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Address some review comments from Duncan. This moves the iterative

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offset accumulation to use a boring APInt instead of ConstantExprs.
I didn't go all the way to an 'int64_t' because I wanted APInt to handle
any magic required to properly wrap the arithmetic when the pointer
width is <64 bits. If there is a significant penalty from using APInt
here, first off WTF, and secondly let me know and I'll do the math by
hand.

I've left one layer still operating w/ ConstantExpr because it makes the
interface quite a bit simpler, and that one isn't iterative so has much
lower cost.

I suppose this may potentially speed up some strang compilation
situations, but I don't really expect much. It should have no functional
impact either way.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@152590 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chandler Carruth 2012-03-13 00:06:15 +00:00
parent f5677777ca
commit 90c14fcb7e
1 changed files with 23 additions and 32 deletions
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55
lib/Analysis/InstructionSimplify.cpp
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@ -667,47 +667,39 @@ Value *llvm::SimplifyAddInst(Value *Op0, Value *Op1, bool isNSW, bool isNUW,
return ::SimplifyAddInst(Op0, Op1, isNSW, isNUW, TD, TLI, DT, RecursionLimit);
}
/// \brief Compute the constant integer offset a GEP represents.
/// \brief Accumulate the constant integer offset a GEP represents.
///
/// Given a getelementptr instruction/constantexpr, form a constant expression
/// which computes the offset from the base pointer (without adding in the base
/// pointer).
static Constant *computeGEPOffset(const TargetData &TD, GEPOperator *GEP) {
Type *IntPtrTy = TD.getIntPtrType(GEP->getContext());
Constant *Result = Constant::getNullValue(IntPtrTy);
// If the GEP is inbounds, we know that none of the addressing operations will
// overflow in an unsigned sense.
bool IsInBounds = GEP->isInBounds();
// Build a mask for high order bits.
/// Given a getelementptr instruction/constantexpr, accumulate the constant
/// offset from the base pointer into the provided APInt 'Offset'. Returns true
/// if the GEP has all-constant indices. Returns false if any non-constant
/// index is encountered leaving the 'Offset' in an undefined state. The
/// 'Offset' APInt must be the bitwidth of the target's pointer size.
static bool accumulateGEPOffset(const TargetData &TD, GEPOperator *GEP,
APInt &Offset) {
unsigned IntPtrWidth = TD.getPointerSizeInBits();
uint64_t PtrSizeMask = ~0ULL >> (64-IntPtrWidth);
assert(IntPtrWidth == Offset.getBitWidth());
gep_type_iterator GTI = gep_type_begin(GEP);
for (User::op_iterator I = GEP->op_begin() + 1, E = GEP->op_end(); I != E;
++I, ++GTI) {
ConstantInt *OpC = dyn_cast<ConstantInt>(*I);
if (!OpC) return 0;
if (!OpC) return false;
if (OpC->isZero()) continue;
uint64_t Size = TD.getTypeAllocSize(GTI.getIndexedType()) & PtrSizeMask;
// Handle a struct index, which adds its field offset to the pointer.
if (StructType *STy = dyn_cast<StructType>(*GTI)) {
Size = TD.getStructLayout(STy)->getElementOffset(OpC->getZExtValue());
if (Size)
Result = ConstantExpr::getAdd(Result, ConstantInt::get(IntPtrTy, Size));
unsigned ElementIdx = OpC->getZExtValue();
const StructLayout *SL = TD.getStructLayout(STy);
Offset += APInt(IntPtrWidth, SL->getElementOffset(ElementIdx),
/*isSigned=*/true);
continue;
}
Constant *Scale = ConstantInt::get(IntPtrTy, Size);
Constant *OC = ConstantExpr::getIntegerCast(OpC, IntPtrTy, true /*SExt*/);
Scale = ConstantExpr::getMul(OC, Scale, IsInBounds/*NUW*/);
Result = ConstantExpr::getAdd(Result, Scale);
APInt TypeSize(IntPtrWidth, TD.getTypeAllocSize(GTI.getIndexedType()),
/*isSigned=*/true);
Offset += OpC->getValue().sextOrTrunc(IntPtrWidth) * TypeSize;
}
return Result;
return true;
}
/// \brief Compute the base pointer and cumulative constant offsets for V.
@ -721,8 +713,8 @@ static Constant *stripAndComputeConstantOffsets(const TargetData &TD,
if (!V->getType()->isPointerTy())
return 0;
Type *IntPtrTy = TD.getIntPtrType(V->getContext());
Constant *Result = Constant::getNullValue(IntPtrTy);
unsigned IntPtrWidth = TD.getPointerSizeInBits();
APInt Offset = APInt::getNullValue(IntPtrWidth);
// Even though we don't look through PHI nodes, we could be called on an
// instruction in an unreachable block, which may be on a cycle.
@ -730,10 +722,8 @@ static Constant *stripAndComputeConstantOffsets(const TargetData &TD,
Visited.insert(V);
do {
if (GEPOperator *GEP = dyn_cast<GEPOperator>(V)) {
Constant *Offset = computeGEPOffset(TD, GEP);
if (!Offset)
if (!accumulateGEPOffset(TD, GEP, Offset))
break;
Result = ConstantExpr::getAdd(Result, Offset);
V = GEP->getPointerOperand();
} else if (Operator::getOpcode(V) == Instruction::BitCast) {
V = cast<Operator>(V)->getOperand(0);
@ -747,7 +737,8 @@ static Constant *stripAndComputeConstantOffsets(const TargetData &TD,
assert(V->getType()->isPointerTy() && "Unexpected operand type!");
} while (Visited.insert(V));
return Result;
Type *IntPtrTy = TD.getIntPtrType(V->getContext());
return ConstantInt::get(IntPtrTy, Offset);
}
/// \brief Compute the constant difference between two pointer values.