1 //===-- ArgumentPromotion.cpp - Promote by-reference arguments ------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
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).
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.
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.
30 //===----------------------------------------------------------------------===//
32 #define DEBUG_TYPE "argpromotion"
33 #include "llvm/Transforms/IPO.h"
34 #include "llvm/Constants.h"
35 #include "llvm/DerivedTypes.h"
36 #include "llvm/Module.h"
37 #include "llvm/CallGraphSCCPass.h"
38 #include "llvm/Instructions.h"
39 #include "llvm/LLVMContext.h"
40 #include "llvm/Analysis/AliasAnalysis.h"
41 #include "llvm/Analysis/CallGraph.h"
42 #include "llvm/Target/TargetData.h"
43 #include "llvm/Support/CallSite.h"
44 #include "llvm/Support/CFG.h"
45 #include "llvm/Support/Debug.h"
46 #include "llvm/Support/raw_ostream.h"
47 #include "llvm/ADT/DepthFirstIterator.h"
48 #include "llvm/ADT/Statistic.h"
49 #include "llvm/ADT/StringExtras.h"
53 STATISTIC(NumArgumentsPromoted
, "Number of pointer arguments promoted");
54 STATISTIC(NumAggregatesPromoted
, "Number of aggregate arguments promoted");
55 STATISTIC(NumByValArgsPromoted
, "Number of byval arguments promoted");
56 STATISTIC(NumArgumentsDead
, "Number of dead pointer args eliminated");
59 /// ArgPromotion - The 'by reference' to 'by value' argument promotion pass.
61 struct ArgPromotion
: public CallGraphSCCPass
{
62 virtual void getAnalysisUsage(AnalysisUsage
&AU
) const {
63 AU
.addRequired
<AliasAnalysis
>();
64 CallGraphSCCPass::getAnalysisUsage(AU
);
67 virtual bool runOnSCC(std::vector
<CallGraphNode
*> &SCC
);
68 static char ID
; // Pass identification, replacement for typeid
69 explicit ArgPromotion(unsigned maxElements
= 3)
70 : CallGraphSCCPass(&ID
), maxElements(maxElements
) {}
72 /// A vector used to hold the indices of a single GEP instruction
73 typedef std::vector
<uint64_t> IndicesVector
;
76 CallGraphNode
*PromoteArguments(CallGraphNode
*CGN
);
77 bool isSafeToPromoteArgument(Argument
*Arg
, bool isByVal
) const;
78 CallGraphNode
*DoPromotion(Function
*F
,
79 SmallPtrSet
<Argument
*, 8> &ArgsToPromote
,
80 SmallPtrSet
<Argument
*, 8> &ByValArgsToTransform
);
81 /// The maximum number of elements to expand, or 0 for unlimited.
86 char ArgPromotion::ID
= 0;
87 static RegisterPass
<ArgPromotion
>
88 X("argpromotion", "Promote 'by reference' arguments to scalars");
90 Pass
*llvm::createArgumentPromotionPass(unsigned maxElements
) {
91 return new ArgPromotion(maxElements
);
94 bool ArgPromotion::runOnSCC(std::vector
<CallGraphNode
*> &SCC
) {
95 bool Changed
= false, LocalChange
;
97 do { // Iterate until we stop promoting from this SCC.
99 // Attempt to promote arguments from all functions in this SCC.
100 for (unsigned i
= 0, e
= SCC
.size(); i
!= e
; ++i
)
101 if (CallGraphNode
*CGN
= PromoteArguments(SCC
[i
])) {
105 Changed
|= LocalChange
; // Remember that we changed something.
106 } while (LocalChange
);
111 /// PromoteArguments - This method checks the specified function to see if there
112 /// are any promotable arguments and if it is safe to promote the function (for
113 /// example, all callers are direct). If safe to promote some arguments, it
114 /// calls the DoPromotion method.
116 CallGraphNode
*ArgPromotion::PromoteArguments(CallGraphNode
*CGN
) {
117 Function
*F
= CGN
->getFunction();
119 // Make sure that it is local to this module.
120 if (!F
|| !F
->hasLocalLinkage()) return 0;
122 // First check: see if there are any pointer arguments! If not, quick exit.
123 SmallVector
<std::pair
<Argument
*, unsigned>, 16> PointerArgs
;
125 for (Function::arg_iterator I
= F
->arg_begin(), E
= F
->arg_end();
126 I
!= E
; ++I
, ++ArgNo
)
127 if (isa
<PointerType
>(I
->getType()))
128 PointerArgs
.push_back(std::pair
<Argument
*, unsigned>(I
, ArgNo
));
129 if (PointerArgs
.empty()) return 0;
131 // Second check: make sure that all callers are direct callers. We can't
132 // transform functions that have indirect callers.
133 if (F
->hasAddressTaken())
136 // Check to see which arguments are promotable. If an argument is promotable,
137 // add it to ArgsToPromote.
138 SmallPtrSet
<Argument
*, 8> ArgsToPromote
;
139 SmallPtrSet
<Argument
*, 8> ByValArgsToTransform
;
140 for (unsigned i
= 0; i
!= PointerArgs
.size(); ++i
) {
141 bool isByVal
= F
->paramHasAttr(PointerArgs
[i
].second
+1, Attribute::ByVal
);
143 // If this is a byval argument, and if the aggregate type is small, just
144 // pass the elements, which is always safe.
145 Argument
*PtrArg
= PointerArgs
[i
].first
;
147 const Type
*AgTy
= cast
<PointerType
>(PtrArg
->getType())->getElementType();
148 if (const StructType
*STy
= dyn_cast
<StructType
>(AgTy
)) {
149 if (maxElements
> 0 && STy
->getNumElements() > maxElements
) {
150 DEBUG(errs() << "argpromotion disable promoting argument '"
151 << PtrArg
->getName() << "' because it would require adding more"
152 << " than " << maxElements
<< " arguments to the function.\n");
154 // If all the elements are single-value types, we can promote it.
155 bool AllSimple
= true;
156 for (unsigned i
= 0, e
= STy
->getNumElements(); i
!= e
; ++i
)
157 if (!STy
->getElementType(i
)->isSingleValueType()) {
162 // Safe to transform, don't even bother trying to "promote" it.
163 // Passing the elements as a scalar will allow scalarrepl to hack on
164 // the new alloca we introduce.
166 ByValArgsToTransform
.insert(PtrArg
);
173 // Otherwise, see if we can promote the pointer to its value.
174 if (isSafeToPromoteArgument(PtrArg
, isByVal
))
175 ArgsToPromote
.insert(PtrArg
);
178 // No promotable pointer arguments.
179 if (ArgsToPromote
.empty() && ByValArgsToTransform
.empty())
182 return DoPromotion(F
, ArgsToPromote
, ByValArgsToTransform
);
185 /// IsAlwaysValidPointer - Return true if the specified pointer is always legal
187 static bool IsAlwaysValidPointer(Value
*V
) {
188 if (isa
<AllocaInst
>(V
) || isa
<GlobalVariable
>(V
)) return true;
189 if (GetElementPtrInst
*GEP
= dyn_cast
<GetElementPtrInst
>(V
))
190 return IsAlwaysValidPointer(GEP
->getOperand(0));
191 if (ConstantExpr
*CE
= dyn_cast
<ConstantExpr
>(V
))
192 if (CE
->getOpcode() == Instruction::GetElementPtr
)
193 return IsAlwaysValidPointer(CE
->getOperand(0));
198 /// AllCalleesPassInValidPointerForArgument - Return true if we can prove that
199 /// all callees pass in a valid pointer for the specified function argument.
200 static bool AllCalleesPassInValidPointerForArgument(Argument
*Arg
) {
201 Function
*Callee
= Arg
->getParent();
203 unsigned ArgNo
= std::distance(Callee
->arg_begin(),
204 Function::arg_iterator(Arg
));
206 // Look at all call sites of the function. At this pointer we know we only
207 // have direct callees.
208 for (Value::use_iterator UI
= Callee
->use_begin(), E
= Callee
->use_end();
210 CallSite CS
= CallSite::get(*UI
);
211 assert(CS
.getInstruction() && "Should only have direct calls!");
213 if (!IsAlwaysValidPointer(CS
.getArgument(ArgNo
)))
219 /// Returns true if Prefix is a prefix of longer. That means, Longer has a size
220 /// that is greater than or equal to the size of prefix, and each of the
221 /// elements in Prefix is the same as the corresponding elements in Longer.
223 /// This means it also returns true when Prefix and Longer are equal!
224 static bool IsPrefix(const ArgPromotion::IndicesVector
&Prefix
,
225 const ArgPromotion::IndicesVector
&Longer
) {
226 if (Prefix
.size() > Longer
.size())
228 for (unsigned i
= 0, e
= Prefix
.size(); i
!= e
; ++i
)
229 if (Prefix
[i
] != Longer
[i
])
235 /// Checks if Indices, or a prefix of Indices, is in Set.
236 static bool PrefixIn(const ArgPromotion::IndicesVector
&Indices
,
237 std::set
<ArgPromotion::IndicesVector
> &Set
) {
238 std::set
<ArgPromotion::IndicesVector
>::iterator Low
;
239 Low
= Set
.upper_bound(Indices
);
240 if (Low
!= Set
.begin())
242 // Low is now the last element smaller than or equal to Indices. This means
243 // it points to a prefix of Indices (possibly Indices itself), if such
246 // This load is safe if any prefix of its operands is safe to load.
247 return Low
!= Set
.end() && IsPrefix(*Low
, Indices
);
250 /// Mark the given indices (ToMark) as safe in the the given set of indices
251 /// (Safe). Marking safe usually means adding ToMark to Safe. However, if there
252 /// is already a prefix of Indices in Safe, Indices are implicitely marked safe
253 /// already. Furthermore, any indices that Indices is itself a prefix of, are
254 /// removed from Safe (since they are implicitely safe because of Indices now).
255 static void MarkIndicesSafe(const ArgPromotion::IndicesVector
&ToMark
,
256 std::set
<ArgPromotion::IndicesVector
> &Safe
) {
257 std::set
<ArgPromotion::IndicesVector
>::iterator Low
;
258 Low
= Safe
.upper_bound(ToMark
);
259 // Guard against the case where Safe is empty
260 if (Low
!= Safe
.begin())
262 // Low is now the last element smaller than or equal to Indices. This
263 // means it points to a prefix of Indices (possibly Indices itself), if
264 // such prefix exists.
265 if (Low
!= Safe
.end()) {
266 if (IsPrefix(*Low
, ToMark
))
267 // If there is already a prefix of these indices (or exactly these
268 // indices) marked a safe, don't bother adding these indices
271 // Increment Low, so we can use it as a "insert before" hint
275 Low
= Safe
.insert(Low
, ToMark
);
277 // If there we're a prefix of longer index list(s), remove those
278 std::set
<ArgPromotion::IndicesVector
>::iterator End
= Safe
.end();
279 while (Low
!= End
&& IsPrefix(ToMark
, *Low
)) {
280 std::set
<ArgPromotion::IndicesVector
>::iterator Remove
= Low
;
286 /// isSafeToPromoteArgument - As you might guess from the name of this method,
287 /// it checks to see if it is both safe and useful to promote the argument.
288 /// This method limits promotion of aggregates to only promote up to three
289 /// elements of the aggregate in order to avoid exploding the number of
290 /// arguments passed in.
291 bool ArgPromotion::isSafeToPromoteArgument(Argument
*Arg
, bool isByVal
) const {
292 typedef std::set
<IndicesVector
> GEPIndicesSet
;
294 // Quick exit for unused arguments
295 if (Arg
->use_empty())
298 // We can only promote this argument if all of the uses are loads, or are GEP
299 // instructions (with constant indices) that are subsequently loaded.
301 // Promoting the argument causes it to be loaded in the caller
302 // unconditionally. This is only safe if we can prove that either the load
303 // would have happened in the callee anyway (ie, there is a load in the entry
304 // block) or the pointer passed in at every call site is guaranteed to be
306 // In the former case, invalid loads can happen, but would have happened
307 // anyway, in the latter case, invalid loads won't happen. This prevents us
308 // from introducing an invalid load that wouldn't have happened in the
311 // This set will contain all sets of indices that are loaded in the entry
312 // block, and thus are safe to unconditionally load in the caller.
313 GEPIndicesSet SafeToUnconditionallyLoad
;
315 // This set contains all the sets of indices that we are planning to promote.
316 // This makes it possible to limit the number of arguments added.
317 GEPIndicesSet ToPromote
;
319 // If the pointer is always valid, any load with first index 0 is valid.
320 if(isByVal
|| AllCalleesPassInValidPointerForArgument(Arg
))
321 SafeToUnconditionallyLoad
.insert(IndicesVector(1, 0));
323 // First, iterate the entry block and mark loads of (geps of) arguments as
325 BasicBlock
*EntryBlock
= Arg
->getParent()->begin();
326 // Declare this here so we can reuse it
327 IndicesVector Indices
;
328 for (BasicBlock::iterator I
= EntryBlock
->begin(), E
= EntryBlock
->end();
330 if (LoadInst
*LI
= dyn_cast
<LoadInst
>(I
)) {
331 Value
*V
= LI
->getPointerOperand();
332 if (GetElementPtrInst
*GEP
= dyn_cast
<GetElementPtrInst
>(V
)) {
333 V
= GEP
->getPointerOperand();
335 // This load actually loads (part of) Arg? Check the indices then.
336 Indices
.reserve(GEP
->getNumIndices());
337 for (User::op_iterator II
= GEP
->idx_begin(), IE
= GEP
->idx_end();
339 if (ConstantInt
*CI
= dyn_cast
<ConstantInt
>(*II
))
340 Indices
.push_back(CI
->getSExtValue());
342 // We found a non-constant GEP index for this argument? Bail out
343 // right away, can't promote this argument at all.
346 // Indices checked out, mark them as safe
347 MarkIndicesSafe(Indices
, SafeToUnconditionallyLoad
);
350 } else if (V
== Arg
) {
351 // Direct loads are equivalent to a GEP with a single 0 index.
352 MarkIndicesSafe(IndicesVector(1, 0), SafeToUnconditionallyLoad
);
356 // Now, iterate all uses of the argument to see if there are any uses that are
357 // not (GEP+)loads, or any (GEP+)loads that are not safe to promote.
358 SmallVector
<LoadInst
*, 16> Loads
;
359 IndicesVector Operands
;
360 for (Value::use_iterator UI
= Arg
->use_begin(), E
= Arg
->use_end();
363 if (LoadInst
*LI
= dyn_cast
<LoadInst
>(*UI
)) {
364 if (LI
->isVolatile()) return false; // Don't hack volatile loads
366 // Direct loads are equivalent to a GEP with a zero index and then a load.
367 Operands
.push_back(0);
368 } else if (GetElementPtrInst
*GEP
= dyn_cast
<GetElementPtrInst
>(*UI
)) {
369 if (GEP
->use_empty()) {
370 // Dead GEP's cause trouble later. Just remove them if we run into
372 getAnalysis
<AliasAnalysis
>().deleteValue(GEP
);
373 GEP
->eraseFromParent();
374 // TODO: This runs the above loop over and over again for dead GEPS
375 // Couldn't we just do increment the UI iterator earlier and erase the
377 return isSafeToPromoteArgument(Arg
, isByVal
);
380 // Ensure that all of the indices are constants.
381 for (User::op_iterator i
= GEP
->idx_begin(), e
= GEP
->idx_end();
383 if (ConstantInt
*C
= dyn_cast
<ConstantInt
>(*i
))
384 Operands
.push_back(C
->getSExtValue());
386 return false; // Not a constant operand GEP!
388 // Ensure that the only users of the GEP are load instructions.
389 for (Value::use_iterator UI
= GEP
->use_begin(), E
= GEP
->use_end();
391 if (LoadInst
*LI
= dyn_cast
<LoadInst
>(*UI
)) {
392 if (LI
->isVolatile()) return false; // Don't hack volatile loads
395 // Other uses than load?
399 return false; // Not a load or a GEP.
402 // Now, see if it is safe to promote this load / loads of this GEP. Loading
403 // is safe if Operands, or a prefix of Operands, is marked as safe.
404 if (!PrefixIn(Operands
, SafeToUnconditionallyLoad
))
407 // See if we are already promoting a load with these indices. If not, check
408 // to make sure that we aren't promoting too many elements. If so, nothing
410 if (ToPromote
.find(Operands
) == ToPromote
.end()) {
411 if (maxElements
> 0 && ToPromote
.size() == maxElements
) {
412 DEBUG(errs() << "argpromotion not promoting argument '"
413 << Arg
->getName() << "' because it would require adding more "
414 << "than " << maxElements
<< " arguments to the function.\n");
415 // We limit aggregate promotion to only promoting up to a fixed number
416 // of elements of the aggregate.
419 ToPromote
.insert(Operands
);
423 if (Loads
.empty()) return true; // No users, this is a dead argument.
425 // Okay, now we know that the argument is only used by load instructions and
426 // it is safe to unconditionally perform all of them. Use alias analysis to
427 // check to see if the pointer is guaranteed to not be modified from entry of
428 // the function to each of the load instructions.
430 // Because there could be several/many load instructions, remember which
431 // blocks we know to be transparent to the load.
432 SmallPtrSet
<BasicBlock
*, 16> TranspBlocks
;
434 AliasAnalysis
&AA
= getAnalysis
<AliasAnalysis
>();
435 TargetData
*TD
= getAnalysisIfAvailable
<TargetData
>();
436 if (!TD
) return false; // Without TargetData, assume the worst.
438 for (unsigned i
= 0, e
= Loads
.size(); i
!= e
; ++i
) {
439 // Check to see if the load is invalidated from the start of the block to
441 LoadInst
*Load
= Loads
[i
];
442 BasicBlock
*BB
= Load
->getParent();
444 const PointerType
*LoadTy
=
445 cast
<PointerType
>(Load
->getPointerOperand()->getType());
446 unsigned LoadSize
=(unsigned)TD
->getTypeStoreSize(LoadTy
->getElementType());
448 if (AA
.canInstructionRangeModify(BB
->front(), *Load
, Arg
, LoadSize
))
449 return false; // Pointer is invalidated!
451 // Now check every path from the entry block to the load for transparency.
452 // To do this, we perform a depth first search on the inverse CFG from the
454 for (pred_iterator PI
= pred_begin(BB
), E
= pred_end(BB
); PI
!= E
; ++PI
)
455 for (idf_ext_iterator
<BasicBlock
*, SmallPtrSet
<BasicBlock
*, 16> >
456 I
= idf_ext_begin(*PI
, TranspBlocks
),
457 E
= idf_ext_end(*PI
, TranspBlocks
); I
!= E
; ++I
)
458 if (AA
.canBasicBlockModify(**I
, Arg
, LoadSize
))
462 // If the path from the entry of the function to each load is free of
463 // instructions that potentially invalidate the load, we can make the
468 /// DoPromotion - This method actually performs the promotion of the specified
469 /// arguments, and returns the new function. At this point, we know that it's
471 CallGraphNode
*ArgPromotion::DoPromotion(Function
*F
,
472 SmallPtrSet
<Argument
*, 8> &ArgsToPromote
,
473 SmallPtrSet
<Argument
*, 8> &ByValArgsToTransform
) {
475 // Start by computing a new prototype for the function, which is the same as
476 // the old function, but has modified arguments.
477 const FunctionType
*FTy
= F
->getFunctionType();
478 std::vector
<const Type
*> Params
;
480 typedef std::set
<IndicesVector
> ScalarizeTable
;
482 // ScalarizedElements - If we are promoting a pointer that has elements
483 // accessed out of it, keep track of which elements are accessed so that we
484 // can add one argument for each.
486 // Arguments that are directly loaded will have a zero element value here, to
487 // handle cases where there are both a direct load and GEP accesses.
489 std::map
<Argument
*, ScalarizeTable
> ScalarizedElements
;
491 // OriginalLoads - Keep track of a representative load instruction from the
492 // original function so that we can tell the alias analysis implementation
493 // what the new GEP/Load instructions we are inserting look like.
494 std::map
<IndicesVector
, LoadInst
*> OriginalLoads
;
496 // Attributes - Keep track of the parameter attributes for the arguments
497 // that we are *not* promoting. For the ones that we do promote, the parameter
498 // attributes are lost
499 SmallVector
<AttributeWithIndex
, 8> AttributesVec
;
500 const AttrListPtr
&PAL
= F
->getAttributes();
502 // Add any return attributes.
503 if (Attributes attrs
= PAL
.getRetAttributes())
504 AttributesVec
.push_back(AttributeWithIndex::get(0, attrs
));
506 // First, determine the new argument list
507 unsigned ArgIndex
= 1;
508 for (Function::arg_iterator I
= F
->arg_begin(), E
= F
->arg_end(); I
!= E
;
510 if (ByValArgsToTransform
.count(I
)) {
511 // Simple byval argument? Just add all the struct element types.
512 const Type
*AgTy
= cast
<PointerType
>(I
->getType())->getElementType();
513 const StructType
*STy
= cast
<StructType
>(AgTy
);
514 for (unsigned i
= 0, e
= STy
->getNumElements(); i
!= e
; ++i
)
515 Params
.push_back(STy
->getElementType(i
));
516 ++NumByValArgsPromoted
;
517 } else if (!ArgsToPromote
.count(I
)) {
518 // Unchanged argument
519 Params
.push_back(I
->getType());
520 if (Attributes attrs
= PAL
.getParamAttributes(ArgIndex
))
521 AttributesVec
.push_back(AttributeWithIndex::get(Params
.size(), attrs
));
522 } else if (I
->use_empty()) {
523 // Dead argument (which are always marked as promotable)
526 // Okay, this is being promoted. This means that the only uses are loads
527 // or GEPs which are only used by loads
529 // In this table, we will track which indices are loaded from the argument
530 // (where direct loads are tracked as no indices).
531 ScalarizeTable
&ArgIndices
= ScalarizedElements
[I
];
532 for (Value::use_iterator UI
= I
->use_begin(), E
= I
->use_end(); UI
!= E
;
534 Instruction
*User
= cast
<Instruction
>(*UI
);
535 assert(isa
<LoadInst
>(User
) || isa
<GetElementPtrInst
>(User
));
536 IndicesVector Indices
;
537 Indices
.reserve(User
->getNumOperands() - 1);
538 // Since loads will only have a single operand, and GEPs only a single
539 // non-index operand, this will record direct loads without any indices,
540 // and gep+loads with the GEP indices.
541 for (User::op_iterator II
= User
->op_begin() + 1, IE
= User
->op_end();
543 Indices
.push_back(cast
<ConstantInt
>(*II
)->getSExtValue());
544 // GEPs with a single 0 index can be merged with direct loads
545 if (Indices
.size() == 1 && Indices
.front() == 0)
547 ArgIndices
.insert(Indices
);
549 if (LoadInst
*L
= dyn_cast
<LoadInst
>(User
))
552 // Take any load, we will use it only to update Alias Analysis
553 OrigLoad
= cast
<LoadInst
>(User
->use_back());
554 OriginalLoads
[Indices
] = OrigLoad
;
557 // Add a parameter to the function for each element passed in.
558 for (ScalarizeTable::iterator SI
= ArgIndices
.begin(),
559 E
= ArgIndices
.end(); SI
!= E
; ++SI
) {
560 // not allowed to dereference ->begin() if size() is 0
561 Params
.push_back(GetElementPtrInst::getIndexedType(I
->getType(),
564 assert(Params
.back());
567 if (ArgIndices
.size() == 1 && ArgIndices
.begin()->empty())
568 ++NumArgumentsPromoted
;
570 ++NumAggregatesPromoted
;
574 // Add any function attributes.
575 if (Attributes attrs
= PAL
.getFnAttributes())
576 AttributesVec
.push_back(AttributeWithIndex::get(~0, attrs
));
578 const Type
*RetTy
= FTy
->getReturnType();
580 // Work around LLVM bug PR56: the CWriter cannot emit varargs functions which
581 // have zero fixed arguments.
582 bool ExtraArgHack
= false;
583 if (Params
.empty() && FTy
->isVarArg()) {
585 Params
.push_back(Type::getInt32Ty(F
->getContext()));
588 // Construct the new function type using the new arguments.
589 FunctionType
*NFTy
= FunctionType::get(RetTy
, Params
, FTy
->isVarArg());
591 // Create the new function body and insert it into the module.
592 Function
*NF
= Function::Create(NFTy
, F
->getLinkage(), F
->getName());
593 NF
->copyAttributesFrom(F
);
596 DEBUG(errs() << "ARG PROMOTION: Promoting to:" << *NF
<< "\n"
599 // Recompute the parameter attributes list based on the new arguments for
601 NF
->setAttributes(AttrListPtr::get(AttributesVec
.begin(),
602 AttributesVec
.end()));
603 AttributesVec
.clear();
605 F
->getParent()->getFunctionList().insert(F
, NF
);
608 // Get the alias analysis information that we need to update to reflect our
610 AliasAnalysis
&AA
= getAnalysis
<AliasAnalysis
>();
612 // Get the callgraph information that we need to update to reflect our
614 CallGraph
&CG
= getAnalysis
<CallGraph
>();
616 // Get a new callgraph node for NF.
617 CallGraphNode
*NF_CGN
= CG
.getOrInsertFunction(NF
);
620 // Loop over all of the callers of the function, transforming the call sites
621 // to pass in the loaded pointers.
623 SmallVector
<Value
*, 16> Args
;
624 while (!F
->use_empty()) {
625 CallSite CS
= CallSite::get(F
->use_back());
626 Instruction
*Call
= CS
.getInstruction();
627 const AttrListPtr
&CallPAL
= CS
.getAttributes();
629 // Add any return attributes.
630 if (Attributes attrs
= CallPAL
.getRetAttributes())
631 AttributesVec
.push_back(AttributeWithIndex::get(0, attrs
));
633 // Loop over the operands, inserting GEP and loads in the caller as
635 CallSite::arg_iterator AI
= CS
.arg_begin();
637 for (Function::arg_iterator I
= F
->arg_begin(), E
= F
->arg_end();
638 I
!= E
; ++I
, ++AI
, ++ArgIndex
)
639 if (!ArgsToPromote
.count(I
) && !ByValArgsToTransform
.count(I
)) {
640 Args
.push_back(*AI
); // Unmodified argument
642 if (Attributes Attrs
= CallPAL
.getParamAttributes(ArgIndex
))
643 AttributesVec
.push_back(AttributeWithIndex::get(Args
.size(), Attrs
));
645 } else if (ByValArgsToTransform
.count(I
)) {
646 // Emit a GEP and load for each element of the struct.
647 const Type
*AgTy
= cast
<PointerType
>(I
->getType())->getElementType();
648 const StructType
*STy
= cast
<StructType
>(AgTy
);
650 ConstantInt::get(Type::getInt32Ty(F
->getContext()), 0), 0 };
651 for (unsigned i
= 0, e
= STy
->getNumElements(); i
!= e
; ++i
) {
652 Idxs
[1] = ConstantInt::get(Type::getInt32Ty(F
->getContext()), i
);
653 Value
*Idx
= GetElementPtrInst::Create(*AI
, Idxs
, Idxs
+2,
654 (*AI
)->getName()+"."+utostr(i
),
656 // TODO: Tell AA about the new values?
657 Args
.push_back(new LoadInst(Idx
, Idx
->getName()+".val", Call
));
659 } else if (!I
->use_empty()) {
660 // Non-dead argument: insert GEPs and loads as appropriate.
661 ScalarizeTable
&ArgIndices
= ScalarizedElements
[I
];
662 // Store the Value* version of the indices in here, but declare it now
664 std::vector
<Value
*> Ops
;
665 for (ScalarizeTable::iterator SI
= ArgIndices
.begin(),
666 E
= ArgIndices
.end(); SI
!= E
; ++SI
) {
668 LoadInst
*OrigLoad
= OriginalLoads
[*SI
];
670 Ops
.reserve(SI
->size());
671 const Type
*ElTy
= V
->getType();
672 for (IndicesVector::const_iterator II
= SI
->begin(),
673 IE
= SI
->end(); II
!= IE
; ++II
) {
674 // Use i32 to index structs, and i64 for others (pointers/arrays).
675 // This satisfies GEP constraints.
676 const Type
*IdxTy
= (isa
<StructType
>(ElTy
) ?
677 Type::getInt32Ty(F
->getContext()) :
678 Type::getInt64Ty(F
->getContext()));
679 Ops
.push_back(ConstantInt::get(IdxTy
, *II
));
680 // Keep track of the type we're currently indexing
681 ElTy
= cast
<CompositeType
>(ElTy
)->getTypeAtIndex(*II
);
683 // And create a GEP to extract those indices
684 V
= GetElementPtrInst::Create(V
, Ops
.begin(), Ops
.end(),
685 V
->getName()+".idx", Call
);
687 AA
.copyValue(OrigLoad
->getOperand(0), V
);
689 Args
.push_back(new LoadInst(V
, V
->getName()+".val", Call
));
690 AA
.copyValue(OrigLoad
, Args
.back());
695 Args
.push_back(Constant::getNullValue(Type::getInt32Ty(F
->getContext())));
697 // Push any varargs arguments on the list
698 for (; AI
!= CS
.arg_end(); ++AI
, ++ArgIndex
) {
700 if (Attributes Attrs
= CallPAL
.getParamAttributes(ArgIndex
))
701 AttributesVec
.push_back(AttributeWithIndex::get(Args
.size(), Attrs
));
704 // Add any function attributes.
705 if (Attributes attrs
= CallPAL
.getFnAttributes())
706 AttributesVec
.push_back(AttributeWithIndex::get(~0, attrs
));
709 if (InvokeInst
*II
= dyn_cast
<InvokeInst
>(Call
)) {
710 New
= InvokeInst::Create(NF
, II
->getNormalDest(), II
->getUnwindDest(),
711 Args
.begin(), Args
.end(), "", Call
);
712 cast
<InvokeInst
>(New
)->setCallingConv(CS
.getCallingConv());
713 cast
<InvokeInst
>(New
)->setAttributes(AttrListPtr::get(AttributesVec
.begin(),
714 AttributesVec
.end()));
716 New
= CallInst::Create(NF
, Args
.begin(), Args
.end(), "", Call
);
717 cast
<CallInst
>(New
)->setCallingConv(CS
.getCallingConv());
718 cast
<CallInst
>(New
)->setAttributes(AttrListPtr::get(AttributesVec
.begin(),
719 AttributesVec
.end()));
720 if (cast
<CallInst
>(Call
)->isTailCall())
721 cast
<CallInst
>(New
)->setTailCall();
724 AttributesVec
.clear();
726 // Update the alias analysis implementation to know that we are replacing
727 // the old call with a new one.
728 AA
.replaceWithNewValue(Call
, New
);
730 // Update the callgraph to know that the callsite has been transformed.
731 CallGraphNode
*CalleeNode
= CG
[Call
->getParent()->getParent()];
732 CalleeNode
->replaceCallEdge(Call
, New
, NF_CGN
);
734 if (!Call
->use_empty()) {
735 Call
->replaceAllUsesWith(New
);
739 // Finally, remove the old call from the program, reducing the use-count of
741 Call
->eraseFromParent();
744 // Since we have now created the new function, splice the body of the old
745 // function right into the new function, leaving the old rotting hulk of the
747 NF
->getBasicBlockList().splice(NF
->begin(), F
->getBasicBlockList());
749 // Loop over the argument list, transfering uses of the old arguments over to
750 // the new arguments, also transfering over the names as well.
752 for (Function::arg_iterator I
= F
->arg_begin(), E
= F
->arg_end(),
753 I2
= NF
->arg_begin(); I
!= E
; ++I
) {
754 if (!ArgsToPromote
.count(I
) && !ByValArgsToTransform
.count(I
)) {
755 // If this is an unmodified argument, move the name and users over to the
757 I
->replaceAllUsesWith(I2
);
759 AA
.replaceWithNewValue(I
, I2
);
764 if (ByValArgsToTransform
.count(I
)) {
765 // In the callee, we create an alloca, and store each of the new incoming
766 // arguments into the alloca.
767 Instruction
*InsertPt
= NF
->begin()->begin();
769 // Just add all the struct element types.
770 const Type
*AgTy
= cast
<PointerType
>(I
->getType())->getElementType();
771 Value
*TheAlloca
= new AllocaInst(AgTy
, 0, "", InsertPt
);
772 const StructType
*STy
= cast
<StructType
>(AgTy
);
774 ConstantInt::get(Type::getInt32Ty(F
->getContext()), 0), 0 };
776 for (unsigned i
= 0, e
= STy
->getNumElements(); i
!= e
; ++i
) {
777 Idxs
[1] = ConstantInt::get(Type::getInt32Ty(F
->getContext()), i
);
779 GetElementPtrInst::Create(TheAlloca
, Idxs
, Idxs
+2,
780 TheAlloca
->getName()+"."+Twine(i
),
782 I2
->setName(I
->getName()+"."+Twine(i
));
783 new StoreInst(I2
++, Idx
, InsertPt
);
786 // Anything that used the arg should now use the alloca.
787 I
->replaceAllUsesWith(TheAlloca
);
788 TheAlloca
->takeName(I
);
789 AA
.replaceWithNewValue(I
, TheAlloca
);
793 if (I
->use_empty()) {
798 // Otherwise, if we promoted this argument, then all users are load
799 // instructions (or GEPs with only load users), and all loads should be
800 // using the new argument that we added.
801 ScalarizeTable
&ArgIndices
= ScalarizedElements
[I
];
803 while (!I
->use_empty()) {
804 if (LoadInst
*LI
= dyn_cast
<LoadInst
>(I
->use_back())) {
805 assert(ArgIndices
.begin()->empty() &&
806 "Load element should sort to front!");
807 I2
->setName(I
->getName()+".val");
808 LI
->replaceAllUsesWith(I2
);
809 AA
.replaceWithNewValue(LI
, I2
);
810 LI
->eraseFromParent();
811 DEBUG(errs() << "*** Promoted load of argument '" << I
->getName()
812 << "' in function '" << F
->getName() << "'\n");
814 GetElementPtrInst
*GEP
= cast
<GetElementPtrInst
>(I
->use_back());
815 IndicesVector Operands
;
816 Operands
.reserve(GEP
->getNumIndices());
817 for (User::op_iterator II
= GEP
->idx_begin(), IE
= GEP
->idx_end();
819 Operands
.push_back(cast
<ConstantInt
>(*II
)->getSExtValue());
821 // GEPs with a single 0 index can be merged with direct loads
822 if (Operands
.size() == 1 && Operands
.front() == 0)
825 Function::arg_iterator TheArg
= I2
;
826 for (ScalarizeTable::iterator It
= ArgIndices
.begin();
827 *It
!= Operands
; ++It
, ++TheArg
) {
828 assert(It
!= ArgIndices
.end() && "GEP not handled??");
831 std::string NewName
= I
->getName();
832 for (unsigned i
= 0, e
= Operands
.size(); i
!= e
; ++i
) {
833 NewName
+= "." + utostr(Operands
[i
]);
836 TheArg
->setName(NewName
);
838 DEBUG(errs() << "*** Promoted agg argument '" << TheArg
->getName()
839 << "' of function '" << NF
->getName() << "'\n");
841 // All of the uses must be load instructions. Replace them all with
842 // the argument specified by ArgNo.
843 while (!GEP
->use_empty()) {
844 LoadInst
*L
= cast
<LoadInst
>(GEP
->use_back());
845 L
->replaceAllUsesWith(TheArg
);
846 AA
.replaceWithNewValue(L
, TheArg
);
847 L
->eraseFromParent();
850 GEP
->eraseFromParent();
854 // Increment I2 past all of the arguments added for this promoted pointer.
855 for (unsigned i
= 0, e
= ArgIndices
.size(); i
!= e
; ++i
)
859 // Notify the alias analysis implementation that we inserted a new argument.
861 AA
.copyValue(Constant::getNullValue(Type::getInt32Ty(F
->getContext())),
865 // Tell the alias analysis that the old function is about to disappear.
866 AA
.replaceWithNewValue(F
, NF
);
869 NF_CGN
->stealCalledFunctionsFrom(CG
[F
]);
871 // Now that the old function is dead, delete it.
872 delete CG
.removeFunctionFromModule(F
);