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Chris Lattnerf54e7292010-01-05 05:31:55 +00001//===- InstCombinePHI.cpp -------------------------------------------------===//
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 file implements the visitPHINode function.
11//
12//===----------------------------------------------------------------------===//
13
14#include "InstCombine.h"
Duncan Sandscd6636c2010-11-14 13:30:18 +000015#include "llvm/Analysis/InstructionSimplify.h"
Chris Lattnerf54e7292010-01-05 05:31:55 +000016#include "llvm/Target/TargetData.h"
17#include "llvm/ADT/SmallPtrSet.h"
18#include "llvm/ADT/STLExtras.h"
19using namespace llvm;
20
21/// FoldPHIArgBinOpIntoPHI - If we have something like phi [add (a,b), add(a,c)]
22/// and if a/b/c and the add's all have a single use, turn this into a phi
23/// and a single binop.
24Instruction *InstCombiner::FoldPHIArgBinOpIntoPHI(PHINode &PN) {
25 Instruction *FirstInst = cast<Instruction>(PN.getIncomingValue(0));
26 assert(isa<BinaryOperator>(FirstInst) || isa<CmpInst>(FirstInst));
27 unsigned Opc = FirstInst->getOpcode();
28 Value *LHSVal = FirstInst->getOperand(0);
29 Value *RHSVal = FirstInst->getOperand(1);
30
31 const Type *LHSType = LHSVal->getType();
32 const Type *RHSType = RHSVal->getType();
33
Chris Lattnerc8cb8ef2011-02-17 23:01:49 +000034 bool isNUW = false, isNSW = false, isExact = false;
35 if (OverflowingBinaryOperator *BO =
36 dyn_cast<OverflowingBinaryOperator>(FirstInst)) {
37 isNUW = BO->hasNoUnsignedWrap();
38 isNSW = BO->hasNoSignedWrap();
39 } else if (PossiblyExactOperator *PEO =
40 dyn_cast<PossiblyExactOperator>(FirstInst))
41 isExact = PEO->isExact();
42
Chris Lattnerf54e7292010-01-05 05:31:55 +000043 // Scan to see if all operands are the same opcode, and all have one use.
44 for (unsigned i = 1; i != PN.getNumIncomingValues(); ++i) {
45 Instruction *I = dyn_cast<Instruction>(PN.getIncomingValue(i));
46 if (!I || I->getOpcode() != Opc || !I->hasOneUse() ||
47 // Verify type of the LHS matches so we don't fold cmp's of different
Chris Lattnerc8cb8ef2011-02-17 23:01:49 +000048 // types.
Chris Lattnerf54e7292010-01-05 05:31:55 +000049 I->getOperand(0)->getType() != LHSType ||
50 I->getOperand(1)->getType() != RHSType)
51 return 0;
52
53 // If they are CmpInst instructions, check their predicates
Chris Lattnerc8cb8ef2011-02-17 23:01:49 +000054 if (CmpInst *CI = dyn_cast<CmpInst>(I))
55 if (CI->getPredicate() != cast<CmpInst>(FirstInst)->getPredicate())
Chris Lattnerf54e7292010-01-05 05:31:55 +000056 return 0;
57
Chris Lattnerc8cb8ef2011-02-17 23:01:49 +000058 if (isNUW)
59 isNUW = cast<OverflowingBinaryOperator>(I)->hasNoUnsignedWrap();
60 if (isNSW)
61 isNSW = cast<OverflowingBinaryOperator>(I)->hasNoSignedWrap();
62 if (isExact)
63 isExact = cast<PossiblyExactOperator>(I)->isExact();
64
Chris Lattnerf54e7292010-01-05 05:31:55 +000065 // Keep track of which operand needs a phi node.
66 if (I->getOperand(0) != LHSVal) LHSVal = 0;
67 if (I->getOperand(1) != RHSVal) RHSVal = 0;
68 }
69
70 // If both LHS and RHS would need a PHI, don't do this transformation,
71 // because it would increase the number of PHIs entering the block,
72 // which leads to higher register pressure. This is especially
73 // bad when the PHIs are in the header of a loop.
74 if (!LHSVal && !RHSVal)
75 return 0;
76
77 // Otherwise, this is safe to transform!
78
79 Value *InLHS = FirstInst->getOperand(0);
80 Value *InRHS = FirstInst->getOperand(1);
81 PHINode *NewLHS = 0, *NewRHS = 0;
82 if (LHSVal == 0) {
Jay Foad3ecfc862011-03-30 11:28:46 +000083 NewLHS = PHINode::Create(LHSType, PN.getNumIncomingValues(),
Chris Lattnerf54e7292010-01-05 05:31:55 +000084 FirstInst->getOperand(0)->getName() + ".pn");
Chris Lattnerf54e7292010-01-05 05:31:55 +000085 NewLHS->addIncoming(InLHS, PN.getIncomingBlock(0));
86 InsertNewInstBefore(NewLHS, PN);
87 LHSVal = NewLHS;
88 }
89
90 if (RHSVal == 0) {
Jay Foad3ecfc862011-03-30 11:28:46 +000091 NewRHS = PHINode::Create(RHSType, PN.getNumIncomingValues(),
Chris Lattnerf54e7292010-01-05 05:31:55 +000092 FirstInst->getOperand(1)->getName() + ".pn");
Chris Lattnerf54e7292010-01-05 05:31:55 +000093 NewRHS->addIncoming(InRHS, PN.getIncomingBlock(0));
94 InsertNewInstBefore(NewRHS, PN);
95 RHSVal = NewRHS;
96 }
97
98 // Add all operands to the new PHIs.
99 if (NewLHS || NewRHS) {
100 for (unsigned i = 1, e = PN.getNumIncomingValues(); i != e; ++i) {
101 Instruction *InInst = cast<Instruction>(PN.getIncomingValue(i));
102 if (NewLHS) {
103 Value *NewInLHS = InInst->getOperand(0);
104 NewLHS->addIncoming(NewInLHS, PN.getIncomingBlock(i));
105 }
106 if (NewRHS) {
107 Value *NewInRHS = InInst->getOperand(1);
108 NewRHS->addIncoming(NewInRHS, PN.getIncomingBlock(i));
109 }
110 }
111 }
112
Chris Lattnerc8cb8ef2011-02-17 23:01:49 +0000113 if (CmpInst *CIOp = dyn_cast<CmpInst>(FirstInst))
114 return CmpInst::Create(CIOp->getOpcode(), CIOp->getPredicate(),
115 LHSVal, RHSVal);
116
117 BinaryOperator *BinOp = cast<BinaryOperator>(FirstInst);
118 BinaryOperator *NewBinOp =
119 BinaryOperator::Create(BinOp->getOpcode(), LHSVal, RHSVal);
120 if (isNUW) NewBinOp->setHasNoUnsignedWrap();
121 if (isNSW) NewBinOp->setHasNoSignedWrap();
122 if (isExact) NewBinOp->setIsExact();
123 return NewBinOp;
Chris Lattnerf54e7292010-01-05 05:31:55 +0000124}
125
126Instruction *InstCombiner::FoldPHIArgGEPIntoPHI(PHINode &PN) {
127 GetElementPtrInst *FirstInst =cast<GetElementPtrInst>(PN.getIncomingValue(0));
128
129 SmallVector<Value*, 16> FixedOperands(FirstInst->op_begin(),
130 FirstInst->op_end());
131 // This is true if all GEP bases are allocas and if all indices into them are
132 // constants.
133 bool AllBasePointersAreAllocas = true;
134
135 // We don't want to replace this phi if the replacement would require
136 // more than one phi, which leads to higher register pressure. This is
137 // especially bad when the PHIs are in the header of a loop.
138 bool NeededPhi = false;
139
Chris Lattner4bd82172011-02-17 22:21:26 +0000140 bool AllInBounds = true;
141
Chris Lattnerf54e7292010-01-05 05:31:55 +0000142 // Scan to see if all operands are the same opcode, and all have one use.
143 for (unsigned i = 1; i != PN.getNumIncomingValues(); ++i) {
144 GetElementPtrInst *GEP= dyn_cast<GetElementPtrInst>(PN.getIncomingValue(i));
145 if (!GEP || !GEP->hasOneUse() || GEP->getType() != FirstInst->getType() ||
146 GEP->getNumOperands() != FirstInst->getNumOperands())
147 return 0;
148
Chris Lattner4bd82172011-02-17 22:21:26 +0000149 AllInBounds &= GEP->isInBounds();
150
Chris Lattnerf54e7292010-01-05 05:31:55 +0000151 // Keep track of whether or not all GEPs are of alloca pointers.
152 if (AllBasePointersAreAllocas &&
153 (!isa<AllocaInst>(GEP->getOperand(0)) ||
154 !GEP->hasAllConstantIndices()))
155 AllBasePointersAreAllocas = false;
156
157 // Compare the operand lists.
158 for (unsigned op = 0, e = FirstInst->getNumOperands(); op != e; ++op) {
159 if (FirstInst->getOperand(op) == GEP->getOperand(op))
160 continue;
161
162 // Don't merge two GEPs when two operands differ (introducing phi nodes)
163 // if one of the PHIs has a constant for the index. The index may be
164 // substantially cheaper to compute for the constants, so making it a
165 // variable index could pessimize the path. This also handles the case
166 // for struct indices, which must always be constant.
167 if (isa<ConstantInt>(FirstInst->getOperand(op)) ||
168 isa<ConstantInt>(GEP->getOperand(op)))
169 return 0;
170
171 if (FirstInst->getOperand(op)->getType() !=GEP->getOperand(op)->getType())
172 return 0;
173
174 // If we already needed a PHI for an earlier operand, and another operand
175 // also requires a PHI, we'd be introducing more PHIs than we're
176 // eliminating, which increases register pressure on entry to the PHI's
177 // block.
178 if (NeededPhi)
179 return 0;
180
181 FixedOperands[op] = 0; // Needs a PHI.
182 NeededPhi = true;
183 }
184 }
185
186 // If all of the base pointers of the PHI'd GEPs are from allocas, don't
187 // bother doing this transformation. At best, this will just save a bit of
188 // offset calculation, but all the predecessors will have to materialize the
189 // stack address into a register anyway. We'd actually rather *clone* the
190 // load up into the predecessors so that we have a load of a gep of an alloca,
191 // which can usually all be folded into the load.
192 if (AllBasePointersAreAllocas)
193 return 0;
194
195 // Otherwise, this is safe to transform. Insert PHI nodes for each operand
196 // that is variable.
197 SmallVector<PHINode*, 16> OperandPhis(FixedOperands.size());
198
199 bool HasAnyPHIs = false;
200 for (unsigned i = 0, e = FixedOperands.size(); i != e; ++i) {
201 if (FixedOperands[i]) continue; // operand doesn't need a phi.
202 Value *FirstOp = FirstInst->getOperand(i);
Jay Foad3ecfc862011-03-30 11:28:46 +0000203 PHINode *NewPN = PHINode::Create(FirstOp->getType(), e,
Chris Lattnerf54e7292010-01-05 05:31:55 +0000204 FirstOp->getName()+".pn");
205 InsertNewInstBefore(NewPN, PN);
206
Chris Lattnerf54e7292010-01-05 05:31:55 +0000207 NewPN->addIncoming(FirstOp, PN.getIncomingBlock(0));
208 OperandPhis[i] = NewPN;
209 FixedOperands[i] = NewPN;
210 HasAnyPHIs = true;
211 }
212
213
214 // Add all operands to the new PHIs.
215 if (HasAnyPHIs) {
216 for (unsigned i = 1, e = PN.getNumIncomingValues(); i != e; ++i) {
217 GetElementPtrInst *InGEP =cast<GetElementPtrInst>(PN.getIncomingValue(i));
218 BasicBlock *InBB = PN.getIncomingBlock(i);
219
220 for (unsigned op = 0, e = OperandPhis.size(); op != e; ++op)
221 if (PHINode *OpPhi = OperandPhis[op])
222 OpPhi->addIncoming(InGEP->getOperand(op), InBB);
223 }
224 }
225
226 Value *Base = FixedOperands[0];
Chris Lattner4bd82172011-02-17 22:21:26 +0000227 GetElementPtrInst *NewGEP =
Chris Lattnerf54e7292010-01-05 05:31:55 +0000228 GetElementPtrInst::Create(Base, FixedOperands.begin()+1,
229 FixedOperands.end());
Chris Lattner1521e912011-02-17 22:32:54 +0000230 if (AllInBounds) NewGEP->setIsInBounds();
Chris Lattner4bd82172011-02-17 22:21:26 +0000231 return NewGEP;
Chris Lattnerf54e7292010-01-05 05:31:55 +0000232}
233
234
235/// isSafeAndProfitableToSinkLoad - Return true if we know that it is safe to
236/// sink the load out of the block that defines it. This means that it must be
237/// obvious the value of the load is not changed from the point of the load to
238/// the end of the block it is in.
239///
240/// Finally, it is safe, but not profitable, to sink a load targetting a
241/// non-address-taken alloca. Doing so will cause us to not promote the alloca
242/// to a register.
243static bool isSafeAndProfitableToSinkLoad(LoadInst *L) {
244 BasicBlock::iterator BBI = L, E = L->getParent()->end();
245
246 for (++BBI; BBI != E; ++BBI)
247 if (BBI->mayWriteToMemory())
248 return false;
249
250 // Check for non-address taken alloca. If not address-taken already, it isn't
251 // profitable to do this xform.
252 if (AllocaInst *AI = dyn_cast<AllocaInst>(L->getOperand(0))) {
253 bool isAddressTaken = false;
254 for (Value::use_iterator UI = AI->use_begin(), E = AI->use_end();
255 UI != E; ++UI) {
Gabor Greif40119ce2010-07-12 14:15:58 +0000256 User *U = *UI;
257 if (isa<LoadInst>(U)) continue;
258 if (StoreInst *SI = dyn_cast<StoreInst>(U)) {
Chris Lattnerf54e7292010-01-05 05:31:55 +0000259 // If storing TO the alloca, then the address isn't taken.
260 if (SI->getOperand(1) == AI) continue;
261 }
262 isAddressTaken = true;
263 break;
264 }
265
266 if (!isAddressTaken && AI->isStaticAlloca())
267 return false;
268 }
269
270 // If this load is a load from a GEP with a constant offset from an alloca,
271 // then we don't want to sink it. In its present form, it will be
272 // load [constant stack offset]. Sinking it will cause us to have to
273 // materialize the stack addresses in each predecessor in a register only to
274 // do a shared load from register in the successor.
275 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(L->getOperand(0)))
276 if (AllocaInst *AI = dyn_cast<AllocaInst>(GEP->getOperand(0)))
277 if (AI->isStaticAlloca() && GEP->hasAllConstantIndices())
278 return false;
279
280 return true;
281}
282
283Instruction *InstCombiner::FoldPHIArgLoadIntoPHI(PHINode &PN) {
284 LoadInst *FirstLI = cast<LoadInst>(PN.getIncomingValue(0));
285
286 // When processing loads, we need to propagate two bits of information to the
287 // sunk load: whether it is volatile, and what its alignment is. We currently
288 // don't sink loads when some have their alignment specified and some don't.
289 // visitLoadInst will propagate an alignment onto the load when TD is around,
290 // and if TD isn't around, we can't handle the mixed case.
291 bool isVolatile = FirstLI->isVolatile();
292 unsigned LoadAlignment = FirstLI->getAlignment();
Chris Lattner4c5fb1a2010-03-05 18:53:28 +0000293 unsigned LoadAddrSpace = FirstLI->getPointerAddressSpace();
Chris Lattnerf54e7292010-01-05 05:31:55 +0000294
295 // We can't sink the load if the loaded value could be modified between the
296 // load and the PHI.
297 if (FirstLI->getParent() != PN.getIncomingBlock(0) ||
298 !isSafeAndProfitableToSinkLoad(FirstLI))
299 return 0;
300
301 // If the PHI is of volatile loads and the load block has multiple
302 // successors, sinking it would remove a load of the volatile value from
303 // the path through the other successor.
304 if (isVolatile &&
305 FirstLI->getParent()->getTerminator()->getNumSuccessors() != 1)
306 return 0;
307
308 // Check to see if all arguments are the same operation.
309 for (unsigned i = 1, e = PN.getNumIncomingValues(); i != e; ++i) {
310 LoadInst *LI = dyn_cast<LoadInst>(PN.getIncomingValue(i));
311 if (!LI || !LI->hasOneUse())
312 return 0;
313
314 // We can't sink the load if the loaded value could be modified between
315 // the load and the PHI.
316 if (LI->isVolatile() != isVolatile ||
317 LI->getParent() != PN.getIncomingBlock(i) ||
Chris Lattner4c5fb1a2010-03-05 18:53:28 +0000318 LI->getPointerAddressSpace() != LoadAddrSpace ||
Chris Lattnerf54e7292010-01-05 05:31:55 +0000319 !isSafeAndProfitableToSinkLoad(LI))
320 return 0;
321
322 // If some of the loads have an alignment specified but not all of them,
323 // we can't do the transformation.
324 if ((LoadAlignment != 0) != (LI->getAlignment() != 0))
325 return 0;
326
327 LoadAlignment = std::min(LoadAlignment, LI->getAlignment());
328
329 // If the PHI is of volatile loads and the load block has multiple
330 // successors, sinking it would remove a load of the volatile value from
331 // the path through the other successor.
332 if (isVolatile &&
333 LI->getParent()->getTerminator()->getNumSuccessors() != 1)
334 return 0;
335 }
336
337 // Okay, they are all the same operation. Create a new PHI node of the
338 // correct type, and PHI together all of the LHS's of the instructions.
339 PHINode *NewPN = PHINode::Create(FirstLI->getOperand(0)->getType(),
Jay Foad3ecfc862011-03-30 11:28:46 +0000340 PN.getNumIncomingValues(),
Chris Lattnerf54e7292010-01-05 05:31:55 +0000341 PN.getName()+".in");
Chris Lattnerf54e7292010-01-05 05:31:55 +0000342
343 Value *InVal = FirstLI->getOperand(0);
344 NewPN->addIncoming(InVal, PN.getIncomingBlock(0));
345
346 // Add all operands to the new PHI.
347 for (unsigned i = 1, e = PN.getNumIncomingValues(); i != e; ++i) {
348 Value *NewInVal = cast<LoadInst>(PN.getIncomingValue(i))->getOperand(0);
349 if (NewInVal != InVal)
350 InVal = 0;
351 NewPN->addIncoming(NewInVal, PN.getIncomingBlock(i));
352 }
353
354 Value *PhiVal;
355 if (InVal) {
356 // The new PHI unions all of the same values together. This is really
357 // common, so we handle it intelligently here for compile-time speed.
358 PhiVal = InVal;
359 delete NewPN;
360 } else {
361 InsertNewInstBefore(NewPN, PN);
362 PhiVal = NewPN;
363 }
364
365 // If this was a volatile load that we are merging, make sure to loop through
366 // and mark all the input loads as non-volatile. If we don't do this, we will
367 // insert a new volatile load and the old ones will not be deletable.
368 if (isVolatile)
369 for (unsigned i = 0, e = PN.getNumIncomingValues(); i != e; ++i)
370 cast<LoadInst>(PN.getIncomingValue(i))->setVolatile(false);
371
372 return new LoadInst(PhiVal, "", isVolatile, LoadAlignment);
373}
374
375
376
377/// FoldPHIArgOpIntoPHI - If all operands to a PHI node are the same "unary"
378/// operator and they all are only used by the PHI, PHI together their
379/// inputs, and do the operation once, to the result of the PHI.
380Instruction *InstCombiner::FoldPHIArgOpIntoPHI(PHINode &PN) {
381 Instruction *FirstInst = cast<Instruction>(PN.getIncomingValue(0));
382
383 if (isa<GetElementPtrInst>(FirstInst))
384 return FoldPHIArgGEPIntoPHI(PN);
385 if (isa<LoadInst>(FirstInst))
386 return FoldPHIArgLoadIntoPHI(PN);
387
388 // Scan the instruction, looking for input operations that can be folded away.
389 // If all input operands to the phi are the same instruction (e.g. a cast from
390 // the same type or "+42") we can pull the operation through the PHI, reducing
391 // code size and simplifying code.
392 Constant *ConstantOp = 0;
393 const Type *CastSrcTy = 0;
Chris Lattnerc8cb8ef2011-02-17 23:01:49 +0000394 bool isNUW = false, isNSW = false, isExact = false;
Chris Lattnerf54e7292010-01-05 05:31:55 +0000395
396 if (isa<CastInst>(FirstInst)) {
397 CastSrcTy = FirstInst->getOperand(0)->getType();
398
399 // Be careful about transforming integer PHIs. We don't want to pessimize
400 // the code by turning an i32 into an i1293.
Duncan Sands1df98592010-02-16 11:11:14 +0000401 if (PN.getType()->isIntegerTy() && CastSrcTy->isIntegerTy()) {
Chris Lattnerf54e7292010-01-05 05:31:55 +0000402 if (!ShouldChangeType(PN.getType(), CastSrcTy))
403 return 0;
404 }
405 } else if (isa<BinaryOperator>(FirstInst) || isa<CmpInst>(FirstInst)) {
406 // Can fold binop, compare or shift here if the RHS is a constant,
407 // otherwise call FoldPHIArgBinOpIntoPHI.
408 ConstantOp = dyn_cast<Constant>(FirstInst->getOperand(1));
409 if (ConstantOp == 0)
410 return FoldPHIArgBinOpIntoPHI(PN);
Chris Lattnerc8cb8ef2011-02-17 23:01:49 +0000411
412 if (OverflowingBinaryOperator *BO =
413 dyn_cast<OverflowingBinaryOperator>(FirstInst)) {
414 isNUW = BO->hasNoUnsignedWrap();
415 isNSW = BO->hasNoSignedWrap();
416 } else if (PossiblyExactOperator *PEO =
417 dyn_cast<PossiblyExactOperator>(FirstInst))
418 isExact = PEO->isExact();
Chris Lattnerf54e7292010-01-05 05:31:55 +0000419 } else {
420 return 0; // Cannot fold this operation.
421 }
422
423 // Check to see if all arguments are the same operation.
424 for (unsigned i = 1, e = PN.getNumIncomingValues(); i != e; ++i) {
425 Instruction *I = dyn_cast<Instruction>(PN.getIncomingValue(i));
426 if (I == 0 || !I->hasOneUse() || !I->isSameOperationAs(FirstInst))
427 return 0;
428 if (CastSrcTy) {
429 if (I->getOperand(0)->getType() != CastSrcTy)
430 return 0; // Cast operation must match.
431 } else if (I->getOperand(1) != ConstantOp) {
432 return 0;
433 }
Chris Lattnerc8cb8ef2011-02-17 23:01:49 +0000434
435 if (isNUW)
436 isNUW = cast<OverflowingBinaryOperator>(I)->hasNoUnsignedWrap();
437 if (isNSW)
438 isNSW = cast<OverflowingBinaryOperator>(I)->hasNoSignedWrap();
439 if (isExact)
440 isExact = cast<PossiblyExactOperator>(I)->isExact();
Chris Lattnerf54e7292010-01-05 05:31:55 +0000441 }
442
443 // Okay, they are all the same operation. Create a new PHI node of the
444 // correct type, and PHI together all of the LHS's of the instructions.
445 PHINode *NewPN = PHINode::Create(FirstInst->getOperand(0)->getType(),
Jay Foad3ecfc862011-03-30 11:28:46 +0000446 PN.getNumIncomingValues(),
Chris Lattnerf54e7292010-01-05 05:31:55 +0000447 PN.getName()+".in");
Chris Lattnerf54e7292010-01-05 05:31:55 +0000448
449 Value *InVal = FirstInst->getOperand(0);
450 NewPN->addIncoming(InVal, PN.getIncomingBlock(0));
451
452 // Add all operands to the new PHI.
453 for (unsigned i = 1, e = PN.getNumIncomingValues(); i != e; ++i) {
454 Value *NewInVal = cast<Instruction>(PN.getIncomingValue(i))->getOperand(0);
455 if (NewInVal != InVal)
456 InVal = 0;
457 NewPN->addIncoming(NewInVal, PN.getIncomingBlock(i));
458 }
459
460 Value *PhiVal;
461 if (InVal) {
462 // The new PHI unions all of the same values together. This is really
463 // common, so we handle it intelligently here for compile-time speed.
464 PhiVal = InVal;
465 delete NewPN;
466 } else {
467 InsertNewInstBefore(NewPN, PN);
468 PhiVal = NewPN;
469 }
470
471 // Insert and return the new operation.
472 if (CastInst *FirstCI = dyn_cast<CastInst>(FirstInst))
473 return CastInst::Create(FirstCI->getOpcode(), PhiVal, PN.getType());
474
Chris Lattnerc8cb8ef2011-02-17 23:01:49 +0000475 if (BinaryOperator *BinOp = dyn_cast<BinaryOperator>(FirstInst)) {
476 BinOp = BinaryOperator::Create(BinOp->getOpcode(), PhiVal, ConstantOp);
477 if (isNUW) BinOp->setHasNoUnsignedWrap();
478 if (isNSW) BinOp->setHasNoSignedWrap();
479 if (isExact) BinOp->setIsExact();
480 return BinOp;
481 }
Chris Lattnerf54e7292010-01-05 05:31:55 +0000482
483 CmpInst *CIOp = cast<CmpInst>(FirstInst);
484 return CmpInst::Create(CIOp->getOpcode(), CIOp->getPredicate(),
485 PhiVal, ConstantOp);
486}
487
488/// DeadPHICycle - Return true if this PHI node is only used by a PHI node cycle
489/// that is dead.
490static bool DeadPHICycle(PHINode *PN,
491 SmallPtrSet<PHINode*, 16> &PotentiallyDeadPHIs) {
492 if (PN->use_empty()) return true;
493 if (!PN->hasOneUse()) return false;
494
495 // Remember this node, and if we find the cycle, return.
496 if (!PotentiallyDeadPHIs.insert(PN))
497 return true;
498
499 // Don't scan crazily complex things.
500 if (PotentiallyDeadPHIs.size() == 16)
501 return false;
502
503 if (PHINode *PU = dyn_cast<PHINode>(PN->use_back()))
504 return DeadPHICycle(PU, PotentiallyDeadPHIs);
505
506 return false;
507}
508
509/// PHIsEqualValue - Return true if this phi node is always equal to
510/// NonPhiInVal. This happens with mutually cyclic phi nodes like:
511/// z = some value; x = phi (y, z); y = phi (x, z)
512static bool PHIsEqualValue(PHINode *PN, Value *NonPhiInVal,
513 SmallPtrSet<PHINode*, 16> &ValueEqualPHIs) {
514 // See if we already saw this PHI node.
515 if (!ValueEqualPHIs.insert(PN))
516 return true;
517
518 // Don't scan crazily complex things.
519 if (ValueEqualPHIs.size() == 16)
520 return false;
521
522 // Scan the operands to see if they are either phi nodes or are equal to
523 // the value.
524 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
525 Value *Op = PN->getIncomingValue(i);
526 if (PHINode *OpPN = dyn_cast<PHINode>(Op)) {
527 if (!PHIsEqualValue(OpPN, NonPhiInVal, ValueEqualPHIs))
528 return false;
529 } else if (Op != NonPhiInVal)
530 return false;
531 }
532
533 return true;
534}
535
536
537namespace {
538struct PHIUsageRecord {
539 unsigned PHIId; // The ID # of the PHI (something determinstic to sort on)
540 unsigned Shift; // The amount shifted.
541 Instruction *Inst; // The trunc instruction.
542
543 PHIUsageRecord(unsigned pn, unsigned Sh, Instruction *User)
544 : PHIId(pn), Shift(Sh), Inst(User) {}
545
546 bool operator<(const PHIUsageRecord &RHS) const {
547 if (PHIId < RHS.PHIId) return true;
548 if (PHIId > RHS.PHIId) return false;
549 if (Shift < RHS.Shift) return true;
550 if (Shift > RHS.Shift) return false;
551 return Inst->getType()->getPrimitiveSizeInBits() <
552 RHS.Inst->getType()->getPrimitiveSizeInBits();
553 }
554};
555
556struct LoweredPHIRecord {
557 PHINode *PN; // The PHI that was lowered.
558 unsigned Shift; // The amount shifted.
559 unsigned Width; // The width extracted.
560
561 LoweredPHIRecord(PHINode *pn, unsigned Sh, const Type *Ty)
562 : PN(pn), Shift(Sh), Width(Ty->getPrimitiveSizeInBits()) {}
563
564 // Ctor form used by DenseMap.
565 LoweredPHIRecord(PHINode *pn, unsigned Sh)
566 : PN(pn), Shift(Sh), Width(0) {}
567};
568}
569
570namespace llvm {
571 template<>
572 struct DenseMapInfo<LoweredPHIRecord> {
573 static inline LoweredPHIRecord getEmptyKey() {
574 return LoweredPHIRecord(0, 0);
575 }
576 static inline LoweredPHIRecord getTombstoneKey() {
577 return LoweredPHIRecord(0, 1);
578 }
579 static unsigned getHashValue(const LoweredPHIRecord &Val) {
580 return DenseMapInfo<PHINode*>::getHashValue(Val.PN) ^ (Val.Shift>>3) ^
581 (Val.Width>>3);
582 }
583 static bool isEqual(const LoweredPHIRecord &LHS,
584 const LoweredPHIRecord &RHS) {
585 return LHS.PN == RHS.PN && LHS.Shift == RHS.Shift &&
586 LHS.Width == RHS.Width;
587 }
588 };
589 template <>
590 struct isPodLike<LoweredPHIRecord> { static const bool value = true; };
591}
592
593
594/// SliceUpIllegalIntegerPHI - This is an integer PHI and we know that it has an
595/// illegal type: see if it is only used by trunc or trunc(lshr) operations. If
596/// so, we split the PHI into the various pieces being extracted. This sort of
597/// thing is introduced when SROA promotes an aggregate to large integer values.
598///
599/// TODO: The user of the trunc may be an bitcast to float/double/vector or an
600/// inttoptr. We should produce new PHIs in the right type.
601///
602Instruction *InstCombiner::SliceUpIllegalIntegerPHI(PHINode &FirstPhi) {
603 // PHIUsers - Keep track of all of the truncated values extracted from a set
604 // of PHIs, along with their offset. These are the things we want to rewrite.
605 SmallVector<PHIUsageRecord, 16> PHIUsers;
606
607 // PHIs are often mutually cyclic, so we keep track of a whole set of PHI
608 // nodes which are extracted from. PHIsToSlice is a set we use to avoid
609 // revisiting PHIs, PHIsInspected is a ordered list of PHIs that we need to
610 // check the uses of (to ensure they are all extracts).
611 SmallVector<PHINode*, 8> PHIsToSlice;
612 SmallPtrSet<PHINode*, 8> PHIsInspected;
613
614 PHIsToSlice.push_back(&FirstPhi);
615 PHIsInspected.insert(&FirstPhi);
616
617 for (unsigned PHIId = 0; PHIId != PHIsToSlice.size(); ++PHIId) {
618 PHINode *PN = PHIsToSlice[PHIId];
619
620 // Scan the input list of the PHI. If any input is an invoke, and if the
621 // input is defined in the predecessor, then we won't be split the critical
622 // edge which is required to insert a truncate. Because of this, we have to
623 // bail out.
624 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
625 InvokeInst *II = dyn_cast<InvokeInst>(PN->getIncomingValue(i));
626 if (II == 0) continue;
627 if (II->getParent() != PN->getIncomingBlock(i))
628 continue;
629
630 // If we have a phi, and if it's directly in the predecessor, then we have
631 // a critical edge where we need to put the truncate. Since we can't
632 // split the edge in instcombine, we have to bail out.
633 return 0;
634 }
635
636
637 for (Value::use_iterator UI = PN->use_begin(), E = PN->use_end();
638 UI != E; ++UI) {
639 Instruction *User = cast<Instruction>(*UI);
640
641 // If the user is a PHI, inspect its uses recursively.
642 if (PHINode *UserPN = dyn_cast<PHINode>(User)) {
643 if (PHIsInspected.insert(UserPN))
644 PHIsToSlice.push_back(UserPN);
645 continue;
646 }
647
648 // Truncates are always ok.
649 if (isa<TruncInst>(User)) {
650 PHIUsers.push_back(PHIUsageRecord(PHIId, 0, User));
651 continue;
652 }
653
654 // Otherwise it must be a lshr which can only be used by one trunc.
655 if (User->getOpcode() != Instruction::LShr ||
656 !User->hasOneUse() || !isa<TruncInst>(User->use_back()) ||
657 !isa<ConstantInt>(User->getOperand(1)))
658 return 0;
659
660 unsigned Shift = cast<ConstantInt>(User->getOperand(1))->getZExtValue();
661 PHIUsers.push_back(PHIUsageRecord(PHIId, Shift, User->use_back()));
662 }
663 }
664
665 // If we have no users, they must be all self uses, just nuke the PHI.
666 if (PHIUsers.empty())
667 return ReplaceInstUsesWith(FirstPhi, UndefValue::get(FirstPhi.getType()));
668
669 // If this phi node is transformable, create new PHIs for all the pieces
670 // extracted out of it. First, sort the users by their offset and size.
671 array_pod_sort(PHIUsers.begin(), PHIUsers.end());
672
673 DEBUG(errs() << "SLICING UP PHI: " << FirstPhi << '\n';
674 for (unsigned i = 1, e = PHIsToSlice.size(); i != e; ++i)
675 errs() << "AND USER PHI #" << i << ": " << *PHIsToSlice[i] <<'\n';
676 );
677
678 // PredValues - This is a temporary used when rewriting PHI nodes. It is
679 // hoisted out here to avoid construction/destruction thrashing.
680 DenseMap<BasicBlock*, Value*> PredValues;
681
682 // ExtractedVals - Each new PHI we introduce is saved here so we don't
683 // introduce redundant PHIs.
684 DenseMap<LoweredPHIRecord, PHINode*> ExtractedVals;
685
686 for (unsigned UserI = 0, UserE = PHIUsers.size(); UserI != UserE; ++UserI) {
687 unsigned PHIId = PHIUsers[UserI].PHIId;
688 PHINode *PN = PHIsToSlice[PHIId];
689 unsigned Offset = PHIUsers[UserI].Shift;
690 const Type *Ty = PHIUsers[UserI].Inst->getType();
691
692 PHINode *EltPHI;
693
694 // If we've already lowered a user like this, reuse the previously lowered
695 // value.
696 if ((EltPHI = ExtractedVals[LoweredPHIRecord(PN, Offset, Ty)]) == 0) {
697
698 // Otherwise, Create the new PHI node for this user.
Jay Foad3ecfc862011-03-30 11:28:46 +0000699 EltPHI = PHINode::Create(Ty, PN->getNumIncomingValues(),
700 PN->getName()+".off"+Twine(Offset), PN);
Chris Lattnerf54e7292010-01-05 05:31:55 +0000701 assert(EltPHI->getType() != PN->getType() &&
702 "Truncate didn't shrink phi?");
703
704 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
705 BasicBlock *Pred = PN->getIncomingBlock(i);
706 Value *&PredVal = PredValues[Pred];
707
708 // If we already have a value for this predecessor, reuse it.
709 if (PredVal) {
710 EltPHI->addIncoming(PredVal, Pred);
711 continue;
712 }
713
714 // Handle the PHI self-reuse case.
715 Value *InVal = PN->getIncomingValue(i);
716 if (InVal == PN) {
717 PredVal = EltPHI;
718 EltPHI->addIncoming(PredVal, Pred);
719 continue;
720 }
721
722 if (PHINode *InPHI = dyn_cast<PHINode>(PN)) {
723 // If the incoming value was a PHI, and if it was one of the PHIs we
724 // already rewrote it, just use the lowered value.
725 if (Value *Res = ExtractedVals[LoweredPHIRecord(InPHI, Offset, Ty)]) {
726 PredVal = Res;
727 EltPHI->addIncoming(PredVal, Pred);
728 continue;
729 }
730 }
731
732 // Otherwise, do an extract in the predecessor.
733 Builder->SetInsertPoint(Pred, Pred->getTerminator());
734 Value *Res = InVal;
735 if (Offset)
736 Res = Builder->CreateLShr(Res, ConstantInt::get(InVal->getType(),
737 Offset), "extract");
738 Res = Builder->CreateTrunc(Res, Ty, "extract.t");
739 PredVal = Res;
740 EltPHI->addIncoming(Res, Pred);
741
742 // If the incoming value was a PHI, and if it was one of the PHIs we are
743 // rewriting, we will ultimately delete the code we inserted. This
744 // means we need to revisit that PHI to make sure we extract out the
745 // needed piece.
746 if (PHINode *OldInVal = dyn_cast<PHINode>(PN->getIncomingValue(i)))
747 if (PHIsInspected.count(OldInVal)) {
748 unsigned RefPHIId = std::find(PHIsToSlice.begin(),PHIsToSlice.end(),
749 OldInVal)-PHIsToSlice.begin();
750 PHIUsers.push_back(PHIUsageRecord(RefPHIId, Offset,
751 cast<Instruction>(Res)));
752 ++UserE;
753 }
754 }
755 PredValues.clear();
756
757 DEBUG(errs() << " Made element PHI for offset " << Offset << ": "
758 << *EltPHI << '\n');
759 ExtractedVals[LoweredPHIRecord(PN, Offset, Ty)] = EltPHI;
760 }
761
762 // Replace the use of this piece with the PHI node.
763 ReplaceInstUsesWith(*PHIUsers[UserI].Inst, EltPHI);
764 }
765
766 // Replace all the remaining uses of the PHI nodes (self uses and the lshrs)
767 // with undefs.
768 Value *Undef = UndefValue::get(FirstPhi.getType());
769 for (unsigned i = 1, e = PHIsToSlice.size(); i != e; ++i)
770 ReplaceInstUsesWith(*PHIsToSlice[i], Undef);
771 return ReplaceInstUsesWith(FirstPhi, Undef);
772}
773
774// PHINode simplification
775//
776Instruction *InstCombiner::visitPHINode(PHINode &PN) {
777 // If LCSSA is around, don't mess with Phi nodes
778 if (MustPreserveLCSSA) return 0;
Duncan Sandscd6636c2010-11-14 13:30:18 +0000779
780 if (Value *V = SimplifyInstruction(&PN, TD))
Chris Lattnerf54e7292010-01-05 05:31:55 +0000781 return ReplaceInstUsesWith(PN, V);
782
783 // If all PHI operands are the same operation, pull them through the PHI,
784 // reducing code size.
785 if (isa<Instruction>(PN.getIncomingValue(0)) &&
786 isa<Instruction>(PN.getIncomingValue(1)) &&
787 cast<Instruction>(PN.getIncomingValue(0))->getOpcode() ==
788 cast<Instruction>(PN.getIncomingValue(1))->getOpcode() &&
789 // FIXME: The hasOneUse check will fail for PHIs that use the value more
790 // than themselves more than once.
791 PN.getIncomingValue(0)->hasOneUse())
792 if (Instruction *Result = FoldPHIArgOpIntoPHI(PN))
793 return Result;
794
795 // If this is a trivial cycle in the PHI node graph, remove it. Basically, if
796 // this PHI only has a single use (a PHI), and if that PHI only has one use (a
797 // PHI)... break the cycle.
798 if (PN.hasOneUse()) {
799 Instruction *PHIUser = cast<Instruction>(PN.use_back());
800 if (PHINode *PU = dyn_cast<PHINode>(PHIUser)) {
801 SmallPtrSet<PHINode*, 16> PotentiallyDeadPHIs;
802 PotentiallyDeadPHIs.insert(&PN);
803 if (DeadPHICycle(PU, PotentiallyDeadPHIs))
804 return ReplaceInstUsesWith(PN, UndefValue::get(PN.getType()));
805 }
806
807 // If this phi has a single use, and if that use just computes a value for
808 // the next iteration of a loop, delete the phi. This occurs with unused
809 // induction variables, e.g. "for (int j = 0; ; ++j);". Detecting this
810 // common case here is good because the only other things that catch this
811 // are induction variable analysis (sometimes) and ADCE, which is only run
812 // late.
813 if (PHIUser->hasOneUse() &&
814 (isa<BinaryOperator>(PHIUser) || isa<GetElementPtrInst>(PHIUser)) &&
815 PHIUser->use_back() == &PN) {
816 return ReplaceInstUsesWith(PN, UndefValue::get(PN.getType()));
817 }
818 }
819
820 // We sometimes end up with phi cycles that non-obviously end up being the
821 // same value, for example:
822 // z = some value; x = phi (y, z); y = phi (x, z)
823 // where the phi nodes don't necessarily need to be in the same block. Do a
824 // quick check to see if the PHI node only contains a single non-phi value, if
825 // so, scan to see if the phi cycle is actually equal to that value.
826 {
827 unsigned InValNo = 0, NumOperandVals = PN.getNumIncomingValues();
828 // Scan for the first non-phi operand.
829 while (InValNo != NumOperandVals &&
830 isa<PHINode>(PN.getIncomingValue(InValNo)))
831 ++InValNo;
832
833 if (InValNo != NumOperandVals) {
834 Value *NonPhiInVal = PN.getOperand(InValNo);
835
836 // Scan the rest of the operands to see if there are any conflicts, if so
837 // there is no need to recursively scan other phis.
838 for (++InValNo; InValNo != NumOperandVals; ++InValNo) {
839 Value *OpVal = PN.getIncomingValue(InValNo);
840 if (OpVal != NonPhiInVal && !isa<PHINode>(OpVal))
841 break;
842 }
843
844 // If we scanned over all operands, then we have one unique value plus
845 // phi values. Scan PHI nodes to see if they all merge in each other or
846 // the value.
847 if (InValNo == NumOperandVals) {
848 SmallPtrSet<PHINode*, 16> ValueEqualPHIs;
849 if (PHIsEqualValue(&PN, NonPhiInVal, ValueEqualPHIs))
850 return ReplaceInstUsesWith(PN, NonPhiInVal);
851 }
852 }
853 }
854
855 // If there are multiple PHIs, sort their operands so that they all list
856 // the blocks in the same order. This will help identical PHIs be eliminated
857 // by other passes. Other passes shouldn't depend on this for correctness
858 // however.
859 PHINode *FirstPN = cast<PHINode>(PN.getParent()->begin());
860 if (&PN != FirstPN)
861 for (unsigned i = 0, e = FirstPN->getNumIncomingValues(); i != e; ++i) {
862 BasicBlock *BBA = PN.getIncomingBlock(i);
863 BasicBlock *BBB = FirstPN->getIncomingBlock(i);
864 if (BBA != BBB) {
865 Value *VA = PN.getIncomingValue(i);
866 unsigned j = PN.getBasicBlockIndex(BBB);
867 Value *VB = PN.getIncomingValue(j);
868 PN.setIncomingBlock(i, BBB);
869 PN.setIncomingValue(i, VB);
870 PN.setIncomingBlock(j, BBA);
871 PN.setIncomingValue(j, VA);
872 // NOTE: Instcombine normally would want us to "return &PN" if we
873 // modified any of the operands of an instruction. However, since we
874 // aren't adding or removing uses (just rearranging them) we don't do
875 // this in this case.
876 }
877 }
878
879 // If this is an integer PHI and we know that it has an illegal type, see if
880 // it is only used by trunc or trunc(lshr) operations. If so, we split the
881 // PHI into the various pieces being extracted. This sort of thing is
882 // introduced when SROA promotes an aggregate to a single large integer type.
Duncan Sands1df98592010-02-16 11:11:14 +0000883 if (PN.getType()->isIntegerTy() && TD &&
Chris Lattnerf54e7292010-01-05 05:31:55 +0000884 !TD->isLegalInteger(PN.getType()->getPrimitiveSizeInBits()))
885 if (Instruction *Res = SliceUpIllegalIntegerPHI(PN))
886 return Res;
887
888 return 0;
Benjamin Kramereade0022010-01-05 13:32:48 +0000889}