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Eliminate cast instructions: use only GEPs in decomposed sequence.

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Don't decompose if there are 2 indices with 0 as first index.
Compute Changed flag correctly in runOnBasicBlock().


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@3233 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Vikram S. Adve 2002-08-03 13:21:15 +00:00
parent a1396a163d
commit 900fd63d12
1 changed files with 71 additions and 82 deletions
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153
lib/Transforms/Scalar/DecomposeMultiDimRefs.cpp
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@ -10,6 +10,7 @@
#include "llvm/Transforms/Scalar.h"
#include "llvm/DerivedTypes.h"
#include "llvm/Constants.h"
#include "llvm/Constant.h"
#include "llvm/iMemory.h"
#include "llvm/iOther.h"
@ -24,14 +25,16 @@ namespace {
virtual bool runOnBasicBlock(BasicBlock &BB);
private:
static void decomposeArrayRef(BasicBlock::iterator &BBI);
static bool decomposeArrayRef(BasicBlock::iterator &BBI);
};
RegisterOpt<DecomposePass> X("lowerrefs", "Decompose multi-dimensional "
"structure/array references");
}
Pass *createDecomposeMultiDimRefsPass() {
Pass
*createDecomposeMultiDimRefsPass()
{
return new DecomposePass();
}
@ -39,113 +42,99 @@ Pass *createDecomposeMultiDimRefsPass() {
// runOnBasicBlock - Entry point for array or structure references with multiple
// indices.
//
bool DecomposePass::runOnBasicBlock(BasicBlock &BB) {
bool
DecomposePass::runOnBasicBlock(BasicBlock &BB)
{
bool Changed = false;
for (BasicBlock::iterator II = BB.begin(); II != BB.end(); ) {
if (MemAccessInst *MAI = dyn_cast<MemAccessInst>(&*II)) {
if (MAI->getNumOperands() > MAI->getFirstIndexOperandNumber()+1) {
decomposeArrayRef(II);
Changed = true;
} else {
++II;
if (MemAccessInst *MAI = dyn_cast<MemAccessInst>(&*II))
if (MAI->getNumIndices() >= 2) {
Changed = decomposeArrayRef(II) || Changed; // always modifies II
continue;
}
} else {
++II;
}
++II;
}
return Changed;
}
//
// For any combination of 2 or more array and structure indices,
// this function repeats the foll. until we have a one-dim. reference: {
// ptr1 = getElementPtr [CompositeType-N] * lastPtr, uint firstIndex
// ptr2 = cast [CompositeType-N] * ptr1 to [CompositeType-N] *
// }
// Then it replaces the original instruction with an equivalent one that
// uses the last ptr2 generated in the loop and a single index.
// If any index is (uint) 0, we omit the getElementPtr instruction.
//
// Check for a constant (uint) 0.
inline bool
IsZero(Value* idx)
{
return (isa<ConstantInt>(idx) && cast<ConstantInt>(idx)->isNullValue());
}
void DecomposePass::decomposeArrayRef(BasicBlock::iterator &BBI) {
// For any MemAccessInst with 2 or more array and structure indices:
//
// opCode CompositeType* P, [uint|ubyte] idx1, ..., [uint|ubyte] idxN
//
// this function generates the foll sequence:
//
// ptr1 = getElementPtr P, idx1
// ptr2 = getElementPtr ptr1, 0, idx2
// ...
// ptrN-1 = getElementPtr ptrN-2, 0, idxN-1
// opCode ptrN-1, 0, idxN // New-MAI
//
// Then it replaces the original instruction with this sequence,
// and replaces all uses of the original instruction with New-MAI.
// If idx1 is 0, we simply omit the first getElementPtr instruction.
//
// On return: BBI points to the instruction after the current one
// (whether or not *BBI was replaced).
//
// Return value: true if the instruction was replaced; false otherwise.
//
bool
DecomposePass::decomposeArrayRef(BasicBlock::iterator &BBI)
{
MemAccessInst &MAI = cast<MemAccessInst>(*BBI);
// If this instr two or fewer arguments and the first argument is 0,
// the decomposed version is identical to the instruction itself.
// This is common enough that it is worth checking for explicitly...
if (MAI.getNumIndices() == 0 ||
(MAI.getNumIndices() <= 2 && IsZero(*MAI.idx_begin()))) {
++BBI;
return false;
}
BasicBlock *BB = MAI.getParent();
Value *LastPtr = MAI.getPointerOperand();
// Remove the instruction from the stream
BB->getInstList().remove(BBI);
// The vector of new instructions to be created
std::vector<Instruction*> NewInsts;
// Process each index except the last one.
//
// Process each index except the last one.
User::const_op_iterator OI = MAI.idx_begin(), OE = MAI.idx_end();
for (; OI+1 != OE; ++OI) {
assert(isa<PointerType>(LastPtr->getType()));
// Check for a zero index. This will need a cast instead of
// a getElementPtr, or it may need neither.
bool indexIsZero = isa<Constant>(*OI) &&
cast<Constant>(OI->get())->isNullValue() &&
OI->get()->getType() == Type::UIntTy;
// Extract the first index. If the ptr is a pointer to a structure
// and the next index is a structure offset (i.e., not an array offset),
// we need to include an initial [0] to index into the pointer.
//
std::vector<Value*> Indices;
const PointerType *PtrTy = cast<PointerType>(LastPtr->getType());
if (isa<StructType>(PtrTy->getElementType())
&& !PtrTy->indexValid(*OI))
// If this is the first index and is 0, skip it and move on!
if (OI == MAI.idx_begin()) {
if (IsZero(*OI)) continue;
} else
// Not the first index: include initial [0] to deref the last ptr
Indices.push_back(Constant::getNullValue(Type::UIntTy));
Indices.push_back(*OI);
// Get the type obtained by applying the first index.
// It must be a structure or array.
const Type *NextTy = MemAccessInst::getIndexedType(LastPtr->getType(),
Indices, true);
assert(isa<CompositeType>(NextTy));
// Get a pointer to the structure or to the elements of the array.
const Type *NextPtrTy =
PointerType::get(isa<StructType>(NextTy) ? NextTy
: cast<ArrayType>(NextTy)->getElementType());
// Instruction 1: nextPtr1 = GetElementPtr LastPtr, Indices
// This is not needed if the index is zero.
if (!indexIsZero) {
LastPtr = new GetElementPtrInst(LastPtr, Indices, "ptr1");
NewInsts.push_back(cast<Instruction>(LastPtr));
++NumAdded;
}
// Instruction 2: nextPtr2 = cast nextPtr1 to NextPtrTy
// This is not needed if the two types are identical.
//
if (LastPtr->getType() != NextPtrTy) {
LastPtr = new CastInst(LastPtr, NextPtrTy, "ptr2");
NewInsts.push_back(cast<Instruction>(LastPtr));
++NumAdded;
}
// New Instruction: nextPtr1 = GetElementPtr LastPtr, Indices
LastPtr = new GetElementPtrInst(LastPtr, Indices, "ptr1");
NewInsts.push_back(cast<Instruction>(LastPtr));
++NumAdded;
}
//
// Now create a new instruction to replace the original one
//
const PointerType *PtrTy = cast<PointerType>(LastPtr->getType());
// First, get the final index vector. As above, we may need an initial [0].
// Get the final index vector, including an initial [0] as before.
std::vector<Value*> Indices;
if (isa<StructType>(PtrTy->getElementType())
&& !PtrTy->indexValid(*OI))
Indices.push_back(Constant::getNullValue(Type::UIntTy));
Indices.push_back(Constant::getNullValue(Type::UIntTy));
Indices.push_back(*OI);
Instruction *NewI = 0;
@ -164,7 +153,6 @@ void DecomposePass::decomposeArrayRef(BasicBlock::iterator &BBI) {
}
NewInsts.push_back(NewI);
// Replace all uses of the old instruction with the new
MAI.replaceAllUsesWith(NewI);
@ -173,8 +161,9 @@ void DecomposePass::decomposeArrayRef(BasicBlock::iterator &BBI) {
// Insert all of the new instructions...
BB->getInstList().insert(BBI, NewInsts.begin(), NewInsts.end());
// Advance the iterator to the instruction following the one just inserted...
BBI = NewInsts.back();
++BBI;
return true;
}