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Make GetMinTrailingZeros a member function of ScalarEvolution, 

so that it can access the TargetData member (when available) and
use ValueTracking.h information to compute information for
SCEVUnknown Values.

Also add GetMinLeadingZeros and GetMinSignBits functions,
with minimal implementations.

llvm-svn: 73794
This commit is contained in:
Dan Gohman 2009-06-19 23:29:04 +00:00
parent cc31110b95
commit c702fc0e64
2 changed files with 97 additions and 22 deletions
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14
llvm/include/llvm/Analysis/ScalarEvolution.h
View File

@ -571,6 +571,20 @@ namespace llvm {
/// is deleted.
void forgetLoopBackedgeTakenCount(const Loop *L);
/// GetMinTrailingZeros - Determine the minimum number of zero bits that S is
/// guaranteed to end in (at every loop iteration). It is, at the same time,
/// the minimum number of times S is divisible by 2. For example, given {4,+,8}
/// it returns 2. If S is guaranteed to be 0, it returns the bitwidth of S.
uint32_t GetMinTrailingZeros(const SCEVHandle &S);
/// GetMinLeadingZeros - Determine the minimum number of zero bits that S is
/// guaranteed to begin with (at every loop iteration).
uint32_t GetMinLeadingZeros(const SCEVHandle &S);
/// GetMinSignBits - Determine the minimum number of sign bits that S is
/// guaranteed to begin with.
uint32_t GetMinSignBits(const SCEVHandle &S);
virtual bool runOnFunction(Function &F);
virtual void releaseMemory();
virtual void getAnalysisUsage(AnalysisUsage &AU) const;

105
llvm/lib/Analysis/ScalarEvolution.cpp
View File

@ -2294,73 +2294,134 @@ SCEVHandle ScalarEvolution::createNodeForGEP(User *GEP) {
/// guaranteed to end in (at every loop iteration). It is, at the same time,
/// the minimum number of times S is divisible by 2. For example, given {4,+,8}
/// it returns 2. If S is guaranteed to be 0, it returns the bitwidth of S.
static uint32_t GetMinTrailingZeros(SCEVHandle S, const ScalarEvolution &SE) {
uint32_t
ScalarEvolution::GetMinTrailingZeros(const SCEVHandle &S) {
if (const SCEVConstant *C = dyn_cast<SCEVConstant>(S))
return C->getValue()->getValue().countTrailingZeros();
if (const SCEVTruncateExpr *T = dyn_cast<SCEVTruncateExpr>(S))
return std::min(GetMinTrailingZeros(T->getOperand(), SE),
(uint32_t)SE.getTypeSizeInBits(T->getType()));
return std::min(GetMinTrailingZeros(T->getOperand()),
(uint32_t)getTypeSizeInBits(T->getType()));
if (const SCEVZeroExtendExpr *E = dyn_cast<SCEVZeroExtendExpr>(S)) {
uint32_t OpRes = GetMinTrailingZeros(E->getOperand(), SE);
return OpRes == SE.getTypeSizeInBits(E->getOperand()->getType()) ?
SE.getTypeSizeInBits(E->getType()) : OpRes;
uint32_t OpRes = GetMinTrailingZeros(E->getOperand());
return OpRes == getTypeSizeInBits(E->getOperand()->getType()) ?
getTypeSizeInBits(E->getType()) : OpRes;
}
if (const SCEVSignExtendExpr *E = dyn_cast<SCEVSignExtendExpr>(S)) {
uint32_t OpRes = GetMinTrailingZeros(E->getOperand(), SE);
return OpRes == SE.getTypeSizeInBits(E->getOperand()->getType()) ?
SE.getTypeSizeInBits(E->getType()) : OpRes;
uint32_t OpRes = GetMinTrailingZeros(E->getOperand());
return OpRes == getTypeSizeInBits(E->getOperand()->getType()) ?
getTypeSizeInBits(E->getType()) : OpRes;
}
if (const SCEVAddExpr *A = dyn_cast<SCEVAddExpr>(S)) {
// The result is the min of all operands results.
uint32_t MinOpRes = GetMinTrailingZeros(A->getOperand(0), SE);
uint32_t MinOpRes = GetMinTrailingZeros(A->getOperand(0));
for (unsigned i = 1, e = A->getNumOperands(); MinOpRes && i != e; ++i)
MinOpRes = std::min(MinOpRes, GetMinTrailingZeros(A->getOperand(i), SE));
MinOpRes = std::min(MinOpRes, GetMinTrailingZeros(A->getOperand(i)));
return MinOpRes;
}
if (const SCEVMulExpr *M = dyn_cast<SCEVMulExpr>(S)) {
// The result is the sum of all operands results.
uint32_t SumOpRes = GetMinTrailingZeros(M->getOperand(0), SE);
uint32_t BitWidth = SE.getTypeSizeInBits(M->getType());
uint32_t SumOpRes = GetMinTrailingZeros(M->getOperand(0));
uint32_t BitWidth = getTypeSizeInBits(M->getType());
for (unsigned i = 1, e = M->getNumOperands();
SumOpRes != BitWidth && i != e; ++i)
SumOpRes = std::min(SumOpRes + GetMinTrailingZeros(M->getOperand(i), SE),
SumOpRes = std::min(SumOpRes + GetMinTrailingZeros(M->getOperand(i)),
BitWidth);
return SumOpRes;
}
if (const SCEVAddRecExpr *A = dyn_cast<SCEVAddRecExpr>(S)) {
// The result is the min of all operands results.
uint32_t MinOpRes = GetMinTrailingZeros(A->getOperand(0), SE);
uint32_t MinOpRes = GetMinTrailingZeros(A->getOperand(0));
for (unsigned i = 1, e = A->getNumOperands(); MinOpRes && i != e; ++i)
MinOpRes = std::min(MinOpRes, GetMinTrailingZeros(A->getOperand(i), SE));
MinOpRes = std::min(MinOpRes, GetMinTrailingZeros(A->getOperand(i)));
return MinOpRes;
}
if (const SCEVSMaxExpr *M = dyn_cast<SCEVSMaxExpr>(S)) {
// The result is the min of all operands results.
uint32_t MinOpRes = GetMinTrailingZeros(M->getOperand(0), SE);
uint32_t MinOpRes = GetMinTrailingZeros(M->getOperand(0));
for (unsigned i = 1, e = M->getNumOperands(); MinOpRes && i != e; ++i)
MinOpRes = std::min(MinOpRes, GetMinTrailingZeros(M->getOperand(i), SE));
MinOpRes = std::min(MinOpRes, GetMinTrailingZeros(M->getOperand(i)));
return MinOpRes;
}
if (const SCEVUMaxExpr *M = dyn_cast<SCEVUMaxExpr>(S)) {
// The result is the min of all operands results.
uint32_t MinOpRes = GetMinTrailingZeros(M->getOperand(0), SE);
uint32_t MinOpRes = GetMinTrailingZeros(M->getOperand(0));
for (unsigned i = 1, e = M->getNumOperands(); MinOpRes && i != e; ++i)
MinOpRes = std::min(MinOpRes, GetMinTrailingZeros(M->getOperand(i), SE));
MinOpRes = std::min(MinOpRes, GetMinTrailingZeros(M->getOperand(i)));
return MinOpRes;
}
// SCEVUDivExpr, SCEVUnknown
if (const SCEVUnknown *U = dyn_cast<SCEVUnknown>(S)) {
// For a SCEVUnknown, ask ValueTracking.
unsigned BitWidth = getTypeSizeInBits(U->getType());
APInt Mask = APInt::getAllOnesValue(BitWidth);
APInt Zeros(BitWidth, 0), Ones(BitWidth, 0);
ComputeMaskedBits(U->getValue(), Mask, Zeros, Ones);
return Zeros.countTrailingOnes();
}
// SCEVUDivExpr
return 0;
}
uint32_t
ScalarEvolution::GetMinLeadingZeros(const SCEVHandle &S) {
// TODO: Handle other SCEV expression types here.
if (const SCEVConstant *C = dyn_cast<SCEVConstant>(S))
return C->getValue()->getValue().countLeadingZeros();
if (const SCEVZeroExtendExpr *C = dyn_cast<SCEVZeroExtendExpr>(S)) {
// A zero-extension cast adds zero bits.
return GetMinLeadingZeros(C->getOperand()) +
(getTypeSizeInBits(C->getType()) -
getTypeSizeInBits(C->getOperand()->getType()));
}
if (const SCEVUnknown *U = dyn_cast<SCEVUnknown>(S)) {
// For a SCEVUnknown, ask ValueTracking.
unsigned BitWidth = getTypeSizeInBits(U->getType());
APInt Mask = APInt::getAllOnesValue(BitWidth);
APInt Zeros(BitWidth, 0), Ones(BitWidth, 0);
ComputeMaskedBits(U->getValue(), Mask, Zeros, Ones, TD);
return Zeros.countLeadingOnes();
}
return 1;
}
uint32_t
ScalarEvolution::GetMinSignBits(const SCEVHandle &S) {
// TODO: Handle other SCEV expression types here.
if (const SCEVConstant *C = dyn_cast<SCEVConstant>(S)) {
const APInt &A = C->getValue()->getValue();
return A.isNegative() ? A.countLeadingOnes() :
A.countLeadingZeros();
}
if (const SCEVSignExtendExpr *C = dyn_cast<SCEVSignExtendExpr>(S)) {
// A sign-extension cast adds sign bits.
return GetMinSignBits(C->getOperand()) +
(getTypeSizeInBits(C->getType()) -
getTypeSizeInBits(C->getOperand()->getType()));
}
if (const SCEVUnknown *U = dyn_cast<SCEVUnknown>(S)) {
// For a SCEVUnknown, ask ValueTracking.
return ComputeNumSignBits(U->getValue(), TD);
}
return 1;
}
/// createSCEV - We know that there is no SCEV for the specified value.
/// Analyze the expression.
///
@ -2430,7 +2491,7 @@ SCEVHandle ScalarEvolution::createSCEV(Value *V) {
if (ConstantInt *CI = dyn_cast<ConstantInt>(U->getOperand(1))) {
SCEVHandle LHS = getSCEV(U->getOperand(0));
const APInt &CIVal = CI->getValue();
if (GetMinTrailingZeros(LHS, *this) >=
if (GetMinTrailingZeros(LHS) >=
(CIVal.getBitWidth() - CIVal.countLeadingZeros()))
return getAddExpr(LHS, getSCEV(U->getOperand(1)));
}