#include "llvm/Analysis/InstructionSimplify.h"
#include "llvm/Analysis/ConstantFolding.h"
#include "llvm/Analysis/Dominators.h"
+#include "llvm/Analysis/ValueTracking.h"
#include "llvm/Support/PatternMatch.h"
#include "llvm/Support/ValueHandle.h"
#include "llvm/Target/TargetData.h"
}
}
- // See if we are doing a comparison with a constant.
+ // icmp <alloca*>, <global/alloca*/null> - Different stack variables have
+ // different addresses, and what's more the address of a stack variable is
+ // never null or equal to the address of a global. Note that generalizing
+ // to the case where LHS is a global variable address or null is pointless,
+ // since if both LHS and RHS are constants then we already constant folded
+ // the compare, and if only one of them is then we moved it to RHS already.
+ if (isa<AllocaInst>(LHS) && (isa<GlobalValue>(RHS) || isa<AllocaInst>(RHS) ||
+ isa<ConstantPointerNull>(RHS)))
+ // We already know that LHS != LHS.
+ return ConstantInt::get(ITy, CmpInst::isFalseWhenEqual(Pred));
+
+ // If we are comparing with zero then try hard since this is a common case.
+ if (match(RHS, m_Zero())) {
+ bool LHSKnownNonNegative, LHSKnownNegative;
+ switch (Pred) {
+ default:
+ assert(false && "Unknown ICmp predicate!");
+ case ICmpInst::ICMP_ULT:
+ return ConstantInt::getFalse(LHS->getContext());
+ case ICmpInst::ICMP_UGE:
+ return ConstantInt::getTrue(LHS->getContext());
+ case ICmpInst::ICMP_EQ:
+ case ICmpInst::ICMP_ULE:
+ if (isKnownNonZero(LHS, TD))
+ return ConstantInt::getFalse(LHS->getContext());
+ break;
+ case ICmpInst::ICMP_NE:
+ case ICmpInst::ICMP_UGT:
+ if (isKnownNonZero(LHS, TD))
+ return ConstantInt::getTrue(LHS->getContext());
+ break;
+ case ICmpInst::ICMP_SLT:
+ ComputeSignBit(LHS, LHSKnownNonNegative, LHSKnownNegative, TD);
+ if (LHSKnownNegative)
+ return ConstantInt::getTrue(LHS->getContext());
+ if (LHSKnownNonNegative)
+ return ConstantInt::getFalse(LHS->getContext());
+ break;
+ case ICmpInst::ICMP_SLE:
+ ComputeSignBit(LHS, LHSKnownNonNegative, LHSKnownNegative, TD);
+ if (LHSKnownNegative)
+ return ConstantInt::getTrue(LHS->getContext());
+ if (LHSKnownNonNegative && isKnownNonZero(LHS, TD))
+ return ConstantInt::getFalse(LHS->getContext());
+ break;
+ case ICmpInst::ICMP_SGE:
+ ComputeSignBit(LHS, LHSKnownNonNegative, LHSKnownNegative, TD);
+ if (LHSKnownNegative)
+ return ConstantInt::getFalse(LHS->getContext());
+ if (LHSKnownNonNegative)
+ return ConstantInt::getTrue(LHS->getContext());
+ break;
+ case ICmpInst::ICMP_SGT:
+ ComputeSignBit(LHS, LHSKnownNonNegative, LHSKnownNegative, TD);
+ if (LHSKnownNegative)
+ return ConstantInt::getFalse(LHS->getContext());
+ if (LHSKnownNonNegative && isKnownNonZero(LHS, TD))
+ return ConstantInt::getTrue(LHS->getContext());
+ break;
+ }
+ }
+
+ // See if we are doing a comparison with a constant integer.
if (ConstantInt *CI = dyn_cast<ConstantInt>(RHS)) {
switch (Pred) {
default: break;
}
}
- // icmp <alloca*>, <global/alloca*/null> - Different stack variables have
- // different addresses, and what's more the address of a stack variable is
- // never null or equal to the address of a global. Note that generalizing
- // to the case where LHS is a global variable address or null is pointless,
- // since if both LHS and RHS are constants then we already constant folded
- // the compare, and if only one of them is then we moved it to RHS already.
- if (isa<AllocaInst>(LHS) && (isa<GlobalValue>(RHS) || isa<AllocaInst>(RHS) ||
- isa<ConstantPointerNull>(RHS)))
- // We already know that LHS != LHS.
- return ConstantInt::get(ITy, CmpInst::isFalseWhenEqual(Pred));
-
// Compare of cast, for example (zext X) != 0 -> X != 0
if (isa<CastInst>(LHS) && (isa<Constant>(RHS) || isa<CastInst>(RHS))) {
Instruction *LI = cast<CastInst>(LHS);
#include "llvm/Target/TargetData.h"
#include "llvm/Support/GetElementPtrTypeIterator.h"
#include "llvm/Support/MathExtras.h"
+#include "llvm/Support/PatternMatch.h"
#include "llvm/ADT/SmallPtrSet.h"
#include <cstring>
using namespace llvm;
+using namespace llvm::PatternMatch;
+
+const unsigned MaxDepth = 6;
+
+/// getBitWidth - Returns the bitwidth of the given scalar or pointer type (if
+/// unknown returns 0). For vector types, returns the element type's bitwidth.
+static unsigned getBitWidth(const Type *Ty, const TargetData *TD) {
+ if (unsigned BitWidth = Ty->getScalarSizeInBits())
+ return BitWidth;
+ assert(isa<PointerType>(Ty) && "Expected a pointer type!");
+ return TD ? TD->getPointerSizeInBits() : 0;
+}
/// ComputeMaskedBits - Determine which of the bits specified in Mask are
/// known to be either zero or one and return them in the KnownZero/KnownOne
void llvm::ComputeMaskedBits(Value *V, const APInt &Mask,
APInt &KnownZero, APInt &KnownOne,
const TargetData *TD, unsigned Depth) {
- const unsigned MaxDepth = 6;
assert(V && "No Value?");
assert(Depth <= MaxDepth && "Limit Search Depth");
unsigned BitWidth = Mask.getBitWidth();
}
}
+/// ComputeSignBit - Determine whether the sign bit is known to be zero or
+/// one. Convenience wrapper around ComputeMaskedBits.
+void llvm::ComputeSignBit(Value *V, bool &KnownZero, bool &KnownOne,
+ const TargetData *TD, unsigned Depth) {
+ unsigned BitWidth = getBitWidth(V->getType(), TD);
+ if (!BitWidth) {
+ KnownZero = false;
+ KnownOne = false;
+ return;
+ }
+ APInt ZeroBits(BitWidth, 0);
+ APInt OneBits(BitWidth, 0);
+ ComputeMaskedBits(V, APInt::getSignBit(BitWidth), ZeroBits, OneBits, TD,
+ Depth);
+ KnownOne = OneBits[BitWidth - 1];
+ KnownZero = ZeroBits[BitWidth - 1];
+}
+
+/// isPowerOfTwo - Return true if the given value is known to have exactly one
+/// bit set when defined. For vectors return true if every element is known to
+/// be a power of two when defined. Supports values with integer or pointer
+/// types and vectors of integers.
+bool llvm::isPowerOfTwo(Value *V, const TargetData *TD, unsigned Depth) {
+ if (ConstantInt *CI = dyn_cast<ConstantInt>(V))
+ return CI->getValue().countPopulation() == 1;
+ // TODO: Handle vector constants.
+
+ // 1 << X is clearly a power of two if the one is not shifted off the end. If
+ // it is shifted off the end then the result is undefined.
+ if (match(V, m_Shl(m_One(), m_Value())))
+ return true;
+
+ // (signbit) >>l X is clearly a power of two if the one is not shifted off the
+ // bottom. If it is shifted off the bottom then the result is undefined.
+ ConstantInt *CI;
+ if (match(V, m_LShr(m_ConstantInt(CI), m_Value())) &&
+ CI->getValue().isSignBit())
+ return true;
+
+ // The remaining tests are all recursive, so bail out if we hit the limit.
+ if (Depth++ == MaxDepth)
+ return false;
+
+ if (ZExtInst *ZI = dyn_cast<ZExtInst>(V))
+ return isPowerOfTwo(ZI->getOperand(0), TD, Depth);
+
+ if (SelectInst *SI = dyn_cast<SelectInst>(V))
+ return isPowerOfTwo(SI->getTrueValue(), TD, Depth) &&
+ isPowerOfTwo(SI->getFalseValue(), TD, Depth);
+
+ return false;
+}
+
+/// isKnownNonZero - Return true if the given value is known to be non-zero
+/// when defined. For vectors return true if every element is known to be
+/// non-zero when defined. Supports values with integer or pointer type and
+/// vectors of integers.
+bool llvm::isKnownNonZero(Value *V, const TargetData *TD, unsigned Depth) {
+ if (Constant *C = dyn_cast<Constant>(V)) {
+ if (C->isNullValue())
+ return false;
+ if (isa<ConstantInt>(C))
+ // Must be non-zero due to null test above.
+ return true;
+ // TODO: Handle vectors
+ return false;
+ }
+
+ // The remaining tests are all recursive, so bail out if we hit the limit.
+ if (Depth++ == MaxDepth)
+ return false;
+
+ unsigned BitWidth = getBitWidth(V->getType(), TD);
+
+ // X | Y != 0 if X != 0 or Y != 0.
+ Value *X = 0, *Y = 0;
+ if (match(V, m_Or(m_Value(X), m_Value(Y))))
+ return isKnownNonZero(X, TD, Depth) || isKnownNonZero(Y, TD, Depth);
+
+ // ext X != 0 if X != 0.
+ if (isa<SExtInst>(V) || isa<ZExtInst>(V))
+ return isKnownNonZero(cast<Instruction>(V)->getOperand(0), TD, Depth);
+
+ // shl X, A != 0 if X is odd. Note that the value of the shift is undefined
+ // if the lowest bit is shifted off the end.
+ if (BitWidth && match(V, m_Shl(m_Value(X), m_Value(Y)))) {
+ APInt KnownZero(BitWidth, 0);
+ APInt KnownOne(BitWidth, 0);
+ ComputeMaskedBits(V, APInt(BitWidth, 1), KnownZero, KnownOne, TD, Depth);
+ if (KnownOne[0])
+ return true;
+ }
+ // shr X, A != 0 if X is negative. Note that the value of the shift is not
+ // defined if the sign bit is shifted off the end.
+ else if (match(V, m_Shr(m_Value(X), m_Value(Y)))) {
+ bool XKnownNonNegative, XKnownNegative;
+ ComputeSignBit(X, XKnownNonNegative, XKnownNegative, TD, Depth);
+ if (XKnownNegative)
+ return true;
+ }
+ // X + Y.
+ else if (match(V, m_Add(m_Value(X), m_Value(Y)))) {
+ bool XKnownNonNegative, XKnownNegative;
+ bool YKnownNonNegative, YKnownNegative;
+ ComputeSignBit(X, XKnownNonNegative, XKnownNegative, TD, Depth);
+ ComputeSignBit(Y, YKnownNonNegative, YKnownNegative, TD, Depth);
+
+ // If X and Y are both non-negative (as signed values) then their sum is not
+ // zero.
+ if (XKnownNonNegative && YKnownNonNegative)
+ return true;
+
+ // If X and Y are both negative (as signed values) then their sum is not
+ // zero unless both X and Y equal INT_MIN.
+ if (BitWidth && XKnownNegative && YKnownNegative) {
+ APInt KnownZero(BitWidth, 0);
+ APInt KnownOne(BitWidth, 0);
+ APInt Mask = APInt::getSignedMaxValue(BitWidth);
+ // The sign bit of X is set. If some other bit is set then X is not equal
+ // to INT_MIN.
+ ComputeMaskedBits(X, Mask, KnownZero, KnownOne, TD, Depth);
+ if ((KnownOne & Mask) != 0)
+ return true;
+ // The sign bit of Y is set. If some other bit is set then Y is not equal
+ // to INT_MIN.
+ ComputeMaskedBits(Y, Mask, KnownZero, KnownOne, TD, Depth);
+ if ((KnownOne & Mask) != 0)
+ return true;
+ }
+
+ // The sum of a non-negative number and a power of two is not zero.
+ if (XKnownNonNegative && isPowerOfTwo(Y, TD, Depth))
+ return true;
+ if (YKnownNonNegative && isPowerOfTwo(X, TD, Depth))
+ return true;
+ }
+ // (C ? X : Y) != 0 if X != 0 and Y != 0.
+ else if (SelectInst *SI = dyn_cast<SelectInst>(V)) {
+ if (isKnownNonZero(SI->getTrueValue(), TD, Depth) &&
+ isKnownNonZero(SI->getFalseValue(), TD, Depth))
+ return true;
+ }
+
+ if (!BitWidth) return false;
+ APInt KnownZero(BitWidth, 0);
+ APInt KnownOne(BitWidth, 0);
+ ComputeMaskedBits(V, APInt::getAllOnesValue(BitWidth), KnownZero, KnownOne,
+ TD, Depth);
+ return KnownOne != 0;
+}
+
/// MaskedValueIsZero - Return true if 'V & Mask' is known to be zero. We use
/// this predicate to simplify operations downstream. Mask is known to be zero
/// for bits that V cannot have.
projects / oota-llvm.git / commitdiff