#include "llvm/Analysis/InstructionSimplify.h"
#include "llvm/ADT/SetVector.h"
#include "llvm/ADT/Statistic.h"
-#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Analysis/ConstantFolding.h"
#include "llvm/Analysis/Dominators.h"
#include "llvm/Analysis/ValueTracking.h"
+#include "llvm/Analysis/MemoryBuiltins.h"
#include "llvm/IR/DataLayout.h"
#include "llvm/IR/GlobalAlias.h"
#include "llvm/IR/Operator.h"
/// folding.
static Constant *stripAndComputeConstantOffsets(const DataLayout *TD,
Value *&V) {
- assert(V->getType()->isPointerTy());
+ assert(V->getType()->getScalarType()->isPointerTy());
// Without DataLayout, just be conservative for now. Theoretically, more could
// be done in this case.
} else {
break;
}
- assert(V->getType()->isPointerTy() && "Unexpected operand type!");
+ assert(V->getType()->getScalarType()->isPointerTy() &&
+ "Unexpected operand type!");
} while (Visited.insert(V));
Type *IntPtrTy = TD->getIntPtrType(V->getContext());
- return ConstantInt::get(IntPtrTy, Offset);
+ Constant *OffsetIntPtr = ConstantInt::get(IntPtrTy, Offset);
+ if (V->getType()->isVectorTy())
+ return ConstantVector::getSplat(V->getType()->getVectorNumElements(),
+ OffsetIntPtr);
+ return OffsetIntPtr;
}
/// \brief Compute the constant difference between two pointer values.
return 0;
}
+// A significant optimization not implemented here is assuming that alloca
+// addresses are not equal to incoming argument values. They don't *alias*,
+// as we say, but that doesn't mean they aren't equal, so we take a
+// conservative approach.
+//
+// This is inspired in part by C++11 5.10p1:
+// "Two pointers of the same type compare equal if and only if they are both
+// null, both point to the same function, or both represent the same
+// address."
+//
+// This is pretty permissive.
+//
+// It's also partly due to C11 6.5.9p6:
+// "Two pointers compare equal if and only if both are null pointers, both are
+// pointers to the same object (including a pointer to an object and a
+// subobject at its beginning) or function, both are pointers to one past the
+// last element of the same array object, or one is a pointer to one past the
+// end of one array object and the other is a pointer to the start of a
+// different array object that happens to immediately follow the first array
+// object in the address space.)
+//
+// C11's version is more restrictive, however there's no reason why an argument
+// couldn't be a one-past-the-end value for a stack object in the caller and be
+// equal to the beginning of a stack object in the callee.
+//
+// If the C and C++ standards are ever made sufficiently restrictive in this
+// area, it may be possible to update LLVM's semantics accordingly and reinstate
+// this optimization.
static Constant *computePointerICmp(const DataLayout *TD,
+ const TargetLibraryInfo *TLI,
CmpInst::Predicate Pred,
Value *LHS, Value *RHS) {
+ // First, skip past any trivial no-ops.
+ LHS = LHS->stripPointerCasts();
+ RHS = RHS->stripPointerCasts();
+
+ // A non-null pointer is not equal to a null pointer.
+ if (llvm::isKnownNonNull(LHS) && isa<ConstantPointerNull>(RHS) &&
+ (Pred == CmpInst::ICMP_EQ || Pred == CmpInst::ICMP_NE))
+ return ConstantInt::get(GetCompareTy(LHS),
+ !CmpInst::isTrueWhenEqual(Pred));
+
// We can only fold certain predicates on pointer comparisons.
switch (Pred) {
default:
break;
}
+ // Strip off any constant offsets so that we can reason about them.
+ // It's tempting to use getUnderlyingObject or even just stripInBoundsOffsets
+ // here and compare base addresses like AliasAnalysis does, however there are
+ // numerous hazards. AliasAnalysis and its utilities rely on special rules
+ // governing loads and stores which don't apply to icmps. Also, AliasAnalysis
+ // doesn't need to guarantee pointer inequality when it says NoAlias.
Constant *LHSOffset = stripAndComputeConstantOffsets(TD, LHS);
Constant *RHSOffset = stripAndComputeConstantOffsets(TD, RHS);
- // If LHS and RHS are not related via constant offsets to the same base
- // value, there is nothing we can do here.
- if (LHS != RHS)
- return 0;
+ // If LHS and RHS are related via constant offsets to the same base
+ // value, we can replace it with an icmp which just compares the offsets.
+ if (LHS == RHS)
+ return ConstantExpr::getICmp(Pred, LHSOffset, RHSOffset);
+
+ // Various optimizations for (in)equality comparisons.
+ if (Pred == CmpInst::ICMP_EQ || Pred == CmpInst::ICMP_NE) {
+ // Different non-empty allocations that exist at the same time have
+ // different addresses (if the program can tell). Global variables always
+ // exist, so they always exist during the lifetime of each other and all
+ // allocas. Two different allocas usually have different addresses...
+ //
+ // However, if there's an @llvm.stackrestore dynamically in between two
+ // allocas, they may have the same address. It's tempting to reduce the
+ // scope of the problem by only looking at *static* allocas here. That would
+ // cover the majority of allocas while significantly reducing the likelihood
+ // of having an @llvm.stackrestore pop up in the middle. However, it's not
+ // actually impossible for an @llvm.stackrestore to pop up in the middle of
+ // an entry block. Also, if we have a block that's not attached to a
+ // function, we can't tell if it's "static" under the current definition.
+ // Theoretically, this problem could be fixed by creating a new kind of
+ // instruction kind specifically for static allocas. Such a new instruction
+ // could be required to be at the top of the entry block, thus preventing it
+ // from being subject to a @llvm.stackrestore. Instcombine could even
+ // convert regular allocas into these special allocas. It'd be nifty.
+ // However, until then, this problem remains open.
+ //
+ // So, we'll assume that two non-empty allocas have different addresses
+ // for now.
+ //
+ // With all that, if the offsets are within the bounds of their allocations
+ // (and not one-past-the-end! so we can't use inbounds!), and their
+ // allocations aren't the same, the pointers are not equal.
+ //
+ // Note that it's not necessary to check for LHS being a global variable
+ // address, due to canonicalization and constant folding.
+ if (isa<AllocaInst>(LHS) &&
+ (isa<AllocaInst>(RHS) || isa<GlobalVariable>(RHS))) {
+ ConstantInt *LHSOffsetCI = dyn_cast<ConstantInt>(LHSOffset);
+ ConstantInt *RHSOffsetCI = dyn_cast<ConstantInt>(RHSOffset);
+ uint64_t LHSSize, RHSSize;
+ if (LHSOffsetCI && RHSOffsetCI &&
+ getObjectSize(LHS, LHSSize, TD, TLI) &&
+ getObjectSize(RHS, RHSSize, TD, TLI)) {
+ const APInt &LHSOffsetValue = LHSOffsetCI->getValue();
+ const APInt &RHSOffsetValue = RHSOffsetCI->getValue();
+ if (!LHSOffsetValue.isNegative() &&
+ !RHSOffsetValue.isNegative() &&
+ LHSOffsetValue.ult(LHSSize) &&
+ RHSOffsetValue.ult(RHSSize)) {
+ return ConstantInt::get(GetCompareTy(LHS),
+ !CmpInst::isTrueWhenEqual(Pred));
+ }
+ }
- return ConstantExpr::getICmp(Pred, LHSOffset, RHSOffset);
+ // Repeat the above check but this time without depending on DataLayout
+ // or being able to compute a precise size.
+ if (!cast<PointerType>(LHS->getType())->isEmptyTy() &&
+ !cast<PointerType>(RHS->getType())->isEmptyTy() &&
+ LHSOffset->isNullValue() &&
+ RHSOffset->isNullValue())
+ return ConstantInt::get(GetCompareTy(LHS),
+ !CmpInst::isTrueWhenEqual(Pred));
+ }
+ }
+
+ // Otherwise, fail.
+ return 0;
}
/// SimplifyICmpInst - Given operands for an ICmpInst, see if we can
}
}
- // icmp <object*>, <object*/null> - Different identified objects have
- // different addresses (unless null), and what's more the address of an
- // identified local is never equal to another argument (again, barring null).
- // 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.
- Value *LHSPtr = LHS->stripPointerCasts();
- Value *RHSPtr = RHS->stripPointerCasts();
- if (LHSPtr == RHSPtr)
- return ConstantInt::get(ITy, CmpInst::isTrueWhenEqual(Pred));
-
- // Be more aggressive about stripping pointer adjustments when checking a
- // comparison of an alloca address to another object. We can rip off all
- // inbounds GEP operations, even if they are variable.
- LHSPtr = LHSPtr->stripInBoundsOffsets();
- if (llvm::isIdentifiedObject(LHSPtr)) {
- RHSPtr = RHSPtr->stripInBoundsOffsets();
- if (llvm::isKnownNonNull(LHSPtr) || llvm::isKnownNonNull(RHSPtr)) {
- // If both sides are different identified objects, they aren't equal
- // unless they're null.
- if (LHSPtr != RHSPtr && llvm::isIdentifiedObject(RHSPtr) &&
- Pred == CmpInst::ICMP_EQ)
- return ConstantInt::get(ITy, false);
-
- // A local identified object (alloca or noalias call) can't equal any
- // incoming argument, unless they're both null or they belong to
- // different functions. The latter happens during inlining.
- if (Instruction *LHSInst = dyn_cast<Instruction>(LHSPtr))
- if (Argument *RHSArg = dyn_cast<Argument>(RHSPtr))
- if (LHSInst->getParent()->getParent() == RHSArg->getParent() &&
- Pred == CmpInst::ICMP_EQ)
- return ConstantInt::get(ITy, false);
- }
-
- // Assume that the constant null is on the right.
- if (llvm::isKnownNonNull(LHSPtr) && isa<ConstantPointerNull>(RHSPtr)) {
- if (Pred == CmpInst::ICMP_EQ)
- return ConstantInt::get(ITy, false);
- else if (Pred == CmpInst::ICMP_NE)
- return ConstantInt::get(ITy, true);
- }
- }
-
// If we are comparing with zero then try hard since this is a common case.
if (match(RHS, m_Zero())) {
bool LHSKnownNonNegative, LHSKnownNegative;
// Simplify comparisons of related pointers using a powerful, recursive
// GEP-walk when we have target data available..
if (LHS->getType()->isPointerTy())
- if (Constant *C = computePointerICmp(Q.TD, Pred, LHS, RHS))
+ if (Constant *C = computePointerICmp(Q.TD, Q.TLI, Pred, LHS, RHS))
return C;
if (GetElementPtrInst *GLHS = dyn_cast<GetElementPtrInst>(LHS)) {
RecursionLimit);
}
+static bool IsIdempotent(Intrinsic::ID ID) {
+ switch (ID) {
+ default: return false;
+
+ // Unary idempotent: f(f(x)) = f(x)
+ case Intrinsic::fabs:
+ case Intrinsic::floor:
+ case Intrinsic::ceil:
+ case Intrinsic::trunc:
+ case Intrinsic::rint:
+ case Intrinsic::nearbyint:
+ return true;
+ }
+}
+
+template <typename IterTy>
+static Value *SimplifyIntrinsic(Intrinsic::ID IID, IterTy ArgBegin, IterTy ArgEnd,
+ const Query &Q, unsigned MaxRecurse) {
+ // Perform idempotent optimizations
+ if (!IsIdempotent(IID))
+ return 0;
+
+ // Unary Ops
+ if (std::distance(ArgBegin, ArgEnd) == 1)
+ if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(*ArgBegin))
+ if (II->getIntrinsicID() == IID)
+ return II;
+
+ return 0;
+}
+
template <typename IterTy>
static Value *SimplifyCall(Value *V, IterTy ArgBegin, IterTy ArgEnd,
const Query &Q, unsigned MaxRecurse) {
if (!F)
return 0;
+ if (unsigned IID = F->getIntrinsicID())
+ if (Value *Ret =
+ SimplifyIntrinsic((Intrinsic::ID) IID, ArgBegin, ArgEnd, Q, MaxRecurse))
+ return Ret;
+
if (!canConstantFoldCallTo(F))
return 0;
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