1 //===- CallPromotionUtils.cpp - Utilities for call promotion ----*- C++ -*-===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 //
9 // This file implements utilities useful for promoting indirect call sites to
10 // direct call sites.
11 //
12 //===----------------------------------------------------------------------===//
13
14 #include "llvm/Transforms/Utils/CallPromotionUtils.h"
15 #include "llvm/Analysis/Loads.h"
16 #include "llvm/Analysis/TypeMetadataUtils.h"
17 #include "llvm/IR/IRBuilder.h"
18 #include "llvm/IR/Instructions.h"
19 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
20
21 using namespace llvm;
22
23 #define DEBUG_TYPE "call-promotion-utils"
24
25 /// Fix-up phi nodes in an invoke instruction's normal destination.
26 ///
27 /// After versioning an invoke instruction, values coming from the original
28 /// block will now be coming from the "merge" block. For example, in the code
29 /// below:
30 ///
31 /// then_bb:
32 /// %t0 = invoke i32 %ptr() to label %merge_bb unwind label %unwind_dst
33 ///
34 /// else_bb:
35 /// %t1 = invoke i32 %ptr() to label %merge_bb unwind label %unwind_dst
36 ///
37 /// merge_bb:
38 /// %t2 = phi i32 [ %t0, %then_bb ], [ %t1, %else_bb ]
39 /// br %normal_dst
40 ///
41 /// normal_dst:
42 /// %t3 = phi i32 [ %x, %orig_bb ], ...
43 ///
44 /// "orig_bb" is no longer a predecessor of "normal_dst", so the phi nodes in
45 /// "normal_dst" must be fixed to refer to "merge_bb":
46 ///
47 /// normal_dst:
48 /// %t3 = phi i32 [ %x, %merge_bb ], ...
49 ///
fixupPHINodeForNormalDest(InvokeInst * Invoke,BasicBlock * OrigBlock,BasicBlock * MergeBlock)50 static void fixupPHINodeForNormalDest(InvokeInst *Invoke, BasicBlock *OrigBlock,
51 BasicBlock *MergeBlock) {
52 for (PHINode &Phi : Invoke->getNormalDest()->phis()) {
53 int Idx = Phi.getBasicBlockIndex(OrigBlock);
54 if (Idx == -1)
55 continue;
56 Phi.setIncomingBlock(Idx, MergeBlock);
57 }
58 }
59
60 /// Fix-up phi nodes in an invoke instruction's unwind destination.
61 ///
62 /// After versioning an invoke instruction, values coming from the original
63 /// block will now be coming from either the "then" block or the "else" block.
64 /// For example, in the code below:
65 ///
66 /// then_bb:
67 /// %t0 = invoke i32 %ptr() to label %merge_bb unwind label %unwind_dst
68 ///
69 /// else_bb:
70 /// %t1 = invoke i32 %ptr() to label %merge_bb unwind label %unwind_dst
71 ///
72 /// unwind_dst:
73 /// %t3 = phi i32 [ %x, %orig_bb ], ...
74 ///
75 /// "orig_bb" is no longer a predecessor of "unwind_dst", so the phi nodes in
76 /// "unwind_dst" must be fixed to refer to "then_bb" and "else_bb":
77 ///
78 /// unwind_dst:
79 /// %t3 = phi i32 [ %x, %then_bb ], [ %x, %else_bb ], ...
80 ///
fixupPHINodeForUnwindDest(InvokeInst * Invoke,BasicBlock * OrigBlock,BasicBlock * ThenBlock,BasicBlock * ElseBlock)81 static void fixupPHINodeForUnwindDest(InvokeInst *Invoke, BasicBlock *OrigBlock,
82 BasicBlock *ThenBlock,
83 BasicBlock *ElseBlock) {
84 for (PHINode &Phi : Invoke->getUnwindDest()->phis()) {
85 int Idx = Phi.getBasicBlockIndex(OrigBlock);
86 if (Idx == -1)
87 continue;
88 auto *V = Phi.getIncomingValue(Idx);
89 Phi.setIncomingBlock(Idx, ThenBlock);
90 Phi.addIncoming(V, ElseBlock);
91 }
92 }
93
94 /// Create a phi node for the returned value of a call or invoke instruction.
95 ///
96 /// After versioning a call or invoke instruction that returns a value, we have
97 /// to merge the value of the original and new instructions. We do this by
98 /// creating a phi node and replacing uses of the original instruction with this
99 /// phi node.
100 ///
101 /// For example, if \p OrigInst is defined in "else_bb" and \p NewInst is
102 /// defined in "then_bb", we create the following phi node:
103 ///
104 /// ; Uses of the original instruction are replaced by uses of the phi node.
105 /// %t0 = phi i32 [ %orig_inst, %else_bb ], [ %new_inst, %then_bb ],
106 ///
createRetPHINode(Instruction * OrigInst,Instruction * NewInst,BasicBlock * MergeBlock,IRBuilder<> & Builder)107 static void createRetPHINode(Instruction *OrigInst, Instruction *NewInst,
108 BasicBlock *MergeBlock, IRBuilder<> &Builder) {
109
110 if (OrigInst->getType()->isVoidTy() || OrigInst->use_empty())
111 return;
112
113 Builder.SetInsertPoint(&MergeBlock->front());
114 PHINode *Phi = Builder.CreatePHI(OrigInst->getType(), 0);
115 SmallVector<User *, 16> UsersToUpdate(OrigInst->users());
116 for (User *U : UsersToUpdate)
117 U->replaceUsesOfWith(OrigInst, Phi);
118 Phi->addIncoming(OrigInst, OrigInst->getParent());
119 Phi->addIncoming(NewInst, NewInst->getParent());
120 }
121
122 /// Cast a call or invoke instruction to the given type.
123 ///
124 /// When promoting a call site, the return type of the call site might not match
125 /// that of the callee. If this is the case, we have to cast the returned value
126 /// to the correct type. The location of the cast depends on if we have a call
127 /// or invoke instruction.
128 ///
129 /// For example, if the call instruction below requires a bitcast after
130 /// promotion:
131 ///
132 /// orig_bb:
133 /// %t0 = call i32 @func()
134 /// ...
135 ///
136 /// The bitcast is placed after the call instruction:
137 ///
138 /// orig_bb:
139 /// ; Uses of the original return value are replaced by uses of the bitcast.
140 /// %t0 = call i32 @func()
141 /// %t1 = bitcast i32 %t0 to ...
142 /// ...
143 ///
144 /// A similar transformation is performed for invoke instructions. However,
145 /// since invokes are terminating, a new block is created for the bitcast. For
146 /// example, if the invoke instruction below requires a bitcast after promotion:
147 ///
148 /// orig_bb:
149 /// %t0 = invoke i32 @func() to label %normal_dst unwind label %unwind_dst
150 ///
151 /// The edge between the original block and the invoke's normal destination is
152 /// split, and the bitcast is placed there:
153 ///
154 /// orig_bb:
155 /// %t0 = invoke i32 @func() to label %split_bb unwind label %unwind_dst
156 ///
157 /// split_bb:
158 /// ; Uses of the original return value are replaced by uses of the bitcast.
159 /// %t1 = bitcast i32 %t0 to ...
160 /// br label %normal_dst
161 ///
createRetBitCast(CallBase & CB,Type * RetTy,CastInst ** RetBitCast)162 static void createRetBitCast(CallBase &CB, Type *RetTy, CastInst **RetBitCast) {
163
164 // Save the users of the calling instruction. These uses will be changed to
165 // use the bitcast after we create it.
166 SmallVector<User *, 16> UsersToUpdate(CB.users());
167
168 // Determine an appropriate location to create the bitcast for the return
169 // value. The location depends on if we have a call or invoke instruction.
170 Instruction *InsertBefore = nullptr;
171 if (auto *Invoke = dyn_cast<InvokeInst>(&CB))
172 InsertBefore =
173 &SplitEdge(Invoke->getParent(), Invoke->getNormalDest())->front();
174 else
175 InsertBefore = &*std::next(CB.getIterator());
176
177 // Bitcast the return value to the correct type.
178 auto *Cast = CastInst::CreateBitOrPointerCast(&CB, RetTy, "", InsertBefore);
179 if (RetBitCast)
180 *RetBitCast = Cast;
181
182 // Replace all the original uses of the calling instruction with the bitcast.
183 for (User *U : UsersToUpdate)
184 U->replaceUsesOfWith(&CB, Cast);
185 }
186
187 /// Predicate and clone the given call site.
188 ///
189 /// This function creates an if-then-else structure at the location of the call
190 /// site. The "if" condition compares the call site's called value to the given
191 /// callee. The original call site is moved into the "else" block, and a clone
192 /// of the call site is placed in the "then" block. The cloned instruction is
193 /// returned.
194 ///
195 /// For example, the call instruction below:
196 ///
197 /// orig_bb:
198 /// %t0 = call i32 %ptr()
199 /// ...
200 ///
201 /// Is replace by the following:
202 ///
203 /// orig_bb:
204 /// %cond = icmp eq i32 ()* %ptr, @func
205 /// br i1 %cond, %then_bb, %else_bb
206 ///
207 /// then_bb:
208 /// ; The clone of the original call instruction is placed in the "then"
209 /// ; block. It is not yet promoted.
210 /// %t1 = call i32 %ptr()
211 /// br merge_bb
212 ///
213 /// else_bb:
214 /// ; The original call instruction is moved to the "else" block.
215 /// %t0 = call i32 %ptr()
216 /// br merge_bb
217 ///
218 /// merge_bb:
219 /// ; Uses of the original call instruction are replaced by uses of the phi
220 /// ; node.
221 /// %t2 = phi i32 [ %t0, %else_bb ], [ %t1, %then_bb ]
222 /// ...
223 ///
224 /// A similar transformation is performed for invoke instructions. However,
225 /// since invokes are terminating, more work is required. For example, the
226 /// invoke instruction below:
227 ///
228 /// orig_bb:
229 /// %t0 = invoke %ptr() to label %normal_dst unwind label %unwind_dst
230 ///
231 /// Is replace by the following:
232 ///
233 /// orig_bb:
234 /// %cond = icmp eq i32 ()* %ptr, @func
235 /// br i1 %cond, %then_bb, %else_bb
236 ///
237 /// then_bb:
238 /// ; The clone of the original invoke instruction is placed in the "then"
239 /// ; block, and its normal destination is set to the "merge" block. It is
240 /// ; not yet promoted.
241 /// %t1 = invoke i32 %ptr() to label %merge_bb unwind label %unwind_dst
242 ///
243 /// else_bb:
244 /// ; The original invoke instruction is moved into the "else" block, and
245 /// ; its normal destination is set to the "merge" block.
246 /// %t0 = invoke i32 %ptr() to label %merge_bb unwind label %unwind_dst
247 ///
248 /// merge_bb:
249 /// ; Uses of the original invoke instruction are replaced by uses of the
250 /// ; phi node, and the merge block branches to the normal destination.
251 /// %t2 = phi i32 [ %t0, %else_bb ], [ %t1, %then_bb ]
252 /// br %normal_dst
253 ///
254 /// An indirect musttail call is processed slightly differently in that:
255 /// 1. No merge block needed for the orginal and the cloned callsite, since
256 /// either one ends the flow. No phi node is needed either.
257 /// 2. The return statement following the original call site is duplicated too
258 /// and placed immediately after the cloned call site per the IR convention.
259 ///
260 /// For example, the musttail call instruction below:
261 ///
262 /// orig_bb:
263 /// %t0 = musttail call i32 %ptr()
264 /// ...
265 ///
266 /// Is replaced by the following:
267 ///
268 /// cond_bb:
269 /// %cond = icmp eq i32 ()* %ptr, @func
270 /// br i1 %cond, %then_bb, %orig_bb
271 ///
272 /// then_bb:
273 /// ; The clone of the original call instruction is placed in the "then"
274 /// ; block. It is not yet promoted.
275 /// %t1 = musttail call i32 %ptr()
276 /// ret %t1
277 ///
278 /// orig_bb:
279 /// ; The original call instruction stays in its original block.
280 /// %t0 = musttail call i32 %ptr()
281 /// ret %t0
versionCallSite(CallBase & CB,Value * Callee,MDNode * BranchWeights)282 CallBase &llvm::versionCallSite(CallBase &CB, Value *Callee,
283 MDNode *BranchWeights) {
284
285 IRBuilder<> Builder(&CB);
286 CallBase *OrigInst = &CB;
287 BasicBlock *OrigBlock = OrigInst->getParent();
288
289 // Create the compare. The called value and callee must have the same type to
290 // be compared.
291 if (CB.getCalledOperand()->getType() != Callee->getType())
292 Callee = Builder.CreateBitCast(Callee, CB.getCalledOperand()->getType());
293 auto *Cond = Builder.CreateICmpEQ(CB.getCalledOperand(), Callee);
294
295 if (OrigInst->isMustTailCall()) {
296 // Create an if-then structure. The original instruction stays in its block,
297 // and a clone of the original instruction is placed in the "then" block.
298 Instruction *ThenTerm =
299 SplitBlockAndInsertIfThen(Cond, &CB, false, BranchWeights);
300 BasicBlock *ThenBlock = ThenTerm->getParent();
301 ThenBlock->setName("if.true.direct_targ");
302 CallBase *NewInst = cast<CallBase>(OrigInst->clone());
303 NewInst->insertBefore(ThenTerm);
304
305 // Place a clone of the optional bitcast after the new call site.
306 Value *NewRetVal = NewInst;
307 auto Next = OrigInst->getNextNode();
308 if (auto *BitCast = dyn_cast_or_null<BitCastInst>(Next)) {
309 assert(BitCast->getOperand(0) == OrigInst &&
310 "bitcast following musttail call must use the call");
311 auto NewBitCast = BitCast->clone();
312 NewBitCast->replaceUsesOfWith(OrigInst, NewInst);
313 NewBitCast->insertBefore(ThenTerm);
314 NewRetVal = NewBitCast;
315 Next = BitCast->getNextNode();
316 }
317
318 // Place a clone of the return instruction after the new call site.
319 ReturnInst *Ret = dyn_cast_or_null<ReturnInst>(Next);
320 assert(Ret && "musttail call must precede a ret with an optional bitcast");
321 auto NewRet = Ret->clone();
322 if (Ret->getReturnValue())
323 NewRet->replaceUsesOfWith(Ret->getReturnValue(), NewRetVal);
324 NewRet->insertBefore(ThenTerm);
325
326 // A return instructions is terminating, so we don't need the terminator
327 // instruction just created.
328 ThenTerm->eraseFromParent();
329
330 return *NewInst;
331 }
332
333 // Create an if-then-else structure. The original instruction is moved into
334 // the "else" block, and a clone of the original instruction is placed in the
335 // "then" block.
336 Instruction *ThenTerm = nullptr;
337 Instruction *ElseTerm = nullptr;
338 SplitBlockAndInsertIfThenElse(Cond, &CB, &ThenTerm, &ElseTerm, BranchWeights);
339 BasicBlock *ThenBlock = ThenTerm->getParent();
340 BasicBlock *ElseBlock = ElseTerm->getParent();
341 BasicBlock *MergeBlock = OrigInst->getParent();
342
343 ThenBlock->setName("if.true.direct_targ");
344 ElseBlock->setName("if.false.orig_indirect");
345 MergeBlock->setName("if.end.icp");
346
347 CallBase *NewInst = cast<CallBase>(OrigInst->clone());
348 OrigInst->moveBefore(ElseTerm);
349 NewInst->insertBefore(ThenTerm);
350
351 // If the original call site is an invoke instruction, we have extra work to
352 // do since invoke instructions are terminating. We have to fix-up phi nodes
353 // in the invoke's normal and unwind destinations.
354 if (auto *OrigInvoke = dyn_cast<InvokeInst>(OrigInst)) {
355 auto *NewInvoke = cast<InvokeInst>(NewInst);
356
357 // Invoke instructions are terminating, so we don't need the terminator
358 // instructions that were just created.
359 ThenTerm->eraseFromParent();
360 ElseTerm->eraseFromParent();
361
362 // Branch from the "merge" block to the original normal destination.
363 Builder.SetInsertPoint(MergeBlock);
364 Builder.CreateBr(OrigInvoke->getNormalDest());
365
366 // Fix-up phi nodes in the original invoke's normal and unwind destinations.
367 fixupPHINodeForNormalDest(OrigInvoke, OrigBlock, MergeBlock);
368 fixupPHINodeForUnwindDest(OrigInvoke, MergeBlock, ThenBlock, ElseBlock);
369
370 // Now set the normal destinations of the invoke instructions to be the
371 // "merge" block.
372 OrigInvoke->setNormalDest(MergeBlock);
373 NewInvoke->setNormalDest(MergeBlock);
374 }
375
376 // Create a phi node for the returned value of the call site.
377 createRetPHINode(OrigInst, NewInst, MergeBlock, Builder);
378
379 return *NewInst;
380 }
381
isLegalToPromote(const CallBase & CB,Function * Callee,const char ** FailureReason)382 bool llvm::isLegalToPromote(const CallBase &CB, Function *Callee,
383 const char **FailureReason) {
384 assert(!CB.getCalledFunction() && "Only indirect call sites can be promoted");
385
386 auto &DL = Callee->getParent()->getDataLayout();
387
388 // Check the return type. The callee's return value type must be bitcast
389 // compatible with the call site's type.
390 Type *CallRetTy = CB.getType();
391 Type *FuncRetTy = Callee->getReturnType();
392 if (CallRetTy != FuncRetTy)
393 if (!CastInst::isBitOrNoopPointerCastable(FuncRetTy, CallRetTy, DL)) {
394 if (FailureReason)
395 *FailureReason = "Return type mismatch";
396 return false;
397 }
398
399 // The number of formal arguments of the callee.
400 unsigned NumParams = Callee->getFunctionType()->getNumParams();
401
402 // The number of actual arguments in the call.
403 unsigned NumArgs = CB.arg_size();
404
405 // Check the number of arguments. The callee and call site must agree on the
406 // number of arguments.
407 if (NumArgs != NumParams && !Callee->isVarArg()) {
408 if (FailureReason)
409 *FailureReason = "The number of arguments mismatch";
410 return false;
411 }
412
413 // Check the argument types. The callee's formal argument types must be
414 // bitcast compatible with the corresponding actual argument types of the call
415 // site.
416 unsigned I = 0;
417 for (; I < NumParams; ++I) {
418 // Make sure that the callee and call agree on byval/inalloca. The types do
419 // not have to match.
420 if (Callee->hasParamAttribute(I, Attribute::ByVal) !=
421 CB.getAttributes().hasParamAttr(I, Attribute::ByVal)) {
422 if (FailureReason)
423 *FailureReason = "byval mismatch";
424 return false;
425 }
426 if (Callee->hasParamAttribute(I, Attribute::InAlloca) !=
427 CB.getAttributes().hasParamAttr(I, Attribute::InAlloca)) {
428 if (FailureReason)
429 *FailureReason = "inalloca mismatch";
430 return false;
431 }
432
433 Type *FormalTy = Callee->getFunctionType()->getFunctionParamType(I);
434 Type *ActualTy = CB.getArgOperand(I)->getType();
435 if (FormalTy == ActualTy)
436 continue;
437 if (!CastInst::isBitOrNoopPointerCastable(ActualTy, FormalTy, DL)) {
438 if (FailureReason)
439 *FailureReason = "Argument type mismatch";
440 return false;
441 }
442
443 // MustTail call needs stricter type match. See
444 // Verifier::verifyMustTailCall().
445 if (CB.isMustTailCall()) {
446 PointerType *PF = dyn_cast<PointerType>(FormalTy);
447 PointerType *PA = dyn_cast<PointerType>(ActualTy);
448 if (!PF || !PA || PF->getAddressSpace() != PA->getAddressSpace()) {
449 if (FailureReason)
450 *FailureReason = "Musttail call Argument type mismatch";
451 return false;
452 }
453 }
454 }
455 for (; I < NumArgs; I++) {
456 // Vararg functions can have more arguments than parameters.
457 assert(Callee->isVarArg());
458 if (CB.paramHasAttr(I, Attribute::StructRet)) {
459 if (FailureReason)
460 *FailureReason = "SRet arg to vararg function";
461 return false;
462 }
463 }
464
465 return true;
466 }
467
promoteCall(CallBase & CB,Function * Callee,CastInst ** RetBitCast)468 CallBase &llvm::promoteCall(CallBase &CB, Function *Callee,
469 CastInst **RetBitCast) {
470 assert(!CB.getCalledFunction() && "Only indirect call sites can be promoted");
471
472 // Set the called function of the call site to be the given callee (but don't
473 // change the type).
474 CB.setCalledOperand(Callee);
475
476 // Since the call site will no longer be direct, we must clear metadata that
477 // is only appropriate for indirect calls. This includes !prof and !callees
478 // metadata.
479 CB.setMetadata(LLVMContext::MD_prof, nullptr);
480 CB.setMetadata(LLVMContext::MD_callees, nullptr);
481
482 // If the function type of the call site matches that of the callee, no
483 // additional work is required.
484 if (CB.getFunctionType() == Callee->getFunctionType())
485 return CB;
486
487 // Save the return types of the call site and callee.
488 Type *CallSiteRetTy = CB.getType();
489 Type *CalleeRetTy = Callee->getReturnType();
490
491 // Change the function type of the call site the match that of the callee.
492 CB.mutateFunctionType(Callee->getFunctionType());
493
494 // Inspect the arguments of the call site. If an argument's type doesn't
495 // match the corresponding formal argument's type in the callee, bitcast it
496 // to the correct type.
497 auto CalleeType = Callee->getFunctionType();
498 auto CalleeParamNum = CalleeType->getNumParams();
499
500 LLVMContext &Ctx = Callee->getContext();
501 const AttributeList &CallerPAL = CB.getAttributes();
502 // The new list of argument attributes.
503 SmallVector<AttributeSet, 4> NewArgAttrs;
504 bool AttributeChanged = false;
505
506 for (unsigned ArgNo = 0; ArgNo < CalleeParamNum; ++ArgNo) {
507 auto *Arg = CB.getArgOperand(ArgNo);
508 Type *FormalTy = CalleeType->getParamType(ArgNo);
509 Type *ActualTy = Arg->getType();
510 if (FormalTy != ActualTy) {
511 auto *Cast = CastInst::CreateBitOrPointerCast(Arg, FormalTy, "", &CB);
512 CB.setArgOperand(ArgNo, Cast);
513
514 // Remove any incompatible attributes for the argument.
515 AttrBuilder ArgAttrs(Ctx, CallerPAL.getParamAttrs(ArgNo));
516 ArgAttrs.remove(AttributeFuncs::typeIncompatible(FormalTy));
517
518 // We may have a different byval/inalloca type.
519 if (ArgAttrs.getByValType())
520 ArgAttrs.addByValAttr(Callee->getParamByValType(ArgNo));
521 if (ArgAttrs.getInAllocaType())
522 ArgAttrs.addInAllocaAttr(Callee->getParamInAllocaType(ArgNo));
523
524 NewArgAttrs.push_back(AttributeSet::get(Ctx, ArgAttrs));
525 AttributeChanged = true;
526 } else
527 NewArgAttrs.push_back(CallerPAL.getParamAttrs(ArgNo));
528 }
529
530 // If the return type of the call site doesn't match that of the callee, cast
531 // the returned value to the appropriate type.
532 // Remove any incompatible return value attribute.
533 AttrBuilder RAttrs(Ctx, CallerPAL.getRetAttrs());
534 if (!CallSiteRetTy->isVoidTy() && CallSiteRetTy != CalleeRetTy) {
535 createRetBitCast(CB, CallSiteRetTy, RetBitCast);
536 RAttrs.remove(AttributeFuncs::typeIncompatible(CalleeRetTy));
537 AttributeChanged = true;
538 }
539
540 // Set the new callsite attribute.
541 if (AttributeChanged)
542 CB.setAttributes(AttributeList::get(Ctx, CallerPAL.getFnAttrs(),
543 AttributeSet::get(Ctx, RAttrs),
544 NewArgAttrs));
545
546 return CB;
547 }
548
promoteCallWithIfThenElse(CallBase & CB,Function * Callee,MDNode * BranchWeights)549 CallBase &llvm::promoteCallWithIfThenElse(CallBase &CB, Function *Callee,
550 MDNode *BranchWeights) {
551
552 // Version the indirect call site. If the called value is equal to the given
553 // callee, 'NewInst' will be executed, otherwise the original call site will
554 // be executed.
555 CallBase &NewInst = versionCallSite(CB, Callee, BranchWeights);
556
557 // Promote 'NewInst' so that it directly calls the desired function.
558 return promoteCall(NewInst, Callee);
559 }
560
tryPromoteCall(CallBase & CB)561 bool llvm::tryPromoteCall(CallBase &CB) {
562 assert(!CB.getCalledFunction());
563 Module *M = CB.getCaller()->getParent();
564 const DataLayout &DL = M->getDataLayout();
565 Value *Callee = CB.getCalledOperand();
566
567 LoadInst *VTableEntryLoad = dyn_cast<LoadInst>(Callee);
568 if (!VTableEntryLoad)
569 return false; // Not a vtable entry load.
570 Value *VTableEntryPtr = VTableEntryLoad->getPointerOperand();
571 APInt VTableOffset(DL.getTypeSizeInBits(VTableEntryPtr->getType()), 0);
572 Value *VTableBasePtr = VTableEntryPtr->stripAndAccumulateConstantOffsets(
573 DL, VTableOffset, /* AllowNonInbounds */ true);
574 LoadInst *VTablePtrLoad = dyn_cast<LoadInst>(VTableBasePtr);
575 if (!VTablePtrLoad)
576 return false; // Not a vtable load.
577 Value *Object = VTablePtrLoad->getPointerOperand();
578 APInt ObjectOffset(DL.getTypeSizeInBits(Object->getType()), 0);
579 Value *ObjectBase = Object->stripAndAccumulateConstantOffsets(
580 DL, ObjectOffset, /* AllowNonInbounds */ true);
581 if (!(isa<AllocaInst>(ObjectBase) && ObjectOffset == 0))
582 // Not an Alloca or the offset isn't zero.
583 return false;
584
585 // Look for the vtable pointer store into the object by the ctor.
586 BasicBlock::iterator BBI(VTablePtrLoad);
587 Value *VTablePtr = FindAvailableLoadedValue(
588 VTablePtrLoad, VTablePtrLoad->getParent(), BBI, 0, nullptr, nullptr);
589 if (!VTablePtr)
590 return false; // No vtable found.
591 APInt VTableOffsetGVBase(DL.getTypeSizeInBits(VTablePtr->getType()), 0);
592 Value *VTableGVBase = VTablePtr->stripAndAccumulateConstantOffsets(
593 DL, VTableOffsetGVBase, /* AllowNonInbounds */ true);
594 GlobalVariable *GV = dyn_cast<GlobalVariable>(VTableGVBase);
595 if (!(GV && GV->isConstant() && GV->hasDefinitiveInitializer()))
596 // Not in the form of a global constant variable with an initializer.
597 return false;
598
599 Constant *VTableGVInitializer = GV->getInitializer();
600 APInt VTableGVOffset = VTableOffsetGVBase + VTableOffset;
601 if (!(VTableGVOffset.getActiveBits() <= 64))
602 return false; // Out of range.
603 Constant *Ptr = getPointerAtOffset(VTableGVInitializer,
604 VTableGVOffset.getZExtValue(),
605 *M);
606 if (!Ptr)
607 return false; // No constant (function) pointer found.
608 Function *DirectCallee = dyn_cast<Function>(Ptr->stripPointerCasts());
609 if (!DirectCallee)
610 return false; // No function pointer found.
611
612 if (!isLegalToPromote(CB, DirectCallee))
613 return false;
614
615 // Success.
616 promoteCall(CB, DirectCallee);
617 return true;
618 }
619
620 #undef DEBUG_TYPE
621