431 lines
17 KiB
C++
431 lines
17 KiB
C++
#include "llvm/Transforms/Utils/VNCoercion.h"
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#include "llvm/Analysis/ConstantFolding.h"
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#include "llvm/Analysis/ValueTracking.h"
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#include "llvm/IR/IRBuilder.h"
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#include "llvm/IR/IntrinsicInst.h"
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#include "llvm/Support/Debug.h"
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#define DEBUG_TYPE "vncoerce"
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namespace llvm {
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namespace VNCoercion {
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static bool isFirstClassAggregateOrScalableType(Type *Ty) {
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return Ty->isStructTy() || Ty->isArrayTy() || isa<ScalableVectorType>(Ty);
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}
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/// Return true if coerceAvailableValueToLoadType will succeed.
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bool canCoerceMustAliasedValueToLoad(Value *StoredVal, Type *LoadTy,
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const DataLayout &DL) {
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Type *StoredTy = StoredVal->getType();
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if (StoredTy == LoadTy)
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return true;
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// If the loaded/stored value is a first class array/struct, or scalable type,
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// don't try to transform them. We need to be able to bitcast to integer.
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if (isFirstClassAggregateOrScalableType(LoadTy) ||
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isFirstClassAggregateOrScalableType(StoredTy))
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return false;
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uint64_t StoreSize = DL.getTypeSizeInBits(StoredTy).getFixedValue();
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// The store size must be byte-aligned to support future type casts.
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if (llvm::alignTo(StoreSize, 8) != StoreSize)
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return false;
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// The store has to be at least as big as the load.
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if (StoreSize < DL.getTypeSizeInBits(LoadTy).getFixedValue())
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return false;
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bool StoredNI = DL.isNonIntegralPointerType(StoredTy->getScalarType());
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bool LoadNI = DL.isNonIntegralPointerType(LoadTy->getScalarType());
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// Don't coerce non-integral pointers to integers or vice versa.
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if (StoredNI != LoadNI) {
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// As a special case, allow coercion of memset used to initialize
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// an array w/null. Despite non-integral pointers not generally having a
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// specific bit pattern, we do assume null is zero.
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if (auto *CI = dyn_cast<Constant>(StoredVal))
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return CI->isNullValue();
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return false;
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} else if (StoredNI && LoadNI &&
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StoredTy->getPointerAddressSpace() !=
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LoadTy->getPointerAddressSpace()) {
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return false;
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}
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// The implementation below uses inttoptr for vectors of unequal size; we
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// can't allow this for non integral pointers. We could teach it to extract
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// exact subvectors if desired.
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if (StoredNI && StoreSize != DL.getTypeSizeInBits(LoadTy).getFixedValue())
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return false;
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if (StoredTy->isTargetExtTy() || LoadTy->isTargetExtTy())
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return false;
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return true;
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}
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/// If we saw a store of a value to memory, and
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/// then a load from a must-aliased pointer of a different type, try to coerce
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/// the stored value. LoadedTy is the type of the load we want to replace.
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/// IRB is IRBuilder used to insert new instructions.
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///
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/// If we can't do it, return null.
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Value *coerceAvailableValueToLoadType(Value *StoredVal, Type *LoadedTy,
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IRBuilderBase &Helper,
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const DataLayout &DL) {
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assert(canCoerceMustAliasedValueToLoad(StoredVal, LoadedTy, DL) &&
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"precondition violation - materialization can't fail");
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if (auto *C = dyn_cast<Constant>(StoredVal))
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StoredVal = ConstantFoldConstant(C, DL);
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// If this is already the right type, just return it.
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Type *StoredValTy = StoredVal->getType();
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uint64_t StoredValSize = DL.getTypeSizeInBits(StoredValTy).getFixedValue();
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uint64_t LoadedValSize = DL.getTypeSizeInBits(LoadedTy).getFixedValue();
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// If the store and reload are the same size, we can always reuse it.
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if (StoredValSize == LoadedValSize) {
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// Pointer to Pointer -> use bitcast.
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if (StoredValTy->isPtrOrPtrVectorTy() && LoadedTy->isPtrOrPtrVectorTy()) {
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StoredVal = Helper.CreateBitCast(StoredVal, LoadedTy);
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} else {
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// Convert source pointers to integers, which can be bitcast.
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if (StoredValTy->isPtrOrPtrVectorTy()) {
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StoredValTy = DL.getIntPtrType(StoredValTy);
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StoredVal = Helper.CreatePtrToInt(StoredVal, StoredValTy);
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}
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Type *TypeToCastTo = LoadedTy;
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if (TypeToCastTo->isPtrOrPtrVectorTy())
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TypeToCastTo = DL.getIntPtrType(TypeToCastTo);
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if (StoredValTy != TypeToCastTo)
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StoredVal = Helper.CreateBitCast(StoredVal, TypeToCastTo);
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// Cast to pointer if the load needs a pointer type.
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if (LoadedTy->isPtrOrPtrVectorTy())
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StoredVal = Helper.CreateIntToPtr(StoredVal, LoadedTy);
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}
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if (auto *C = dyn_cast<ConstantExpr>(StoredVal))
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StoredVal = ConstantFoldConstant(C, DL);
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return StoredVal;
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}
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// If the loaded value is smaller than the available value, then we can
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// extract out a piece from it. If the available value is too small, then we
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// can't do anything.
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assert(StoredValSize >= LoadedValSize &&
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"canCoerceMustAliasedValueToLoad fail");
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// Convert source pointers to integers, which can be manipulated.
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if (StoredValTy->isPtrOrPtrVectorTy()) {
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StoredValTy = DL.getIntPtrType(StoredValTy);
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StoredVal = Helper.CreatePtrToInt(StoredVal, StoredValTy);
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}
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// Convert vectors and fp to integer, which can be manipulated.
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if (!StoredValTy->isIntegerTy()) {
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StoredValTy = IntegerType::get(StoredValTy->getContext(), StoredValSize);
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StoredVal = Helper.CreateBitCast(StoredVal, StoredValTy);
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}
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// If this is a big-endian system, we need to shift the value down to the low
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// bits so that a truncate will work.
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if (DL.isBigEndian()) {
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uint64_t ShiftAmt = DL.getTypeStoreSizeInBits(StoredValTy).getFixedValue() -
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DL.getTypeStoreSizeInBits(LoadedTy).getFixedValue();
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StoredVal = Helper.CreateLShr(
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StoredVal, ConstantInt::get(StoredVal->getType(), ShiftAmt));
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}
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// Truncate the integer to the right size now.
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Type *NewIntTy = IntegerType::get(StoredValTy->getContext(), LoadedValSize);
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StoredVal = Helper.CreateTruncOrBitCast(StoredVal, NewIntTy);
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if (LoadedTy != NewIntTy) {
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// If the result is a pointer, inttoptr.
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if (LoadedTy->isPtrOrPtrVectorTy())
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StoredVal = Helper.CreateIntToPtr(StoredVal, LoadedTy);
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else
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// Otherwise, bitcast.
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StoredVal = Helper.CreateBitCast(StoredVal, LoadedTy);
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}
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if (auto *C = dyn_cast<Constant>(StoredVal))
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StoredVal = ConstantFoldConstant(C, DL);
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return StoredVal;
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}
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/// This function is called when we have a memdep query of a load that ends up
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/// being a clobbering memory write (store, memset, memcpy, memmove). This
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/// means that the write *may* provide bits used by the load but we can't be
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/// sure because the pointers don't must-alias.
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///
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/// Check this case to see if there is anything more we can do before we give
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/// up. This returns -1 if we have to give up, or a byte number in the stored
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/// value of the piece that feeds the load.
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static int analyzeLoadFromClobberingWrite(Type *LoadTy, Value *LoadPtr,
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Value *WritePtr,
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uint64_t WriteSizeInBits,
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const DataLayout &DL) {
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// If the loaded/stored value is a first class array/struct, or scalable type,
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// don't try to transform them. We need to be able to bitcast to integer.
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if (isFirstClassAggregateOrScalableType(LoadTy))
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return -1;
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int64_t StoreOffset = 0, LoadOffset = 0;
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Value *StoreBase =
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GetPointerBaseWithConstantOffset(WritePtr, StoreOffset, DL);
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Value *LoadBase = GetPointerBaseWithConstantOffset(LoadPtr, LoadOffset, DL);
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if (StoreBase != LoadBase)
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return -1;
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uint64_t LoadSize = DL.getTypeSizeInBits(LoadTy).getFixedValue();
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if ((WriteSizeInBits & 7) | (LoadSize & 7))
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return -1;
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uint64_t StoreSize = WriteSizeInBits / 8; // Convert to bytes.
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LoadSize /= 8;
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// If the Load isn't completely contained within the stored bits, we don't
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// have all the bits to feed it. We could do something crazy in the future
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// (issue a smaller load then merge the bits in) but this seems unlikely to be
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// valuable.
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if (StoreOffset > LoadOffset ||
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StoreOffset + int64_t(StoreSize) < LoadOffset + int64_t(LoadSize))
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return -1;
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// Okay, we can do this transformation. Return the number of bytes into the
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// store that the load is.
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return LoadOffset - StoreOffset;
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}
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/// This function is called when we have a
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/// memdep query of a load that ends up being a clobbering store.
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int analyzeLoadFromClobberingStore(Type *LoadTy, Value *LoadPtr,
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StoreInst *DepSI, const DataLayout &DL) {
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auto *StoredVal = DepSI->getValueOperand();
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// Cannot handle reading from store of first-class aggregate or scalable type.
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if (isFirstClassAggregateOrScalableType(StoredVal->getType()))
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return -1;
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if (!canCoerceMustAliasedValueToLoad(StoredVal, LoadTy, DL))
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return -1;
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Value *StorePtr = DepSI->getPointerOperand();
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uint64_t StoreSize =
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DL.getTypeSizeInBits(DepSI->getValueOperand()->getType()).getFixedValue();
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return analyzeLoadFromClobberingWrite(LoadTy, LoadPtr, StorePtr, StoreSize,
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DL);
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}
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/// This function is called when we have a
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/// memdep query of a load that ends up being clobbered by another load. See if
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/// the other load can feed into the second load.
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int analyzeLoadFromClobberingLoad(Type *LoadTy, Value *LoadPtr, LoadInst *DepLI,
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const DataLayout &DL) {
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// Cannot handle reading from store of first-class aggregate yet.
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if (DepLI->getType()->isStructTy() || DepLI->getType()->isArrayTy())
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return -1;
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if (!canCoerceMustAliasedValueToLoad(DepLI, LoadTy, DL))
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return -1;
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Value *DepPtr = DepLI->getPointerOperand();
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uint64_t DepSize = DL.getTypeSizeInBits(DepLI->getType()).getFixedValue();
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return analyzeLoadFromClobberingWrite(LoadTy, LoadPtr, DepPtr, DepSize, DL);
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}
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int analyzeLoadFromClobberingMemInst(Type *LoadTy, Value *LoadPtr,
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MemIntrinsic *MI, const DataLayout &DL) {
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// If the mem operation is a non-constant size, we can't handle it.
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ConstantInt *SizeCst = dyn_cast<ConstantInt>(MI->getLength());
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if (!SizeCst)
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return -1;
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uint64_t MemSizeInBits = SizeCst->getZExtValue() * 8;
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// If this is memset, we just need to see if the offset is valid in the size
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// of the memset..
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if (const auto *memset_inst = dyn_cast<MemSetInst>(MI)) {
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if (DL.isNonIntegralPointerType(LoadTy->getScalarType())) {
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auto *CI = dyn_cast<ConstantInt>(memset_inst->getValue());
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if (!CI || !CI->isZero())
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return -1;
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}
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return analyzeLoadFromClobberingWrite(LoadTy, LoadPtr, MI->getDest(),
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MemSizeInBits, DL);
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}
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// If we have a memcpy/memmove, the only case we can handle is if this is a
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// copy from constant memory. In that case, we can read directly from the
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// constant memory.
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MemTransferInst *MTI = cast<MemTransferInst>(MI);
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Constant *Src = dyn_cast<Constant>(MTI->getSource());
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if (!Src)
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return -1;
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GlobalVariable *GV = dyn_cast<GlobalVariable>(getUnderlyingObject(Src));
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if (!GV || !GV->isConstant() || !GV->hasDefinitiveInitializer())
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return -1;
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// See if the access is within the bounds of the transfer.
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int Offset = analyzeLoadFromClobberingWrite(LoadTy, LoadPtr, MI->getDest(),
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MemSizeInBits, DL);
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if (Offset == -1)
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return Offset;
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// Otherwise, see if we can constant fold a load from the constant with the
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// offset applied as appropriate.
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unsigned IndexSize = DL.getIndexTypeSizeInBits(Src->getType());
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if (ConstantFoldLoadFromConstPtr(Src, LoadTy, APInt(IndexSize, Offset), DL))
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return Offset;
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return -1;
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}
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static Value *getStoreValueForLoadHelper(Value *SrcVal, unsigned Offset,
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Type *LoadTy, IRBuilderBase &Builder,
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const DataLayout &DL) {
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LLVMContext &Ctx = SrcVal->getType()->getContext();
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// If two pointers are in the same address space, they have the same size,
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// so we don't need to do any truncation, etc. This avoids introducing
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// ptrtoint instructions for pointers that may be non-integral.
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if (SrcVal->getType()->isPointerTy() && LoadTy->isPointerTy() &&
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cast<PointerType>(SrcVal->getType())->getAddressSpace() ==
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cast<PointerType>(LoadTy)->getAddressSpace()) {
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return SrcVal;
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}
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uint64_t StoreSize =
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(DL.getTypeSizeInBits(SrcVal->getType()).getFixedValue() + 7) / 8;
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uint64_t LoadSize = (DL.getTypeSizeInBits(LoadTy).getFixedValue() + 7) / 8;
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// Compute which bits of the stored value are being used by the load. Convert
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// to an integer type to start with.
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if (SrcVal->getType()->isPtrOrPtrVectorTy())
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SrcVal =
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Builder.CreatePtrToInt(SrcVal, DL.getIntPtrType(SrcVal->getType()));
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if (!SrcVal->getType()->isIntegerTy())
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SrcVal =
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Builder.CreateBitCast(SrcVal, IntegerType::get(Ctx, StoreSize * 8));
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// Shift the bits to the least significant depending on endianness.
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unsigned ShiftAmt;
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if (DL.isLittleEndian())
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ShiftAmt = Offset * 8;
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else
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ShiftAmt = (StoreSize - LoadSize - Offset) * 8;
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if (ShiftAmt)
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SrcVal = Builder.CreateLShr(SrcVal,
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ConstantInt::get(SrcVal->getType(), ShiftAmt));
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if (LoadSize != StoreSize)
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SrcVal = Builder.CreateTruncOrBitCast(SrcVal,
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IntegerType::get(Ctx, LoadSize * 8));
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return SrcVal;
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}
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Value *getValueForLoad(Value *SrcVal, unsigned Offset, Type *LoadTy,
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Instruction *InsertPt, const DataLayout &DL) {
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#ifndef NDEBUG
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unsigned SrcValSize = DL.getTypeStoreSize(SrcVal->getType()).getFixedValue();
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unsigned LoadSize = DL.getTypeStoreSize(LoadTy).getFixedValue();
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assert(Offset + LoadSize <= SrcValSize);
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#endif
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IRBuilder<> Builder(InsertPt);
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SrcVal = getStoreValueForLoadHelper(SrcVal, Offset, LoadTy, Builder, DL);
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return coerceAvailableValueToLoadType(SrcVal, LoadTy, Builder, DL);
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}
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Constant *getConstantValueForLoad(Constant *SrcVal, unsigned Offset,
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Type *LoadTy, const DataLayout &DL) {
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#ifndef NDEBUG
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unsigned SrcValSize = DL.getTypeStoreSize(SrcVal->getType()).getFixedValue();
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unsigned LoadSize = DL.getTypeStoreSize(LoadTy).getFixedValue();
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assert(Offset + LoadSize <= SrcValSize);
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#endif
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return ConstantFoldLoadFromConst(SrcVal, LoadTy, APInt(32, Offset), DL);
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}
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/// This function is called when we have a
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/// memdep query of a load that ends up being a clobbering mem intrinsic.
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Value *getMemInstValueForLoad(MemIntrinsic *SrcInst, unsigned Offset,
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Type *LoadTy, Instruction *InsertPt,
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const DataLayout &DL) {
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LLVMContext &Ctx = LoadTy->getContext();
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uint64_t LoadSize = DL.getTypeSizeInBits(LoadTy).getFixedValue() / 8;
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IRBuilder<> Builder(InsertPt);
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// We know that this method is only called when the mem transfer fully
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// provides the bits for the load.
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if (MemSetInst *MSI = dyn_cast<MemSetInst>(SrcInst)) {
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// memset(P, 'x', 1234) -> splat('x'), even if x is a variable, and
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// independently of what the offset is.
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Value *Val = MSI->getValue();
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if (LoadSize != 1)
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Val =
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Builder.CreateZExtOrBitCast(Val, IntegerType::get(Ctx, LoadSize * 8));
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Value *OneElt = Val;
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// Splat the value out to the right number of bits.
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for (unsigned NumBytesSet = 1; NumBytesSet != LoadSize;) {
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// If we can double the number of bytes set, do it.
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if (NumBytesSet * 2 <= LoadSize) {
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Value *ShVal = Builder.CreateShl(
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Val, ConstantInt::get(Val->getType(), NumBytesSet * 8));
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Val = Builder.CreateOr(Val, ShVal);
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NumBytesSet <<= 1;
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continue;
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}
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// Otherwise insert one byte at a time.
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Value *ShVal =
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Builder.CreateShl(Val, ConstantInt::get(Val->getType(), 1 * 8));
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Val = Builder.CreateOr(OneElt, ShVal);
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++NumBytesSet;
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}
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return coerceAvailableValueToLoadType(Val, LoadTy, Builder, DL);
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}
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// Otherwise, this is a memcpy/memmove from a constant global.
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MemTransferInst *MTI = cast<MemTransferInst>(SrcInst);
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Constant *Src = cast<Constant>(MTI->getSource());
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unsigned IndexSize = DL.getIndexTypeSizeInBits(Src->getType());
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return ConstantFoldLoadFromConstPtr(Src, LoadTy, APInt(IndexSize, Offset),
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DL);
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}
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Constant *getConstantMemInstValueForLoad(MemIntrinsic *SrcInst, unsigned Offset,
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Type *LoadTy, const DataLayout &DL) {
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LLVMContext &Ctx = LoadTy->getContext();
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uint64_t LoadSize = DL.getTypeSizeInBits(LoadTy).getFixedValue() / 8;
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// We know that this method is only called when the mem transfer fully
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// provides the bits for the load.
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if (MemSetInst *MSI = dyn_cast<MemSetInst>(SrcInst)) {
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auto *Val = dyn_cast<ConstantInt>(MSI->getValue());
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if (!Val)
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return nullptr;
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Val = ConstantInt::get(Ctx, APInt::getSplat(LoadSize * 8, Val->getValue()));
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return ConstantFoldLoadFromConst(Val, LoadTy, DL);
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}
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// Otherwise, this is a memcpy/memmove from a constant global.
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MemTransferInst *MTI = cast<MemTransferInst>(SrcInst);
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Constant *Src = cast<Constant>(MTI->getSource());
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unsigned IndexSize = DL.getIndexTypeSizeInBits(Src->getType());
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return ConstantFoldLoadFromConstPtr(Src, LoadTy, APInt(IndexSize, Offset),
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DL);
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}
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} // namespace VNCoercion
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} // namespace llvm
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