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Move isPointerOffset function to ValueTracking (NFC).
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Summary: To be reused in MemTag sanitizer.

Reviewers: pcc, vitalybuka, ostannard

Subscribers: hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D66165

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@369062 91177308-0d34-0410-b5e6-96231b3b80d8
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@eugenis
eugenis committed Aug 15, 2019
1 parent d2ce08c commit 37d0593
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Showing 3 changed files with 91 additions and 86 deletions.
6 changes: 6 additions & 0 deletions include/llvm/Analysis/ValueTracking.h
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Original file line number Diff line number Diff line change
Expand Up @@ -660,6 +660,12 @@ class Value;
Optional<bool> isImpliedByDomCondition(const Value *Cond,
const Instruction *ContextI,
const DataLayout &DL);

/// Return true if Ptr1 is provably equal to Ptr2 plus a constant offset, and
/// return that constant offset. For example, Ptr1 might be &A[42], and Ptr2
/// might be &A[40]. In this case offset would be -8.
bool isPointerOffset(Value *Ptr1, Value *Ptr2, int64_t &Offset,
const DataLayout &DL);
} // end namespace llvm

#endif // LLVM_ANALYSIS_VALUETRACKING_H
83 changes: 83 additions & 0 deletions lib/Analysis/ValueTracking.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -5701,3 +5701,86 @@ ConstantRange llvm::computeConstantRange(const Value *V, bool UseInstrInfo) {

return CR;
}

static int64_t getOffsetFromIndex(const GEPOperator *GEP, unsigned Idx,
bool &VariableIdxFound,
const DataLayout &DL) {
// Skip over the first indices.
gep_type_iterator GTI = gep_type_begin(GEP);
for (unsigned i = 1; i != Idx; ++i, ++GTI)
/*skip along*/;

// Compute the offset implied by the rest of the indices.
int64_t Offset = 0;
for (unsigned i = Idx, e = GEP->getNumOperands(); i != e; ++i, ++GTI) {
ConstantInt *OpC = dyn_cast<ConstantInt>(GEP->getOperand(i));
if (!OpC)
return VariableIdxFound = true;
if (OpC->isZero())
continue; // No offset.

// Handle struct indices, which add their field offset to the pointer.
if (StructType *STy = GTI.getStructTypeOrNull()) {
Offset += DL.getStructLayout(STy)->getElementOffset(OpC->getZExtValue());
continue;
}

// Otherwise, we have a sequential type like an array or vector. Multiply
// the index by the ElementSize.
uint64_t Size = DL.getTypeAllocSize(GTI.getIndexedType());
Offset += Size * OpC->getSExtValue();
}

return Offset;
}

bool llvm::isPointerOffset(Value *Ptr1, Value *Ptr2, int64_t &Offset,
const DataLayout &DL) {
Ptr1 = Ptr1->stripPointerCasts();
Ptr2 = Ptr2->stripPointerCasts();

// Handle the trivial case first.
if (Ptr1 == Ptr2) {
Offset = 0;
return true;
}

GEPOperator *GEP1 = dyn_cast<GEPOperator>(Ptr1);
GEPOperator *GEP2 = dyn_cast<GEPOperator>(Ptr2);

bool VariableIdxFound = false;

// If one pointer is a GEP and the other isn't, then see if the GEP is a
// constant offset from the base, as in "P" and "gep P, 1".
if (GEP1 && !GEP2 && GEP1->getOperand(0)->stripPointerCasts() == Ptr2) {
Offset = -getOffsetFromIndex(GEP1, 1, VariableIdxFound, DL);
return !VariableIdxFound;
}

if (GEP2 && !GEP1 && GEP2->getOperand(0)->stripPointerCasts() == Ptr1) {
Offset = getOffsetFromIndex(GEP2, 1, VariableIdxFound, DL);
return !VariableIdxFound;
}

// Right now we handle the case when Ptr1/Ptr2 are both GEPs with an identical
// base. After that base, they may have some number of common (and
// potentially variable) indices. After that they handle some constant
// offset, which determines their offset from each other. At this point, we
// handle no other case.
if (!GEP1 || !GEP2 || GEP1->getOperand(0) != GEP2->getOperand(0))
return false;

// Skip any common indices and track the GEP types.
unsigned Idx = 1;
for (; Idx != GEP1->getNumOperands() && Idx != GEP2->getNumOperands(); ++Idx)
if (GEP1->getOperand(Idx) != GEP2->getOperand(Idx))
break;

int64_t Offset1 = getOffsetFromIndex(GEP1, Idx, VariableIdxFound, DL);
int64_t Offset2 = getOffsetFromIndex(GEP2, Idx, VariableIdxFound, DL);
if (VariableIdxFound)
return false;

Offset = Offset2 - Offset1;
return true;
}
88 changes: 2 additions & 86 deletions lib/Transforms/Scalar/MemCpyOptimizer.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -69,90 +69,6 @@ STATISTIC(NumMemSetInfer, "Number of memsets inferred");
STATISTIC(NumMoveToCpy, "Number of memmoves converted to memcpy");
STATISTIC(NumCpyToSet, "Number of memcpys converted to memset");

static int64_t GetOffsetFromIndex(const GEPOperator *GEP, unsigned Idx,
bool &VariableIdxFound,
const DataLayout &DL) {
// Skip over the first indices.
gep_type_iterator GTI = gep_type_begin(GEP);
for (unsigned i = 1; i != Idx; ++i, ++GTI)
/*skip along*/;

// Compute the offset implied by the rest of the indices.
int64_t Offset = 0;
for (unsigned i = Idx, e = GEP->getNumOperands(); i != e; ++i, ++GTI) {
ConstantInt *OpC = dyn_cast<ConstantInt>(GEP->getOperand(i));
if (!OpC)
return VariableIdxFound = true;
if (OpC->isZero()) continue; // No offset.

// Handle struct indices, which add their field offset to the pointer.
if (StructType *STy = GTI.getStructTypeOrNull()) {
Offset += DL.getStructLayout(STy)->getElementOffset(OpC->getZExtValue());
continue;
}

// Otherwise, we have a sequential type like an array or vector. Multiply
// the index by the ElementSize.
uint64_t Size = DL.getTypeAllocSize(GTI.getIndexedType());
Offset += Size*OpC->getSExtValue();
}

return Offset;
}

/// Return true if Ptr1 is provably equal to Ptr2 plus a constant offset, and
/// return that constant offset. For example, Ptr1 might be &A[42], and Ptr2
/// might be &A[40]. In this case offset would be -8.
static bool IsPointerOffset(Value *Ptr1, Value *Ptr2, int64_t &Offset,
const DataLayout &DL) {
Ptr1 = Ptr1->stripPointerCasts();
Ptr2 = Ptr2->stripPointerCasts();

// Handle the trivial case first.
if (Ptr1 == Ptr2) {
Offset = 0;
return true;
}

GEPOperator *GEP1 = dyn_cast<GEPOperator>(Ptr1);
GEPOperator *GEP2 = dyn_cast<GEPOperator>(Ptr2);

bool VariableIdxFound = false;

// If one pointer is a GEP and the other isn't, then see if the GEP is a
// constant offset from the base, as in "P" and "gep P, 1".
if (GEP1 && !GEP2 && GEP1->getOperand(0)->stripPointerCasts() == Ptr2) {
Offset = -GetOffsetFromIndex(GEP1, 1, VariableIdxFound, DL);
return !VariableIdxFound;
}

if (GEP2 && !GEP1 && GEP2->getOperand(0)->stripPointerCasts() == Ptr1) {
Offset = GetOffsetFromIndex(GEP2, 1, VariableIdxFound, DL);
return !VariableIdxFound;
}

// Right now we handle the case when Ptr1/Ptr2 are both GEPs with an identical
// base. After that base, they may have some number of common (and
// potentially variable) indices. After that they handle some constant
// offset, which determines their offset from each other. At this point, we
// handle no other case.
if (!GEP1 || !GEP2 || GEP1->getOperand(0) != GEP2->getOperand(0))
return false;

// Skip any common indices and track the GEP types.
unsigned Idx = 1;
for (; Idx != GEP1->getNumOperands() && Idx != GEP2->getNumOperands(); ++Idx)
if (GEP1->getOperand(Idx) != GEP2->getOperand(Idx))
break;

int64_t Offset1 = GetOffsetFromIndex(GEP1, Idx, VariableIdxFound, DL);
int64_t Offset2 = GetOffsetFromIndex(GEP2, Idx, VariableIdxFound, DL);
if (VariableIdxFound) return false;

Offset = Offset2-Offset1;
return true;
}

namespace {

/// Represents a range of memset'd bytes with the ByteVal value.
Expand Down Expand Up @@ -420,7 +336,7 @@ Instruction *MemCpyOptPass::tryMergingIntoMemset(Instruction *StartInst,

// Check to see if this store is to a constant offset from the start ptr.
int64_t Offset;
if (!IsPointerOffset(StartPtr, NextStore->getPointerOperand(), Offset,
if (!isPointerOffset(StartPtr, NextStore->getPointerOperand(), Offset,
DL))
break;

Expand All @@ -434,7 +350,7 @@ Instruction *MemCpyOptPass::tryMergingIntoMemset(Instruction *StartInst,

// Check to see if this store is to a constant offset from the start ptr.
int64_t Offset;
if (!IsPointerOffset(StartPtr, MSI->getDest(), Offset, DL))
if (!isPointerOffset(StartPtr, MSI->getDest(), Offset, DL))
break;

Ranges.addMemSet(Offset, MSI);
Expand Down

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