1 //===- llvm/Transforms/DecomposeArrayRefs.cpp - Lower array refs to 1D -----=//
3 // DecomposeArrayRefs -
4 // Convert multi-dimensional array references into a sequence of
5 // instructions (using getelementpr and cast) so that each instruction
6 // has at most one array offset.
8 //===---------------------------------------------------------------------===//
10 #include "llvm/Transforms/DecomposeArrayRefs.h"
11 #include "llvm/iMemory.h"
12 #include "llvm/iOther.h"
13 #include "llvm/BasicBlock.h"
14 #include "llvm/Method.h"
15 #include "llvm/Pass.h"
19 // This function repeats until we have a one-dim. reference: {
20 // // For an N-dim array ref, where N > 1, insert:
21 // aptr1 = getElementPtr [N-dim array] * lastPtr, uint firstIndex
22 // aptr2 = cast [N-dim-arry] * aptr to [<N-1>-dim-array] *
24 // Then it replaces the original instruction with an equivalent one that
25 // uses the last aptr2 generated in the loop and a single index.
27 static BasicBlock::reverse_iterator
28 decomposeArrayRef(BasicBlock::reverse_iterator& BBI)
30 MemAccessInst *memI = cast<MemAccessInst>(*BBI);
31 BasicBlock* BB = memI->getParent();
32 Value* lastPtr = memI->getPointerOperand();
33 vector<Instruction*> newIvec;
35 MemAccessInst::const_op_iterator OI = memI->idx_begin();
36 for (MemAccessInst::const_op_iterator OE = memI->idx_end(); OI != OE; ++OI)
38 if (OI+1 == OE) // skip the last operand
41 assert(isa<PointerType>(lastPtr->getType()));
42 vector<Value*> idxVec(1, *OI);
44 // The first index does not change the type of the pointer
45 // since all pointers are treated as potential arrays (i.e.,
46 // int *X is either a scalar X[0] or an array at X[i]).
48 const Type* nextPtrType;
49 // if (OI == memI->idx_begin())
50 // nextPtrType = lastPtr->getType();
53 const Type* nextArrayType =
54 MemAccessInst::getIndexedType(lastPtr->getType(), idxVec,
55 /*allowCompositeLeaf*/ true);
56 nextPtrType = PointerType::get(cast<SequentialType>(nextArrayType)
60 Instruction* gepInst = new GetElementPtrInst(lastPtr, idxVec, "aptr1");
61 Instruction* castInst = new CastInst(gepInst, nextPtrType, "aptr2");
64 newIvec.push_back(gepInst);
65 newIvec.push_back(castInst);
68 // Now create a new instruction to replace the original one
69 assert(lastPtr != memI->getPointerOperand() && "the above loop did not execute?");
70 assert(isa<PointerType>(lastPtr->getType()));
71 vector<Value*> idxVec(1, *OI);
72 const std::string newInstName = memI->hasName()? memI->getName()
73 : string("oneDimRef");
74 Instruction* newInst = NULL;
76 switch(memI->getOpcode())
78 case Instruction::Load:
79 newInst = new LoadInst(lastPtr, idxVec /*, newInstName */); break;
80 case Instruction::Store:
81 newInst = new StoreInst(memI->getOperand(0),
82 lastPtr, idxVec /*, newInstName */); break;
84 case Instruction::GetElementPtr:
85 newInst = new GetElementPtrInst(lastPtr, idxVec /*, newInstName */); break;
87 assert(0 && "Unrecognized memory access instruction"); break;
90 newIvec.push_back(newInst);
92 // Replace all uses of the old instruction with the new
93 memI->replaceAllUsesWith(newInst);
95 // Insert the instructions created in reverse order. insert is destructive
96 // so we always have to use the new pointer returned by insert.
97 BasicBlock::iterator newI = BBI.base(); // gives ptr to instr. after memI
98 --newI; // step back to memI
99 for (int i = newIvec.size()-1; i >= 0; i--)
100 newI = BB->getInstList().insert(newI, newIvec[i]);
102 // Now delete the old instruction and return a pointer to the first new one
103 BB->getInstList().remove(memI);
106 BasicBlock::reverse_iterator retI(newI); // reverse ptr to instr before newI
107 return --retI; // reverse pointer to newI
111 //---------------------------------------------------------------------------
112 // Entry point for decomposing multi-dimensional array references
113 //---------------------------------------------------------------------------
116 doDecomposeArrayRefs(Method *M)
118 bool changed = false;
120 for (Method::iterator BI = M->begin(), BE = M->end(); BI != BE; ++BI)
121 for (BasicBlock::reverse_iterator newI, II=(*BI)->rbegin();
122 II != (*BI)->rend(); II = ++newI)
125 if (MemAccessInst *memI = dyn_cast<MemAccessInst>(*II))
126 { // Check for a multi-dimensional array access
127 const PointerType* ptrType =
128 cast<PointerType>(memI->getPointerOperand()->getType());
129 if (isa<ArrayType>(ptrType->getElementType()) &&
130 memI->getNumOperands() > 1+ memI->getFirstIndexOperandNumber())
132 newI = decomposeArrayRef(II);
143 struct DecomposeArrayRefsPass : public MethodPass {
144 virtual bool runOnMethod(Method *M) { return doDecomposeArrayRefs(M); }
148 Pass *createDecomposeArrayRefsPass() { return new DecomposeArrayRefsPass(); }