1#include "llvm/Transforms/Utils/VNCoercion.h"
2#include "llvm/Analysis/ConstantFolding.h"
3#include "llvm/Analysis/ValueTracking.h"
4#include "llvm/IR/IRBuilder.h"
5#include "llvm/IR/IntrinsicInst.h"
6
7#define DEBUG_TYPE "vncoerce"
8
9namespace llvm {
10namespace VNCoercion {
11
12static bool isFirstClassAggregateOrScalableType(Type *Ty) {
13 return Ty->isStructTy() || Ty->isArrayTy() || isa<ScalableVectorType>(Val: Ty);
14}
15
16/// Return true if coerceAvailableValueToLoadType will succeed.
17bool canCoerceMustAliasedValueToLoad(Value *StoredVal, Type *LoadTy,
18 Function *F) {
19 Type *StoredTy = StoredVal->getType();
20 if (StoredTy == LoadTy)
21 return true;
22
23 const DataLayout &DL = F->getDataLayout();
24 TypeSize MinStoreSize = DL.getTypeSizeInBits(Ty: StoredTy);
25 TypeSize LoadSize = DL.getTypeSizeInBits(Ty: LoadTy);
26 if (isa<ScalableVectorType>(Val: StoredTy) && isa<ScalableVectorType>(Val: LoadTy) &&
27 MinStoreSize == LoadSize)
28 return true;
29
30 // If the loaded/stored value is a first class array/struct, don't try to
31 // transform them. We need to be able to bitcast to integer. For scalable
32 // vectors forwarded to fixed-sized vectors @llvm.vector.extract is used.
33 if (isa<ScalableVectorType>(Val: StoredTy) && isa<FixedVectorType>(Val: LoadTy)) {
34 if (StoredTy->getScalarType() != LoadTy->getScalarType())
35 return false;
36
37 // If it is known at compile-time that the VScale is larger than one,
38 // use that information to allow for wider loads.
39 const auto &Attrs = F->getAttributes().getFnAttrs();
40 unsigned MinVScale = Attrs.getVScaleRangeMin();
41 MinStoreSize =
42 TypeSize::getFixed(ExactSize: MinStoreSize.getKnownMinValue() * MinVScale);
43 } else if (isFirstClassAggregateOrScalableType(Ty: LoadTy) ||
44 isFirstClassAggregateOrScalableType(Ty: StoredTy)) {
45 return false;
46 }
47
48 // The store size must be byte-aligned to support future type casts.
49 if (llvm::alignTo(Size: MinStoreSize, Align: 8) != MinStoreSize)
50 return false;
51
52 // The store has to be at least as big as the load.
53 if (!TypeSize::isKnownGE(LHS: MinStoreSize, RHS: LoadSize))
54 return false;
55
56 bool StoredNI = DL.isNonIntegralPointerType(Ty: StoredTy->getScalarType());
57 bool LoadNI = DL.isNonIntegralPointerType(Ty: LoadTy->getScalarType());
58 // Don't coerce non-integral pointers to integers or vice versa.
59 if (StoredNI != LoadNI) {
60 // As a special case, allow coercion of memset used to initialize
61 // an array w/null. Despite non-integral pointers not generally having a
62 // specific bit pattern, we do assume null is zero.
63 if (auto *CI = dyn_cast<Constant>(Val: StoredVal))
64 return CI->isNullValue();
65 return false;
66 } else if (StoredNI && LoadNI &&
67 StoredTy->getPointerAddressSpace() !=
68 LoadTy->getPointerAddressSpace()) {
69 return false;
70 }
71
72 // The implementation below uses inttoptr for vectors of unequal size; we
73 // can't allow this for non integral pointers. We could teach it to extract
74 // exact subvectors if desired.
75 if (StoredNI && (StoredTy->isScalableTy() || MinStoreSize != LoadSize))
76 return false;
77
78 if (StoredTy->isTargetExtTy() || LoadTy->isTargetExtTy())
79 return false;
80
81 return true;
82}
83
84/// If we saw a store of a value to memory, and
85/// then a load from a must-aliased pointer of a different type, try to coerce
86/// the stored value. LoadedTy is the type of the load we want to replace.
87/// IRB is IRBuilder used to insert new instructions.
88///
89/// If we can't do it, return null.
90Value *coerceAvailableValueToLoadType(Value *StoredVal, Type *LoadedTy,
91 IRBuilderBase &Helper, Function *F) {
92 assert(canCoerceMustAliasedValueToLoad(StoredVal, LoadedTy, F) &&
93 "precondition violation - materialization can't fail");
94 const DataLayout &DL = F->getDataLayout();
95 if (auto *C = dyn_cast<Constant>(Val: StoredVal))
96 StoredVal = ConstantFoldConstant(C, DL);
97
98 // If this is already the right type, just return it.
99 Type *StoredValTy = StoredVal->getType();
100
101 // If this is a scalable vector forwarded to a fixed vector load, create
102 // a @llvm.vector.extract instead of bitcasts.
103 if (isa<ScalableVectorType>(Val: StoredVal->getType()) &&
104 isa<FixedVectorType>(Val: LoadedTy)) {
105 return Helper.CreateIntrinsic(RetTy: LoadedTy, ID: Intrinsic::vector_extract,
106 Args: {StoredVal, Helper.getInt64(C: 0)});
107 }
108
109 TypeSize StoredValSize = DL.getTypeSizeInBits(Ty: StoredValTy);
110 TypeSize LoadedValSize = DL.getTypeSizeInBits(Ty: LoadedTy);
111
112 // If the store and reload are the same size, we can always reuse it.
113 if (StoredValSize == LoadedValSize) {
114 // Pointer to Pointer -> use bitcast.
115 if (StoredValTy->isPtrOrPtrVectorTy() && LoadedTy->isPtrOrPtrVectorTy()) {
116 StoredVal = Helper.CreateBitCast(V: StoredVal, DestTy: LoadedTy);
117 } else {
118 // Convert source pointers to integers, which can be bitcast.
119 if (StoredValTy->isPtrOrPtrVectorTy()) {
120 StoredValTy = DL.getIntPtrType(StoredValTy);
121 StoredVal = Helper.CreatePtrToInt(V: StoredVal, DestTy: StoredValTy);
122 }
123
124 Type *TypeToCastTo = LoadedTy;
125 if (TypeToCastTo->isPtrOrPtrVectorTy())
126 TypeToCastTo = DL.getIntPtrType(TypeToCastTo);
127
128 if (StoredValTy != TypeToCastTo)
129 StoredVal = Helper.CreateBitCast(V: StoredVal, DestTy: TypeToCastTo);
130
131 // Cast to pointer if the load needs a pointer type.
132 if (LoadedTy->isPtrOrPtrVectorTy())
133 StoredVal = Helper.CreateIntToPtr(V: StoredVal, DestTy: LoadedTy);
134 }
135
136 if (auto *C = dyn_cast<ConstantExpr>(Val: StoredVal))
137 StoredVal = ConstantFoldConstant(C, DL);
138
139 return StoredVal;
140 }
141 // If the loaded value is smaller than the available value, then we can
142 // extract out a piece from it. If the available value is too small, then we
143 // can't do anything.
144 assert(!StoredValSize.isScalable() &&
145 TypeSize::isKnownGE(StoredValSize, LoadedValSize) &&
146 "canCoerceMustAliasedValueToLoad fail");
147
148 // Convert source pointers to integers, which can be manipulated.
149 if (StoredValTy->isPtrOrPtrVectorTy()) {
150 StoredValTy = DL.getIntPtrType(StoredValTy);
151 StoredVal = Helper.CreatePtrToInt(V: StoredVal, DestTy: StoredValTy);
152 }
153
154 // Convert vectors and fp to integer, which can be manipulated.
155 if (!StoredValTy->isIntegerTy()) {
156 StoredValTy = IntegerType::get(C&: StoredValTy->getContext(), NumBits: StoredValSize);
157 StoredVal = Helper.CreateBitCast(V: StoredVal, DestTy: StoredValTy);
158 }
159
160 // If this is a big-endian system, we need to shift the value down to the low
161 // bits so that a truncate will work.
162 if (DL.isBigEndian()) {
163 uint64_t ShiftAmt = DL.getTypeStoreSizeInBits(Ty: StoredValTy).getFixedValue() -
164 DL.getTypeStoreSizeInBits(Ty: LoadedTy).getFixedValue();
165 StoredVal = Helper.CreateLShr(
166 LHS: StoredVal, RHS: ConstantInt::get(Ty: StoredVal->getType(), V: ShiftAmt));
167 }
168
169 // Truncate the integer to the right size now.
170 Type *NewIntTy = IntegerType::get(C&: StoredValTy->getContext(), NumBits: LoadedValSize);
171 StoredVal = Helper.CreateTruncOrBitCast(V: StoredVal, DestTy: NewIntTy);
172
173 if (LoadedTy != NewIntTy) {
174 // If the result is a pointer, inttoptr.
175 if (LoadedTy->isPtrOrPtrVectorTy())
176 StoredVal = Helper.CreateIntToPtr(V: StoredVal, DestTy: LoadedTy);
177 else
178 // Otherwise, bitcast.
179 StoredVal = Helper.CreateBitCast(V: StoredVal, DestTy: LoadedTy);
180 }
181
182 if (auto *C = dyn_cast<Constant>(Val: StoredVal))
183 StoredVal = ConstantFoldConstant(C, DL);
184
185 return StoredVal;
186}
187
188/// This function is called when we have a memdep query of a load that ends up
189/// being a clobbering memory write (store, memset, memcpy, memmove). This
190/// means that the write *may* provide bits used by the load but we can't be
191/// sure because the pointers don't must-alias.
192///
193/// Check this case to see if there is anything more we can do before we give
194/// up. This returns -1 if we have to give up, or a byte number in the stored
195/// value of the piece that feeds the load.
196static int analyzeLoadFromClobberingWrite(Type *LoadTy, Value *LoadPtr,
197 Value *WritePtr,
198 uint64_t WriteSizeInBits,
199 const DataLayout &DL) {
200 // If the loaded/stored value is a first class array/struct, or scalable type,
201 // don't try to transform them. We need to be able to bitcast to integer.
202 if (isFirstClassAggregateOrScalableType(Ty: LoadTy))
203 return -1;
204
205 int64_t StoreOffset = 0, LoadOffset = 0;
206 Value *StoreBase =
207 GetPointerBaseWithConstantOffset(Ptr: WritePtr, Offset&: StoreOffset, DL);
208 Value *LoadBase = GetPointerBaseWithConstantOffset(Ptr: LoadPtr, Offset&: LoadOffset, DL);
209 if (StoreBase != LoadBase)
210 return -1;
211
212 uint64_t LoadSize = DL.getTypeSizeInBits(Ty: LoadTy).getFixedValue();
213
214 if ((WriteSizeInBits & 7) | (LoadSize & 7))
215 return -1;
216 uint64_t StoreSize = WriteSizeInBits / 8; // Convert to bytes.
217 LoadSize /= 8;
218
219 // If the Load isn't completely contained within the stored bits, we don't
220 // have all the bits to feed it. We could do something crazy in the future
221 // (issue a smaller load then merge the bits in) but this seems unlikely to be
222 // valuable.
223 if (StoreOffset > LoadOffset ||
224 StoreOffset + int64_t(StoreSize) < LoadOffset + int64_t(LoadSize))
225 return -1;
226
227 // Okay, we can do this transformation. Return the number of bytes into the
228 // store that the load is.
229 return LoadOffset - StoreOffset;
230}
231
232/// This function is called when we have a
233/// memdep query of a load that ends up being a clobbering store.
234int analyzeLoadFromClobberingStore(Type *LoadTy, Value *LoadPtr,
235 StoreInst *DepSI, const DataLayout &DL) {
236 auto *StoredVal = DepSI->getValueOperand();
237
238 // Cannot handle reading from store of first-class aggregate or scalable type.
239 if (isFirstClassAggregateOrScalableType(Ty: StoredVal->getType()))
240 return -1;
241
242 if (!canCoerceMustAliasedValueToLoad(StoredVal, LoadTy, F: DepSI->getFunction()))
243 return -1;
244
245 Value *StorePtr = DepSI->getPointerOperand();
246 uint64_t StoreSize =
247 DL.getTypeSizeInBits(Ty: DepSI->getValueOperand()->getType()).getFixedValue();
248 return analyzeLoadFromClobberingWrite(LoadTy, LoadPtr, WritePtr: StorePtr, WriteSizeInBits: StoreSize,
249 DL);
250}
251
252/// This function is called when we have a
253/// memdep query of a load that ends up being clobbered by another load. See if
254/// the other load can feed into the second load.
255int analyzeLoadFromClobberingLoad(Type *LoadTy, Value *LoadPtr, LoadInst *DepLI,
256 const DataLayout &DL) {
257 // Cannot handle reading from store of first-class aggregate or scalable type.
258 if (isFirstClassAggregateOrScalableType(Ty: DepLI->getType()))
259 return -1;
260
261 if (!canCoerceMustAliasedValueToLoad(StoredVal: DepLI, LoadTy, F: DepLI->getFunction()))
262 return -1;
263
264 Value *DepPtr = DepLI->getPointerOperand();
265 uint64_t DepSize = DL.getTypeSizeInBits(Ty: DepLI->getType()).getFixedValue();
266 return analyzeLoadFromClobberingWrite(LoadTy, LoadPtr, WritePtr: DepPtr, WriteSizeInBits: DepSize, DL);
267}
268
269int analyzeLoadFromClobberingMemInst(Type *LoadTy, Value *LoadPtr,
270 MemIntrinsic *MI, const DataLayout &DL) {
271 // If the mem operation is a non-constant size, we can't handle it.
272 ConstantInt *SizeCst = dyn_cast<ConstantInt>(Val: MI->getLength());
273 if (!SizeCst)
274 return -1;
275 uint64_t MemSizeInBits = SizeCst->getZExtValue() * 8;
276
277 // If this is memset, we just need to see if the offset is valid in the size
278 // of the memset..
279 if (const auto *memset_inst = dyn_cast<MemSetInst>(Val: MI)) {
280 if (DL.isNonIntegralPointerType(Ty: LoadTy->getScalarType())) {
281 auto *CI = dyn_cast<ConstantInt>(Val: memset_inst->getValue());
282 if (!CI || !CI->isZero())
283 return -1;
284 }
285 return analyzeLoadFromClobberingWrite(LoadTy, LoadPtr, WritePtr: MI->getDest(),
286 WriteSizeInBits: MemSizeInBits, DL);
287 }
288
289 // If we have a memcpy/memmove, the only case we can handle is if this is a
290 // copy from constant memory. In that case, we can read directly from the
291 // constant memory.
292 MemTransferInst *MTI = cast<MemTransferInst>(Val: MI);
293
294 Constant *Src = dyn_cast<Constant>(Val: MTI->getSource());
295 if (!Src)
296 return -1;
297
298 GlobalVariable *GV = dyn_cast<GlobalVariable>(Val: getUnderlyingObject(V: Src));
299 if (!GV || !GV->isConstant() || !GV->hasDefinitiveInitializer())
300 return -1;
301
302 // See if the access is within the bounds of the transfer.
303 int Offset = analyzeLoadFromClobberingWrite(LoadTy, LoadPtr, WritePtr: MI->getDest(),
304 WriteSizeInBits: MemSizeInBits, DL);
305 if (Offset == -1)
306 return Offset;
307
308 // Otherwise, see if we can constant fold a load from the constant with the
309 // offset applied as appropriate.
310 unsigned IndexSize = DL.getIndexTypeSizeInBits(Ty: Src->getType());
311 if (ConstantFoldLoadFromConstPtr(C: Src, Ty: LoadTy, Offset: APInt(IndexSize, Offset), DL))
312 return Offset;
313 return -1;
314}
315
316static Value *getStoreValueForLoadHelper(Value *SrcVal, unsigned Offset,
317 Type *LoadTy, IRBuilderBase &Builder,
318 const DataLayout &DL) {
319 LLVMContext &Ctx = SrcVal->getType()->getContext();
320
321 // If two pointers are in the same address space, they have the same size,
322 // so we don't need to do any truncation, etc. This avoids introducing
323 // ptrtoint instructions for pointers that may be non-integral.
324 if (SrcVal->getType()->isPointerTy() && LoadTy->isPointerTy() &&
325 cast<PointerType>(Val: SrcVal->getType())->getAddressSpace() ==
326 cast<PointerType>(Val: LoadTy)->getAddressSpace()) {
327 return SrcVal;
328 }
329
330 // Return scalable values directly to avoid needing to bitcast to integer
331 // types, as we do not support non-zero Offsets.
332 if (isa<ScalableVectorType>(Val: LoadTy)) {
333 assert(Offset == 0 && "Expected a zero offset for scalable types");
334 return SrcVal;
335 }
336
337 // For the case of a scalable vector being forwarded to a fixed-sized load,
338 // only equal element types are allowed and a @llvm.vector.extract will be
339 // used instead of bitcasts.
340 if (isa<ScalableVectorType>(Val: SrcVal->getType()) &&
341 isa<FixedVectorType>(Val: LoadTy)) {
342 assert(Offset == 0 &&
343 SrcVal->getType()->getScalarType() == LoadTy->getScalarType());
344 return SrcVal;
345 }
346
347 uint64_t StoreSize =
348 (DL.getTypeSizeInBits(Ty: SrcVal->getType()).getFixedValue() + 7) / 8;
349 uint64_t LoadSize = (DL.getTypeSizeInBits(Ty: LoadTy).getFixedValue() + 7) / 8;
350 // Compute which bits of the stored value are being used by the load. Convert
351 // to an integer type to start with.
352 if (SrcVal->getType()->isPtrOrPtrVectorTy())
353 SrcVal =
354 Builder.CreatePtrToInt(V: SrcVal, DestTy: DL.getIntPtrType(SrcVal->getType()));
355 if (!SrcVal->getType()->isIntegerTy())
356 SrcVal =
357 Builder.CreateBitCast(V: SrcVal, DestTy: IntegerType::get(C&: Ctx, NumBits: StoreSize * 8));
358
359 // Shift the bits to the least significant depending on endianness.
360 unsigned ShiftAmt;
361 if (DL.isLittleEndian())
362 ShiftAmt = Offset * 8;
363 else
364 ShiftAmt = (StoreSize - LoadSize - Offset) * 8;
365 if (ShiftAmt)
366 SrcVal = Builder.CreateLShr(LHS: SrcVal,
367 RHS: ConstantInt::get(Ty: SrcVal->getType(), V: ShiftAmt));
368
369 if (LoadSize != StoreSize)
370 SrcVal = Builder.CreateTruncOrBitCast(V: SrcVal,
371 DestTy: IntegerType::get(C&: Ctx, NumBits: LoadSize * 8));
372 return SrcVal;
373}
374
375Value *getValueForLoad(Value *SrcVal, unsigned Offset, Type *LoadTy,
376 Instruction *InsertPt, Function *F) {
377 const DataLayout &DL = F->getDataLayout();
378#ifndef NDEBUG
379 TypeSize MinSrcValSize = DL.getTypeStoreSize(SrcVal->getType());
380 TypeSize LoadSize = DL.getTypeStoreSize(LoadTy);
381 if (MinSrcValSize.isScalable() && !LoadSize.isScalable())
382 MinSrcValSize =
383 TypeSize::getFixed(MinSrcValSize.getKnownMinValue() *
384 F->getAttributes().getFnAttrs().getVScaleRangeMin());
385 assert((MinSrcValSize.isScalable() || Offset + LoadSize <= MinSrcValSize) &&
386 "Expected Offset + LoadSize <= SrcValSize");
387 assert((!MinSrcValSize.isScalable() ||
388 (Offset == 0 && TypeSize::isKnownLE(LoadSize, MinSrcValSize))) &&
389 "Expected offset of zero and LoadSize <= SrcValSize");
390#endif
391 IRBuilder<> Builder(InsertPt);
392 SrcVal = getStoreValueForLoadHelper(SrcVal, Offset, LoadTy, Builder, DL);
393 return coerceAvailableValueToLoadType(StoredVal: SrcVal, LoadedTy: LoadTy, Helper&: Builder, F);
394}
395
396Constant *getConstantValueForLoad(Constant *SrcVal, unsigned Offset,
397 Type *LoadTy, const DataLayout &DL) {
398#ifndef NDEBUG
399 unsigned SrcValSize = DL.getTypeStoreSize(SrcVal->getType()).getFixedValue();
400 unsigned LoadSize = DL.getTypeStoreSize(LoadTy).getFixedValue();
401 assert(Offset + LoadSize <= SrcValSize);
402#endif
403 return ConstantFoldLoadFromConst(C: SrcVal, Ty: LoadTy, Offset: APInt(32, Offset), DL);
404}
405
406/// This function is called when we have a
407/// memdep query of a load that ends up being a clobbering mem intrinsic.
408Value *getMemInstValueForLoad(MemIntrinsic *SrcInst, unsigned Offset,
409 Type *LoadTy, Instruction *InsertPt,
410 const DataLayout &DL) {
411 LLVMContext &Ctx = LoadTy->getContext();
412 uint64_t LoadSize = DL.getTypeSizeInBits(Ty: LoadTy).getFixedValue() / 8;
413 IRBuilder<> Builder(InsertPt);
414
415 // We know that this method is only called when the mem transfer fully
416 // provides the bits for the load.
417 if (MemSetInst *MSI = dyn_cast<MemSetInst>(Val: SrcInst)) {
418 // memset(P, 'x', 1234) -> splat('x'), even if x is a variable, and
419 // independently of what the offset is.
420 Value *Val = MSI->getValue();
421 if (LoadSize != 1)
422 Val =
423 Builder.CreateZExtOrBitCast(V: Val, DestTy: IntegerType::get(C&: Ctx, NumBits: LoadSize * 8));
424 Value *OneElt = Val;
425
426 // Splat the value out to the right number of bits.
427 for (unsigned NumBytesSet = 1; NumBytesSet != LoadSize;) {
428 // If we can double the number of bytes set, do it.
429 if (NumBytesSet * 2 <= LoadSize) {
430 Value *ShVal = Builder.CreateShl(
431 LHS: Val, RHS: ConstantInt::get(Ty: Val->getType(), V: NumBytesSet * 8));
432 Val = Builder.CreateOr(LHS: Val, RHS: ShVal);
433 NumBytesSet <<= 1;
434 continue;
435 }
436
437 // Otherwise insert one byte at a time.
438 Value *ShVal =
439 Builder.CreateShl(LHS: Val, RHS: ConstantInt::get(Ty: Val->getType(), V: 1 * 8));
440 Val = Builder.CreateOr(LHS: OneElt, RHS: ShVal);
441 ++NumBytesSet;
442 }
443
444 return coerceAvailableValueToLoadType(StoredVal: Val, LoadedTy: LoadTy, Helper&: Builder,
445 F: InsertPt->getFunction());
446 }
447
448 // Otherwise, this is a memcpy/memmove from a constant global.
449 MemTransferInst *MTI = cast<MemTransferInst>(Val: SrcInst);
450 Constant *Src = cast<Constant>(Val: MTI->getSource());
451 unsigned IndexSize = DL.getIndexTypeSizeInBits(Ty: Src->getType());
452 return ConstantFoldLoadFromConstPtr(C: Src, Ty: LoadTy, Offset: APInt(IndexSize, Offset),
453 DL);
454}
455
456Constant *getConstantMemInstValueForLoad(MemIntrinsic *SrcInst, unsigned Offset,
457 Type *LoadTy, const DataLayout &DL) {
458 LLVMContext &Ctx = LoadTy->getContext();
459 uint64_t LoadSize = DL.getTypeSizeInBits(Ty: LoadTy).getFixedValue() / 8;
460
461 // We know that this method is only called when the mem transfer fully
462 // provides the bits for the load.
463 if (MemSetInst *MSI = dyn_cast<MemSetInst>(Val: SrcInst)) {
464 auto *Val = dyn_cast<ConstantInt>(Val: MSI->getValue());
465 if (!Val)
466 return nullptr;
467
468 Val = ConstantInt::get(Context&: Ctx, V: APInt::getSplat(NewLen: LoadSize * 8, V: Val->getValue()));
469 return ConstantFoldLoadFromConst(C: Val, Ty: LoadTy, DL);
470 }
471
472 // Otherwise, this is a memcpy/memmove from a constant global.
473 MemTransferInst *MTI = cast<MemTransferInst>(Val: SrcInst);
474 Constant *Src = cast<Constant>(Val: MTI->getSource());
475 unsigned IndexSize = DL.getIndexTypeSizeInBits(Ty: Src->getType());
476 return ConstantFoldLoadFromConstPtr(C: Src, Ty: LoadTy, Offset: APInt(IndexSize, Offset),
477 DL);
478}
479} // namespace VNCoercion
480} // namespace llvm
481