumentsDead     , "Number of dead pointer args eliminated");
59
60namespace {
61  /// ArgPromotion - The 'by reference' to 'by value' argument promotion pass.
62  ///
63  struct ArgPromotion : public CallGraphSCCPass {
64    void getAnalysisUsage(AnalysisUsage &AU) const override {
65      AU.addRequired<AliasAnalysis>();
66      CallGraphSCCPass::getAnalysisUsage(AU);
67    }
68
69    bool runOnSCC(CallGraphSCC &SCC) override;
70    static char ID; // Pass identification, replacement for typeid
71    explicit ArgPromotion(unsigned maxElements = 3)
72        : CallGraphSCCPass(ID), DL(nullptr), maxElements(maxElements) {
73      initializeArgPromotionPass(*PassRegistry::getPassRegistry());
74    }
75
76    /// A vector used to hold the indices of a single GEP instruction
77    typedef std::vector<uint64_t> IndicesVector;
78
79    const DataLayout *DL;
80  private:
81    CallGraphNode *PromoteArguments(CallGraphNode *CGN);
82    bool isSafeToPromoteArgument(Argument *Arg, bool isByVal) const;
83    CallGraphNode *DoPromotion(Function *F,
84                               SmallPtrSet<Argument*, 8> &ArgsToPromote,
85                               SmallPtrSet<Argument*, 8> &ByValArgsToTransform);
86    bool doInitialization(CallGraph &CG) override;
87    /// The maximum number of elements to expand, or 0 for unlimited.
88    unsigned maxElements;
89    DenseMap<const Function *, DISubprogram> FunctionDIs;
90  };
91}
92
93char ArgPromotion::ID = 0;
94INITIALIZE_PASS_BEGIN(ArgPromotion, "argpromotion",
95                "Promote 'by reference' arguments to scalars", false, false)
96INITIALIZE_AG_DEPENDENCY(AliasAnalysis)
97INITIALIZE_PASS_DEPENDENCY(CallGraphWrapperPass)
98INITIALIZE_PASS_END(ArgPromotion, "argpromotion",
99                "Promote 'by reference' arguments to scalars", false, false)
100
101Pass *llvm::createArgumentPromotionPass(unsigned maxElements) {
102  return new ArgPromotion(maxElements);
103}
104
105bool ArgPromotion::runOnSCC(CallGraphSCC &SCC) {
106  bool Changed = false, LocalChange;
107
108  DataLayoutPass *DLP = getAnalysisIfAvailable<DataLayoutPass>();
109  DL = DLP ? &DLP->getDataLayout() : nullptr;
110
111  do {  // Iterate until we stop promoting from this SCC.
112    LocalChange = false;
113    // Attempt to promote arguments from all functions in this SCC.
114    for (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end(); I != E; ++I) {
115      if (CallGraphNode *CGN = PromoteArguments(*I)) {
116        LocalChange = true;
117        SCC.ReplaceNode(*I, CGN);
118      }
119    }
120    Changed |= LocalChange;               // Remember that we changed something.
121  } while (LocalChange);
122
123  return Changed;
124}
125
126/// PromoteArguments - This method checks the specified function to see if there
127/// are any promotable arguments and if it is safe to promote the function (for
128/// example, all callers are direct).  If safe to promote some arguments, it
129/// calls the DoPromotion method.
130///
131CallGraphNode *ArgPromotion::PromoteArguments(CallGraphNode *CGN) {
132  Function *F = CGN->getFunction();
133
134  // Make sure that it is local to this module.
135  if (!F || !F->hasLocalLinkage()) return nullptr;
136
137  // First check: see if there are any pointer arguments!  If not, quick exit.
138  SmallVector<Argument*, 16> PointerArgs;
139  for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); I != E; ++I)
140    if (I->getType()->isPointerTy())
141      PointerArgs.push_back(I);
142  if (PointerArgs.empty()) return nullptr;
143
144  // Second check: make sure that all callers are direct callers.  We can't
145  // transform functions that have indirect callers.  Also see if the function
146  // is self-recursive.
147  bool isSelfRecursive = false;
148  for (Use &U : F->uses()) {
149    CallSite CS(U.getUser());
150    // Must be a direct call.
151    if (CS.getInstruction() == nullptr || !CS.isCallee(&U)) return nullptr;
152
153    if (CS.getInstruction()->getParent()->getParent() == F)
154      isSelfRecursive = true;
155  }
156
157  // Check to see which arguments are promotable.  If an argument is promotable,
158  // add it to ArgsToPromote.
159  SmallPtrSet<Argument*, 8> ArgsToPromote;
160  SmallPtrSet<Argument*, 8> ByValArgsToTransform;
161  for (unsigned i = 0, e = PointerArgs.size(); i != e; ++i) {
162    Argument *PtrArg = PointerArgs[i];
163    Type *AgTy = cast<PointerType>(PtrArg->getType())->getElementType();
164
165    // If this is a byval argument, and if the aggregate type is small, just
166    // pass the elements, which is always safe.  This does not apply to
167    // inalloca.
168    if (PtrArg->hasByValAttr()) {
169      if (StructType *STy = dyn_cast<StructType>(AgTy)) {
170        if (maxElements > 0 && STy->getNumElements() > maxElements) {
171          DEBUG(dbgs() << "argpromotion disable promoting argument '"
172                << PtrArg->getName() << "' because it would require adding more"
173                << " than " << maxElements << " arguments to the function.\n");
174          continue;
175        }
176
177        // If all the elements are single-value types, we can promote it.
178        bool AllSimple = true;
179        for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
180          if (!STy->getElementType(i)->isSingleValueType()) {
181            AllSimple = false;
182            break;
183          }
184        }
185
186        // Safe to transform, don't even bother trying to "promote" it.
187        // Passing the elements as a scalar will allow scalarrepl to hack on
188        // the new alloca we introduce.
189        if (AllSimple) {
190          ByValArgsToTransform.insert(PtrArg);
191          continue;
192        }
193      }
194    }
195
196    // If the argument is a recursive type and we're in a recursive
197    // function, we could end up infinitely peeling the function argument.
198    if (isSelfRecursive) {
199      if (StructType *STy = dyn_cast<StructType>(AgTy)) {
200        bool RecursiveType = false;
201        for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
202          if (STy->getElementType(i) == PtrArg->getType()) {
203            RecursiveType = true;
204            break;
205          }
206        }
207        if (RecursiveType)
208          continue;
209      }
210    }
211
212    // Otherwise, see if we can promote the pointer to its value.
213    if (isSafeToPromoteArgument(PtrArg, PtrArg->hasByValOrInAllocaAttr()))
214      ArgsToPromote.insert(PtrArg);
215  }
216
217  // No promotable pointer arguments.
218  if (ArgsToPromote.empty() && ByValArgsToTransform.empty())
219    return nullptr;
220
221  return DoPromotion(F, ArgsToPromote, ByValArgsToTransform);
222}
223
224/// AllCallersPassInValidPointerForArgument - Return true if we can prove that
225/// all callees pass in a valid pointer for the specified function argument.
226static bool AllCallersPassInValidPointerForArgument(Argument *Arg,
227                                                    const DataLayout *DL) {
228  Function *Callee = Arg->getParent();
229
230  unsigned ArgNo = Arg->getArgNo();
231
232  // Look at all call sites of the function.  At this pointer we know we only
233  // have direct callees.
234  for (User *U : Callee->users()) {
235    CallSite CS(U);
236    assert(CS && "Should only have direct calls!");
237
238    if (!CS.getArgument(ArgNo)->isDereferenceablePointer(DL))
239      return false;
240  }
241  return true;
242}
243
244/// Returns true if Prefix is a prefix of longer. That means, Longer has a size
245/// that is greater than or equal to the size of prefix, and each of the
246/// elements in Prefix is the same as the corresponding elements in Longer.
247///
248/// This means it also returns true when Prefix and Longer are equal!
249static bool IsPrefix(const ArgPromotion::IndicesVector &Prefix,
250                     const ArgPromotion::IndicesVector &Longer) {
251  if (Prefix.size() > Longer.size())
252    return false;
253  return std::equal(Prefix.begin(), Prefix.end(), Longer.begin());
254}
255
256
257/// Checks if Indices, or a prefix of Indices, is in Set.
258static bool PrefixIn(const ArgPromotion::IndicesVector &Indices,
259                     std::set<ArgPromotion::IndicesVector> &Set) {
260    std::set<ArgPromotion::IndicesVector>::iterator Low;
261    Low = Set.upper_bound(Indices);
262    if (Low != Set.begin())
263      Low--;
264    // Low is now the last element smaller than or equal to Indices. This means
265    // it points to a prefix of Indices (possibly Indices itself), if such
266    // prefix exists.
267    //
268    // This load is safe if any prefix of its operands is safe to load.
269    return Low != Set.end() && IsPrefix(*Low, Indices);
270}
271
272/// Mark the given indices (ToMark) as safe in the given set of indices
273/// (Safe). Marking safe usually means adding ToMark to Safe. However, if there
274/// is already a prefix of Indices in Safe, Indices are implicitely marked safe
275/// already. Furthermore, any indices that Indices is itself a prefix of, are
276/// removed from Safe (since they are implicitely safe because of Indices now).
277static void MarkIndicesSafe(const ArgPromotion::IndicesVector &ToMark,
278                            std::set<ArgPromotion::IndicesVector> &Safe) {
279  std::set<ArgPromotion::IndicesVector>::iterator Low;
280  Low = Safe.upper_bound(ToMark);
281  // Guard against the case where Safe is empty
282  if (Low != Safe.begin())
283    Low--;
284  // Low is now the last element smaller than or equal to Indices. This
285  // means it points to a prefix of Indices (possibly Indices itself), if
286  // such prefix exists.
287  if (Low != Safe.end()) {
288    if (IsPrefix(*Low, ToMark))
289      // If there is already a prefix of these indices (or exactly these
290      // indices) marked a safe, don't bother adding these indices
291      return;
292
293    // Increment Low, so we can use it as a "insert before" hint
294    ++Low;
295  }
296  // Insert
297  Low = Safe.insert(Low, ToMark);
298  ++Low;
299  // If there we're a prefix of longer index list(s), remove those
300  std::set<ArgPromotion::IndicesVector>::iterator End = Safe.end();
301  while (Low != End && IsPrefix(ToMark, *Low)) {
302    std::set<ArgPromotion::IndicesVector>::iterator Remove = Low;
303    ++Low;
304    Safe.erase(Remove);
305  }
306}
307
308/// isSafeToPromoteArgument - As you might guess from the name of this method,
309/// it checks to see if it is both safe and useful to promote the argument.
310/// This method limits promotion of aggregates to only promote up to three
311/// elements of the aggregate in order to avoid exploding the number of
312/// arguments passed in.
313bool ArgPromotion::isSafeToPromoteArgument(Argument *Arg,
314                                           bool isByValOrInAlloca) const {
315  typedef std::set<IndicesVector> GEPIndicesSet;
316
317  // Quick exit for unused arguments
318  if (Arg->use_empty())
319    return true;
320
321  // We can only promote this argument if all of the uses are loads, or are GEP
322  // instructions (with constant indices) that are subsequently loaded.
323  //
324  // Promoting the argument causes it to be loaded in the caller
325  // unconditionally. This is only safe if we can prove that either the load
326  // would have happened in the callee anyway (ie, there is a load in the entry
327  // block) or the pointer passed in at every call site is guaranteed to be
328  // valid.
329  // In the former case, invalid loads can happen, but would have happened
330  // anyway, in the latter case, invalid loads won't happen. This prevents us
331  // from introducing an invalid load that wouldn't have happened in the
332  // original code.
333  //
334  // This set will contain all sets of indices that are loaded in the entry
335  // block, and thus are safe to unconditionally load in the caller.
336  //
337  // This optimization is also safe for InAlloca parameters, because it verifies
338  // that the address isn't captured.
339  GEPIndicesSet SafeToUnconditionallyLoad;
340
341  // This set contains all the sets of indices that we are planning to promote.
342  // This makes it possible to limit the number of arguments added.
343  GEPIndicesSet ToPromote;
344
345  // If the pointer is always valid, any load with first index 0 is valid.
346  if (isByValOrInAlloca || AllCallersPassInValidPointerForArgument(Arg, DL))
347    SafeToUnconditionallyLoad.insert(IndicesVector(1, 0));
348
349  // First, iterate the entry block and mark loads of (geps of) arguments as
350  // safe.
351  BasicBlock *EntryBlock = Arg->getParent()->begin();
352  // Declare this here so we can reuse it
353  IndicesVector Indices;
354  for (BasicBlock::iterator I = EntryBlock->begin(), E = EntryBlock->end();
355       I != E; ++I)
356    if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
357      Value *V = LI->getPointerOperand();
358      if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(V)) {
359        V = GEP->getPointerOperand();
360        if (V == Arg) {
361          // This load actually loads (part of) Arg? Check the indices then.
362          Indices.reserve(GEP->getNumIndices());
363          for (User::op_iterator II = GEP->idx_begin(), IE = GEP->idx_end();
364               II != IE; ++II)
365            if (ConstantInt *CI = dyn_cast<ConstantInt>(*II))
366              Indices.push_back(CI->getSExtValue());
367            else
368              // We found a non-constant GEP index for this argument? Bail out
369              // right away, can't promote this argument at all.
370              return false;
371
372          // Indices checked out, mark them as safe
373          MarkIndicesSafe(Indices, SafeToUnconditionallyLoad);
374          Indices.clear();
375        }
376      } else if (V == Arg) {
377        // Direct loads are equivalent to a GEP with a single 0 index.
378        MarkIndicesSafe(IndicesVector(1, 0), SafeToUnconditionallyLoad);
379      }
380    }
381
382  // Now, iterate all uses of the argument to see if there are any uses that are
383  // not (GEP+)loads, or any (GEP+)loads that are not safe to promote.
384  SmallVector<LoadInst*, 16> Loads;
385  IndicesVector Operands;
386  for (Use &U : Arg->uses()) {
387    User *UR = U.getUser();
388    Operands.clear();
389    if (LoadInst *LI = dyn_cast<LoadInst>(UR)) {
390      // Don't hack volatile/atomic loads
391      if (!LI->isSimple()) return false;
392      Loads.push_back(LI);
393      // Direct loads are equivalent to a GEP with a zero index and then a load.
394      Operands.push_back(0);
395    } else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(UR)) {
396      if (GEP->use_empty()) {
397        // Dead GEP's cause trouble later.  Just remove them if we run into
398        // them.
399        getAnalysis<AliasAnalysis>().deleteValue(GEP);
400        GEP->eraseFromParent();
401        // TODO: This runs the above loop over and over again for dead GEPs
402        // Couldn't we just do increment the UI iterator earlier and erase the
403        // use?
404        return isSafeToPromoteArgument(Arg, isByValOrInAlloca);
405      }
406
407      // Ensure that all of the indices are constants.
408      for (User::op_iterator i = GEP->idx_begin(), e = GEP->idx_end();
409        i != e; ++i)
410        if (ConstantInt *C = dyn_cast<ConstantInt>(*i))
411          Operands.push_back(C->getSExtValue());
412        else
413          return false;  // Not a constant operand GEP!
414
415      // Ensure that the only users of the GEP are load instructions.
416      for (User *GEPU : GEP->users())
417        if (LoadInst *LI = dyn_cast<LoadInst>(GEPU)) {
418          // Don't hack volatile/atomic loads
419          if (!LI->isSimple()) return false;
420          Loads.push_back(LI);
421        } else {
422          // Other uses than load?
423          return false;
424        }
425    } else {
426      return false;  // Not a load or a GEP.
427    }
428
429    // Now, see if it is safe to promote this load / loads of this GEP. Loading
430    // is safe if Operands, or a prefix of Operands, is marked as safe.
431    if (!PrefixIn(Operands, SafeToUnconditionallyLoad))
432      return false;
433
434    // See if we are already promoting a load with these indices. If not, check
435    // to make sure that we aren't promoting too many elements.  If so, nothing
436    // to do.
437    if (ToPromote.find(Operands) == ToPromote.end()) {
438      if (maxElements > 0 && ToPromote.size() == maxElements) {
439        DEBUG(dbgs() << "argpromotion not promoting argument '"
440              << Arg->getName() << "' because it would require adding more "
441              << "than " << maxElements << " arguments to the function.\n");
442        // We limit aggregate promotion to only promoting up to a fixed number
443        // of elements of the aggregate.
444        return false;
445      }
446      ToPromote.insert(Operands);
447    }
448  }
449
450  if (Loads.empty()) return true;  // No users, this is a dead argument.
451
452  // Okay, now we know that the argument is only used by load instructions and
453  // it is safe to unconditionally perform all of them. Use alias analysis to
454  // check to see if the pointer is guaranteed to not be modified from entry of
455  // the function to each of the load instructions.
456
457  // Because there could be several/many load instructions, remember which
458  // blocks we know to be transparent to the load.
459  SmallPtrSet<BasicBlock*, 16> TranspBlocks;
460
461  AliasAnalysis &AA = getAnalysis<AliasAnalysis>();
462
463  for (unsigned i = 0, e = Loads.size(); i != e; ++i) {
464    // Check to see if the load is invalidated from the start of the block to
465    // the load itself.
466    LoadInst *Load = Loads[i];
467    BasicBlock *BB = Load->getParent();
468
469    AliasAnalysis::Location Loc = AA.getLocation(Load);
470    if (AA.canInstructionRangeModify(BB->front(), *Load, Loc))
471      return false;  // Pointer is invalidated!
472
473    // Now check every path from the entry block to the load for transparency.
474    // To do this, we perform a depth first search on the inverse CFG from the
475    // loading block.
476    for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
477      BasicBlock *P = *PI;
478      for (idf_ext_iterator<BasicBlock*, SmallPtrSet<BasicBlock*, 16> >
479             I = idf_ext_begin(P, TranspBlocks),
480             E = idf_ext_end(P, TranspBlocks); I != E; ++I)
481        if (AA.canBasicBlockModify(**I, Loc))
482          return false;
483    }
484  }
485
486  // If the path from the entry of the function to each load is free of
487  // instructions that potentially invalidate the load, we can make the
488  // transformation!
489  return true;
490}
491
492/// DoPromotion - This method actually performs the promotion of the specified
493/// arguments, and returns the new function.  At this point, we know that it's
494/// safe to do so.
495CallGraphNode *ArgPromotion::DoPromotion(Function *F,
496                               SmallPtrSet<Argument*, 8> &ArgsToPromote,
497                              SmallPtrSet<Argument*, 8> &ByValArgsToTransform) {
498
499  // Start by computing a new prototype for the function, which is the same as
500  // the old function, but has modified arguments.
501  FunctionType *FTy = F->getFunctionType();
502  std::vector<Type*> Params;
503
504  typedef std::set<IndicesVector> ScalarizeTable;
505
506  // ScalarizedElements - If we are promoting a pointer that has elements
507  // accessed out of it, keep track of which elements are accessed so that we
508  // can add one argument for each.
509  //
510  // Arguments that are directly loaded will have a zero element value here, to
511  // handle cases where there are both a direct load and GEP accesses.
512  //
513  std::map<Argument*, ScalarizeTable> ScalarizedElements;
514
515  // OriginalLoads - Keep track of a representative load instruction from the
516  // original function so that we can tell the alias analysis implementation
517  // what the new GEP/Load instructions we are inserting look like.
518  // We need to keep the original loads for each argument and the elements
519  // of the argument that are accessed.
520  std::map<std::pair<Argument*, IndicesVector>, LoadInst*> OriginalLoads;
521
522  // Attribute - Keep track of the parameter attributes for the arguments
523  // that we are *not* promoting. For the ones that we do promote, the parameter
524  // attributes are lost
525  SmallVector<AttributeSet, 8> AttributesVec;
526  const AttributeSet &PAL = F->getAttributes();
527
528  // Add any return attributes.
529  if (PAL.hasAttributes(AttributeSet::ReturnIndex))
530    AttributesVec.push_back(AttributeSet::get(F->getContext(),
531                                              PAL.getRetAttributes()));
532
533  // First, determine the new argument list
534  unsigned ArgIndex = 1;
535  for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); I != E;
536       ++I, ++ArgIndex) {
537    if (ByValArgsToTransform.count(I)) {
538      // Simple byval argument? Just add all the struct element types.
539      Type *AgTy = cast<PointerType>(I->getType())->getElementType();
540      StructType *STy = cast<StructType>(AgTy);
541      for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i)
542        Params.push_back(STy->getElementType(i));
543      ++NumByValArgsPromoted;
544    } else if (!ArgsToPromote.count(I)) {
545      // Unchanged argument
546      Params.push_back(I->getType());
547      AttributeSet attrs = PAL.getParamAttributes(ArgIndex);
548      if (attrs.hasAttributes(ArgIndex)) {
549        AttrBuilder B(attrs, ArgIndex);
550        AttributesVec.
551          push_back(AttributeSet::get(F->getContext(), Params.size(), B));
552      }
553    } else if (I->use_empty()) {
554      // Dead argument (which are always marked as promotable)
555      ++NumArgumentsDead;
556    } else {
557      // Okay, this is being promoted. This means that the only uses are loads
558      // or GEPs which are only used by loads
559
560      // In this table, we will track which indices are loaded from the argument
561      // (where direct loads are tracked as no indices).
562      ScalarizeTable &ArgIndices = ScalarizedElements[I];
563      for (User *U : I->users()) {
564        Instruction *UI = cast<Instruction>(U);
565        assert(isa<LoadInst>(UI) || isa<GetElementPtrInst>(UI));
566        IndicesVector Indices;
567        Indices.reserve(UI->getNumOperands() - 1);
568        // Since loads will only have a single operand, and GEPs only a single
569        // non-index operand, this will record direct loads without any indices,
570        // and gep+loads with the GEP indices.
571        for (User::op_iterator II = UI->op_begin() + 1, IE = UI->op_end();
572             II != IE; ++II)
573          Indices.push_back(cast<ConstantInt>(*II)->getSExtValue());
574        // GEPs with a single 0 index can be merged with direct loads
575        if (Indices.size() == 1 && Indices.front() == 0)
576          Indices.clear();
577        ArgIndices.insert(Indices);
578        LoadInst *OrigLoad;
579        if (LoadInst *L = dyn_cast<LoadInst>(UI))
580          OrigLoad = L;
581        else
582          // Take any load, we will use it only to update Alias Analysis
583          OrigLoad = cast<LoadInst>(UI->user_back());
584        OriginalLoads[std::make_pair(I, Indices)] = OrigLoad;
585      }
586
587      // Add a parameter to the function for each element passed in.
588      for (ScalarizeTable::iterator SI = ArgIndices.begin(),
589             E = ArgIndices.end(); SI != E; ++SI) {
590        // not allowed to dereference ->begin() if size() is 0
591        Params.push_back(GetElementPtrInst::getIndexedType(I->getType(), *SI));
592        assert(Params.back());
593      }
594
595      if (ArgIndices.size() == 1 && ArgIndices.begin()->empty())
596        ++NumArgumentsPromoted;
597      else
598        ++NumAggregatesPromoted;
599    }
600  }
601
602  // Add any function attributes.
603  if (PAL.hasAttributes(AttributeSet::FunctionIndex))
604    AttributesVec.push_back(AttributeSet::get(FTy->getContext(),
605                                              PAL.getFnAttributes()));
606
607  Type *RetTy = FTy->getReturnType();
608
609  // Construct the new function type using the new arguments.
610  FunctionType *NFTy = FunctionType::get(RetTy, Params, FTy->isVarArg());
611
612  // Create the new function body and insert it into the module.
613  Function *NF = Function::Create(NFTy, F->getLinkage(), F->getName());
614  NF->copyAttributesFrom(F);
615
616  // Patch the pointer to LLVM function in debug info descriptor.
617  auto DI = FunctionDIs.find(F);
618  if (DI != FunctionDIs.end())
619    DI->second.replaceFunction(NF);
620
621  DEBUG(dbgs() << "ARG PROMOTION:  Promoting to:" << *NF << "\n"
622        << "From: " << *F);
623
624  // Recompute the parameter attributes list based on the new arguments for
625  // the function.
626  NF->setAttributes(AttributeSet::get(F->getContext(), AttributesVec));
627  AttributesVec.clear();
628
629  F->getParent()->getFunctionList().insert(F, NF);
630  NF->takeName(F);
631
632  // Get the alias analysis information that we need to update to reflect our
633  // changes.
634  AliasAnalysis &AA = getAnalysis<AliasAnalysis>();
635
636  // Get the callgraph information that we need to update to reflect our
637  // changes.
638  CallGraph &CG = getAnalysis<CallGraphWrapperPass>().getCallGraph();
639
640  // Get a new callgraph node for NF.
641  CallGraphNode *NF_CGN = CG.getOrInsertFunction(NF);
642
643  // Loop over all of the callers of the function, transforming the call sites
644  // to pass in the loaded pointers.
645  //
646  SmallVector<Value*, 16> Args;
647  while (!F->use_empty()) {
648    CallSite CS(F->user_back());
649    assert(CS.getCalledFunction() == F);
650    Instruction *Call = CS.getInstruction();
651    const AttributeSet &CallPAL = CS.getAttributes();
652
653    // Add any return attributes.
654    if (CallPAL.hasAttributes(AttributeSet::ReturnIndex))
655      AttributesVec.push_back(AttributeSet::get(F->getContext(),
656                                                CallPAL.getRetAttributes()));
657
658    // Loop over the operands, inserting GEP and loads in the caller as
659    // appropriate.
660    CallSite::arg_iterator AI = CS.arg_begin();
661    ArgIndex = 1;
662    for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end();
663         I != E; ++I, ++AI, ++ArgIndex)
664      if (!ArgsToPromote.count(I) && !ByValArgsToTransform.count(I)) {
665        Args.push_back(*AI);          // Unmodified argument
666
667        if (CallPAL.hasAttributes(ArgIndex)) {
668          AttrBuilder B(CallPAL, ArgIndex);
669          AttributesVec.
670            push_back(AttributeSet::get(F->getContext(), Args.size(), B));
671        }
672      } else if (ByValArgsToTransform.count(I)) {
673        // Emit a GEP and load for each element of the struct.
674        Type *AgTy = cast<PointerType>(I->getType())->getElementType();
675        StructType *STy = cast<StructType>(AgTy);
676        Value *Idxs[2] = {
677              ConstantInt::get(Type::getInt32Ty(F->getContext()), 0), nullptr };
678        for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
679          Idxs[1] = ConstantInt::get(Type::getInt32Ty(F->getContext()), i);
680          Value *Idx = GetElementPtrInst::Create(*AI, Idxs,
681                                                 (*AI)->getName()+"."+utostr(i),
682                                                 Call);
683          // TODO: Tell AA about the new values?
684          Args.push_back(new LoadInst(Idx, Idx->getName()+".val", Call));
685        }
686      } else if (!I->use_empty()) {
687        // Non-dead argument: insert GEPs and loads as appropriate.
688        ScalarizeTable &ArgIndices = ScalarizedElements[I];
689        // Store the Value* version of the indices in here, but declare it now
690        // for reuse.
691        std::vector<Value*> Ops;
692        for (ScalarizeTable::iterator SI = ArgIndices.begin(),
693               E = ArgIndices.end(); SI != E; ++SI) {
694          Value *V = *AI;
695          LoadInst *OrigLoad = OriginalLoads[std::make_pair(I, *SI)];
696          if (!SI->empty()) {
697            Ops.reserve(SI->size());
698            Type *ElTy = V->getType();
699            for (IndicesVector::const_iterator II = SI->begin(),
700                 IE = SI->end(); II != IE; ++II) {
701              // Use i32 to index structs, and i64 for others (pointers/arrays).
702              // This satisfies GEP constraints.
703              Type *IdxTy = (ElTy->isStructTy() ?
704                    Type::getInt32Ty(F->getContext()) :
705                    Type::getInt64Ty(F->getContext()));
706              Ops.push_back(ConstantInt::get(IdxTy, *II));
707              // Keep track of the type we're currently indexing.
708              ElTy = cast<CompositeType>(ElTy)->getTypeAtIndex(*II);
709            }
710            // And create a GEP to extract those indices.
711            V = GetElementPtrInst::Create(V, Ops, V->getName()+".idx", Call);
712            Ops.clear();
713            AA.copyValue(OrigLoad->getOperand(0), V);
714          }
715          // Since we're replacing a load make sure we take the alignment
716          // of the previous load.
717          LoadInst *newLoad = new LoadInst(V, V->getName()+".val", Call);
718          newLoad->setAlignment(OrigLoad->getAlignment());
719          // Transfer the TBAA info too.
720          newLoad->setMetadata(LLVMContext::MD_tbaa,
721                               OrigLoad->getMetadata(LLVMContext::MD_tbaa));
722          Args.push_back(newLoad);
723          AA.copyValue(OrigLoad, Args.back());
724        }
725      }
726
727    // Push any varargs arguments on the list.
728    for (; AI != CS.arg_end(); ++AI, ++ArgIndex) {
729      Args.push_back(*AI);
730      if (CallPAL.hasAttributes(ArgIndex)) {
731        AttrBuilder B(CallPAL, ArgIndex);
732        AttributesVec.
733          push_back(AttributeSet::get(F->getContext(), Args.size(), B));
734      }
735    }
736
737    // Add any function attributes.
738    if (CallPAL.hasAttributes(AttributeSet::FunctionIndex))
739      AttributesVec.push_back(AttributeSet::get(Call->getContext(),
740                                                CallPAL.getFnAttributes()));
741
742    Instruction *New;
743    if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) {
744      New = InvokeInst::Create(NF, II->getNormalDest(), II->getUnwindDest(),
745                               Args, "", Call);
746      cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv());
747      cast<InvokeInst>(New)->setAttributes(AttributeSet::get(II->getContext(),
748                                                            AttributesVec));
749    } else {
750      New = CallInst::Create(NF, Args, "", Call);
751      cast<CallInst>(New)->setCallingConv(CS.getCallingConv());
752      cast<CallInst>(New)->setAttributes(AttributeSet::get(New->getContext(),
753                                                          AttributesVec));
754      if (cast<CallInst>(Call)->isTailCall())
755        cast<CallInst>(New)->setTailCall();
756    }
757    New->setDebugLoc(Call->getDebugLoc());
758    Args.clear();
759    AttributesVec.clear();
760
761    // Update the alias analysis implementation to know that we are replacing
762    // the old call with a new one.
763    AA.replaceWithNewValue(Call, New);
764
765    // Update the callgraph to know that the callsite has been transformed.
766    CallGraphNode *CalleeNode = CG[Call->getParent()->getParent()];
767    CalleeNode->replaceCallEdge(Call, New, NF_CGN);
768
769    if (!Call->use_empty()) {
770      Call->replaceAllUsesWith(New);
771      New->takeName(Call);
772    }
773
774    // Finally, remove the old call from the program, reducing the use-count of
775    // F.
776    Call->eraseFromParent();
777  }
778
779  // Since we have now created the new function, splice the body of the old
780  // function right into the new function, leaving the old rotting hulk of the
781  // function empty.
782  NF->getBasicBlockList().splice(NF->begin(), F->getBasicBlockList());
783
784  // Loop over the argument list, transferring uses of the old arguments over to
785  // the new arguments, also transferring over the names as well.
786  //
787  for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(),
788       I2 = NF->arg_begin(); I != E; ++I) {
789    if (!ArgsToPromote.count(I) && !ByValArgsToTransform.count(I)) {
790      // If this is an unmodified argument, move the name and users over to the
791      // new version.
792      I->replaceAllUsesWith(I2);
793      I2->takeName(I);
794      AA.replaceWithNewValue(I, I2);
795      ++I2;
796      continue;
797    }
798
799    if (ByValArgsToTransform.count(I)) {
800      // In the callee, we create an alloca, and store each of the new incoming
801      // arguments into the alloca.
802      Instruction *InsertPt = NF->begin()->begin();
803
804      // Just add all the struct element types.
805      Type *AgTy = cast<PointerType>(I->getType())->getElementType();
806      Value *TheAlloca = new AllocaInst(AgTy, nullptr, "", InsertPt);
807      StructType *STy = cast<StructType>(AgTy);
808      Value *Idxs[2] = {
809            ConstantInt::get(Type::getInt32Ty(F->getContext()), 0), nullptr };
810
811      for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
812        Idxs[1] = ConstantInt::get(Type::getInt32Ty(F->getContext()), i);
813        Value *Idx =
814          GetElementPtrInst::Create(TheAlloca, Idxs,
815                                    TheAlloca->getName()+"."+Twine(i),
816                                    InsertPt);
817        I2->setName(I->getName()+"."+Twine(i));
818        new StoreInst(I2++, Idx, InsertPt);
819      }
820
821      // Anything that used the arg should now use the alloca.
822      I->replaceAllUsesWith(TheAlloca);
823      TheAlloca->takeName(I);
824      AA.replaceWithNewValue(I, TheAlloca);
825
826      // If the alloca is used in a call, we must clear the tail flag since
827      // the callee now uses an alloca from the caller.
828      for (User *U : TheAlloca->users()) {
829        CallInst *Call = dyn_cast<CallInst>(U);
830        if (!Call)
831          continue;
832        Call->setTailCall(false);
833      }
834      continue;
835    }
836
837    if (I->use_empty()) {
838      AA.deleteValue(I);
839      continue;
840    }
841
842    // Otherwise, if we promoted this argument, then all users are load
843    // instructions (or GEPs with only load users), and all loads should be
844    // using the new argument that we added.
845    ScalarizeTable &ArgIndices = ScalarizedElements[I];
846
847    while (!I->use_empty()) {
848      if (LoadInst *LI = dyn_cast<LoadInst>(I->user_back())) {
849        assert(ArgIndices.begin()->empty() &&
850               "Load element should sort to front!");
851        I2->setName(I->getName()+".val");
852        LI->replaceAllUsesWith(I2);
853        AA.replaceWithNewValue(LI, I2);
854        LI->eraseFromParent();
855        DEBUG(dbgs() << "*** Promoted load of argument '" << I->getName()
856              << "' in function '" << F->getName() << "'\n");
857      } else {
858        GetElementPtrInst *GEP = cast<GetElementPtrInst>(I->user_back());
859        IndicesVector Operands;
860        Operands.reserve(GEP->getNumIndices());
861        for (User::op_iterator II = GEP->idx_begin(), IE = GEP->idx_end();
862             II != IE; ++II)
863          Operands.push_back(cast<ConstantInt>(*II)->getSExtValue());
864
865        // GEPs with a single 0 index can be merged with direct loads
866        if (Operands.size() == 1 && Operands.front() == 0)
867          Operands.clear();
868
869        Function::arg_iterator TheArg = I2;
870        for (ScalarizeTable::iterator It = ArgIndices.begin();
871             *It != Operands; ++It, ++TheArg) {
872          assert(It != ArgIndices.end() && "GEP not handled??");
873        }
874
875        std::string NewName = I->getName();
876        for (unsigned i = 0, e = Operands.size(); i != e; ++i) {
877            NewName += "." + utostr(Operands[i]);
878        }
879        NewName += ".val";
880        TheArg->setName(NewName);
881
882        DEBUG(dbgs() << "*** Promoted agg argument '" << TheArg->getName()
883              << "' of function '" << NF->getName() << "'\n");
884
885        // All of the uses must be load instructions.  Replace them all with
886        // the argument specified by ArgNo.
887        while (!GEP->use_empty()) {
888          LoadInst *L = cast<LoadInst>(GEP->user_back());
889          L->replaceAllUsesWith(TheArg);
890          AA.replaceWithNewValue(L, TheArg);
891          L->eraseFromParent();
892        }
893        AA.deleteValue(GEP);
894        GEP->eraseFromParent();
895      }
896    }
897
898    // Increment I2 past all of the arguments added for this promoted pointer.
899    std::advance(I2, ArgIndices.size());
900  }
901
902  // Tell the alias analysis that the old function is about to disappear.
903  AA.replaceWithNewValue(F, NF);
904
905
906  NF_CGN->stealCalledFunctionsFrom(CG[F]);
907
908  // Now that the old function is dead, delete it.  If there is a dangling
909  // reference to the CallgraphNode, just leave the dead function around for
910  // someone else to nuke.
911  CallGraphNode *CGN = CG[F];
912  if (CGN->getNumReferences() == 0)
913    delete CG.removeFunctionFromModule(CGN);
914  else
915    F->setLinkage(Function::ExternalLinkage);
916
917  return NF_CGN;
918}
919
920bool ArgPromotion::doInitialization(CallGraph &CG) {
921  FunctionDIs = makeSubprogramMap(CG.getModule());
922  return CallGraphSCCPass::doInitialization(CG);
923}
924