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a sequence of 1-D references, using a sequence of getElementPtrs. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@1907 91177308-0d34-0410-b5e6-96231b3b80d8
149 lines
5.3 KiB
C++
149 lines
5.3 KiB
C++
//===- llvm/Transforms/DecomposeArrayRefs.cpp - Lower array refs to 1D -----=//
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//
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// DecomposeArrayRefs -
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// Convert multi-dimensional array references into a sequence of
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// instructions (using getelementpr and cast) so that each instruction
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// has at most one array offset.
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//
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//===---------------------------------------------------------------------===//
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#include "llvm/Transforms/DecomposeArrayRefs.h"
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#include "llvm/iMemory.h"
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#include "llvm/iOther.h"
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#include "llvm/BasicBlock.h"
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#include "llvm/Method.h"
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#include "llvm/Pass.h"
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//
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// This function repeats until we have a one-dim. reference: {
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// // For an N-dim array ref, where N > 1, insert:
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// aptr1 = getElementPtr [N-dim array] * lastPtr, uint firstIndex
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// aptr2 = cast [N-dim-arry] * aptr to [<N-1>-dim-array] *
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// }
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// Then it replaces the original instruction with an equivalent one that
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// uses the last aptr2 generated in the loop and a single index.
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//
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static BasicBlock::reverse_iterator
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decomposeArrayRef(BasicBlock::reverse_iterator& BBI)
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{
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MemAccessInst *memI = cast<MemAccessInst>(*BBI);
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BasicBlock* BB = memI->getParent();
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Value* lastPtr = memI->getPointerOperand();
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vector<Instruction*> newIvec;
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MemAccessInst::const_op_iterator OI = memI->idx_begin();
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for (MemAccessInst::const_op_iterator OE = memI->idx_end(); OI != OE; ++OI)
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{
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if (OI+1 == OE) // skip the last operand
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break;
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assert(isa<PointerType>(lastPtr->getType()));
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vector<Value*> idxVec(1, *OI);
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// The first index does not change the type of the pointer
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// since all pointers are treated as potential arrays (i.e.,
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// int *X is either a scalar X[0] or an array at X[i]).
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//
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const Type* nextPtrType;
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// if (OI == memI->idx_begin())
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// nextPtrType = lastPtr->getType();
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// else
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// {
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const Type* nextArrayType =
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MemAccessInst::getIndexedType(lastPtr->getType(), idxVec,
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/*allowCompositeLeaf*/ true);
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nextPtrType = PointerType::get(cast<SequentialType>(nextArrayType)
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->getElementType());
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// }
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Instruction* gepInst = new GetElementPtrInst(lastPtr, idxVec, "aptr1");
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Instruction* castInst = new CastInst(gepInst, nextPtrType, "aptr2");
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lastPtr = castInst;
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newIvec.push_back(gepInst);
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newIvec.push_back(castInst);
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}
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// Now create a new instruction to replace the original one
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assert(lastPtr != memI->getPointerOperand() && "the above loop did not execute?");
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assert(isa<PointerType>(lastPtr->getType()));
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vector<Value*> idxVec(1, *OI);
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const std::string newInstName = memI->hasName()? memI->getName()
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: string("oneDimRef");
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Instruction* newInst = NULL;
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switch(memI->getOpcode())
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{
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case Instruction::Load:
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newInst = new LoadInst(lastPtr, idxVec /*, newInstName */); break;
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case Instruction::Store:
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newInst = new StoreInst(memI->getOperand(0),
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lastPtr, idxVec /*, newInstName */); break;
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break;
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case Instruction::GetElementPtr:
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newInst = new GetElementPtrInst(lastPtr, idxVec /*, newInstName */); break;
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default:
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assert(0 && "Unrecognized memory access instruction"); break;
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}
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newIvec.push_back(newInst);
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// Replace all uses of the old instruction with the new
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memI->replaceAllUsesWith(newInst);
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// Insert the instructions created in reverse order. insert is destructive
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// so we always have to use the new pointer returned by insert.
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BasicBlock::iterator newI = BBI.base(); // gives ptr to instr. after memI
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--newI; // step back to memI
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for (int i = newIvec.size()-1; i >= 0; i--)
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newI = BB->getInstList().insert(newI, newIvec[i]);
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// Now delete the old instruction and return a pointer to the first new one
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BB->getInstList().remove(memI);
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delete memI;
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BasicBlock::reverse_iterator retI(newI); // reverse ptr to instr before newI
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return --retI; // reverse pointer to newI
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}
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//---------------------------------------------------------------------------
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// Entry point for decomposing multi-dimensional array references
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//---------------------------------------------------------------------------
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static bool
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doDecomposeArrayRefs(Method *M)
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{
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bool changed = false;
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for (Method::iterator BI = M->begin(), BE = M->end(); BI != BE; ++BI)
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for (BasicBlock::reverse_iterator newI, II=(*BI)->rbegin();
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II != (*BI)->rend(); II = ++newI)
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{
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newI = II;
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if (MemAccessInst *memI = dyn_cast<MemAccessInst>(*II))
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{ // Check for a multi-dimensional array access
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const PointerType* ptrType =
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cast<PointerType>(memI->getPointerOperand()->getType());
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if (isa<ArrayType>(ptrType->getElementType()) &&
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memI->getNumOperands() > 1+ memI->getFirstIndexOperandNumber())
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{
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newI = decomposeArrayRef(II);
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changed = true;
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}
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}
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}
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return changed;
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}
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namespace {
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struct DecomposeArrayRefsPass : public MethodPass {
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virtual bool runOnMethod(Method *M) { return doDecomposeArrayRefs(M); }
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};
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}
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Pass *createDecomposeArrayRefsPass() { return new DecomposeArrayRefsPass(); }
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