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Symbolically evaluate constant expressions like &A[123] - &A[4].f.

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This occurs in C++ code like:

#include <iostream>
#include <iterator>
int a[] = { 1, 2, 3, 4, 5 };
int main() {
  using namespace std;
  copy(a, a + sizeof(a)/sizeof(a[0]), ostream_iterator<int>(cout, "\n"));
  return 0;
}

Before we would decide the loop trip count is:
sdiv (i32 sub (i32 ptrtoint (i32* getelementptr ([5 x i32]* @a, i32 0, i32 5) to i32), i32 ptrtoint ([5 x i32]* @a to i32)), i32 4)

Now we decide it is "5".  Amazing.

This code will need to be refactored, but I'm doing that as a separate
commit.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@33665 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2007-01-30 22:32:46 +00:00
parent c60e76d139
commit c5eff4488b
1 changed files with 143 additions and 2 deletions
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145
lib/Transforms/Scalar/InstructionCombining.cpp
View File

@ -1355,6 +1355,63 @@ Value *InstCombiner::SimplifyDemandedVectorElts(Value *V, uint64_t DemandedElts,
break;
}
case Instruction::BitCast: {
// packed->packed
const PackedType *PTy = dyn_cast<PackedType>(I->getOperand(0)->getType());
if (!PTy) break;
unsigned InVWidth = PTy->getNumElements();
uint64_t InputDemandedElts = 0;
unsigned Ratio;
if (VWidth == InVWidth) {
Ratio = 1;
InputDemandedElts = DemandedElts;
} else if (VWidth > InVWidth) {
// If there are more elements in the result than there are in the source,
// then an input element is live if any of the corresponding output
// elements are live.
Ratio = VWidth/InVWidth;
for (unsigned OutIdx = 0; OutIdx != VWidth; ++OutIdx) {
if (DemandedElts & (1ULL << OutIdx))
InputDemandedElts |= 1ULL << (OutIdx/Ratio);
}
} else {
// If there are more elements in the source than there are in the result,
// then an input element is live if the corresponding output element is
// live.
Ratio = InVWidth/VWidth;
for (unsigned InIdx = 0; InIdx != InVWidth; ++InIdx)
if (DemandedElts & (1ULL << InIdx/Ratio))
InputDemandedElts |= 1ULL << InIdx;
}
// div/rem demand all inputs, because they don't want divide by zero.
TmpV = SimplifyDemandedVectorElts(I->getOperand(0), InputDemandedElts,
UndefElts2, Depth+1);
if (TmpV) {
I->setOperand(0, TmpV);
MadeChange = true;
}
UndefElts = UndefElts2;
if (VWidth > InVWidth) {
// If there are more elements in the result than there are in the source,
// then an output element is undef if the corresponding input element is
// undef.
for (unsigned OutIdx = 0; OutIdx != VWidth; ++OutIdx)
if (UndefElts2 & (1ULL << (OutIdx/Ratio)))
UndefElts |= 1ULL << OutIdx;
} else if (VWidth < InVWidth) {
// If there are more elements in the source than there are in the result,
// then a result element is undef if all of the corresponding input
// elements are undef.
UndefElts = ~0ULL >> (64-VWidth); // Start out all undef.
for (unsigned InIdx = 0; InIdx != InVWidth; ++InIdx)
if ((UndefElts2 & (1ULL << InIdx)) == 0) // Not undef?
UndefElts &= ~(1ULL << (InIdx/Ratio)); // Clear undef bit.
}
break;
}
case Instruction::And:
case Instruction::Or:
case Instruction::Xor:
@ -1756,7 +1813,8 @@ Instruction *InstCombiner::visitAdd(BinaryOperator &I) {
ConstantInt *XorRHS = 0;
Value *XorLHS = 0;
if (match(LHS, m_Xor(m_Value(XorLHS), m_ConstantInt(XorRHS)))) {
if (isa<ConstantInt>(RHSC) &&
match(LHS, m_Xor(m_Value(XorLHS), m_ConstantInt(XorRHS)))) {
unsigned TySizeBits = I.getType()->getPrimitiveSizeInBits();
int64_t RHSSExt = cast<ConstantInt>(RHSC)->getSExtValue();
uint64_t RHSZExt = cast<ConstantInt>(RHSC)->getZExtValue();
@ -8985,7 +9043,14 @@ Instruction *InstCombiner::visitShuffleVectorInst(ShuffleVectorInst &SVI) {
}
}
}
// See if SimplifyDemandedVectorElts can simplify based on this shuffle. For
// example, if this is a splat, then we only demand from one input element.
uint64_t UndefElts;
if (Value *V = SimplifyDemandedVectorElts(&SVI, (1ULL << Mask.size())-1,
UndefElts))
return ReplaceInstUsesWith(SVI, V);
return MadeChange ? &SVI : 0;
}
@ -9028,6 +9093,58 @@ static bool TryToSinkInstruction(Instruction *I, BasicBlock *DestBlock) {
return true;
}
/// IsConstantOffsetFromGlobal - If this constant is actually a constant offset
/// from a global, return the global and the constant. Because of
/// constantexprs, this function is recursive.
static bool IsConstantOffsetFromGlobal(Constant *C, GlobalValue *&GV,
int64_t &Offset, const TargetData &TD) {
// Trivial case, constant is the global.
if ((GV = dyn_cast<GlobalValue>(C))) {
Offset = 0;
return true;
}
// Otherwise, if this isn't a constant expr, bail out.
ConstantExpr *CE = dyn_cast<ConstantExpr>(C);
if (!CE) return false;
// Look through ptr->int and ptr->ptr casts.
if (CE->getOpcode() == Instruction::PtrToInt ||
CE->getOpcode() == Instruction::BitCast)
return IsConstantOffsetFromGlobal(CE->getOperand(0), GV, Offset, TD);
// i32* getelementptr ([5 x i32]* @a, i32 0, i32 5)
if (CE->getOpcode() == Instruction::GetElementPtr) {
// Cannot compute this if the element type of the pointer is missing size
// info.
if (!cast<PointerType>(CE->getOperand(0)->getType())->getElementType()->isSized())
return false;
// If the base isn't a global+constant, we aren't either.
if (!IsConstantOffsetFromGlobal(CE->getOperand(0), GV, Offset, TD))
return false;
// Otherwise, add any offset that our operands provide.
gep_type_iterator GTI = gep_type_begin(CE);
for (unsigned i = 1, e = CE->getNumOperands(); i != e; ++i, ++GTI) {
ConstantInt *CI = dyn_cast<ConstantInt>(CE->getOperand(i));
if (!CI) return false; // Index isn't a simple constant?
if (CI->getZExtValue() == 0) continue; // Not adding anything.
if (const StructType *ST = dyn_cast<StructType>(*GTI)) {
// N = N + Offset
Offset += TD.getStructLayout(ST)->MemberOffsets[CI->getZExtValue()];
} else {
const SequentialType *ST = cast<SequentialType>(*GTI);
Offset += TD.getTypeSize(ST->getElementType())*CI->getSExtValue();
}
}
return true;
}
return false;
}
/// OptimizeConstantExpr - Given a constant expression and target data layout
/// information, symbolically evaluate the constant expr to something simpler
/// if possible.
@ -9051,6 +9168,30 @@ static Constant *OptimizeConstantExpr(ConstantExpr *CE, const TargetData *TD) {
}
}
// SROA
// Fold (and 0xffffffff00000000, (shl x, 32)) -> shl.
// Fold (lshr (or X, Y), 32) -> (lshr [X/Y], 32) if one doesn't contribute
// bits.
// If the constant expr is something like &A[123] - &A[4].f, fold this into a
// constant. This happens frequently when iterating over a global array.
if (CE->getOpcode() == Instruction::Sub) {
GlobalValue *GV1, *GV2;
int64_t Offs1, Offs2;
if (IsConstantOffsetFromGlobal(CE->getOperand(0), GV1, Offs1, *TD))
if (IsConstantOffsetFromGlobal(CE->getOperand(1), GV2, Offs2, *TD) &&
GV1 == GV2) {
// (&GV+C1) - (&GV+C2) -> C1-C2, pointer arithmetic cannot overflow.
return ConstantInt::get(CE->getType(), Offs1-Offs2);
}
}
// TODO: Fold icmp setne/seteq as well.
return CE;
}