1 //===- llvm/Transforms/DecomposeMultiDimRefs.cpp - Lower array refs to 1D -===//
3 // The LLVM Compiler Infrastructure
5 // This file was developed by the LLVM research group and is distributed under
6 // the University of Illinois Open Source License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // DecomposeMultiDimRefs - Convert multi-dimensional references consisting of
11 // any combination of 2 or more array and structure indices into a sequence of
12 // instructions (using getelementpr and cast) so that each instruction has at
13 // most one index (except structure references, which need an extra leading
16 //===----------------------------------------------------------------------===//
18 #include "llvm/Transforms/Scalar.h"
19 #include "llvm/DerivedTypes.h"
20 #include "llvm/Constants.h"
21 #include "llvm/Constant.h"
22 #include "llvm/iMemory.h"
23 #include "llvm/iOther.h"
24 #include "llvm/BasicBlock.h"
25 #include "llvm/Pass.h"
26 #include "Support/Statistic.h"
31 Statistic<> NumAdded("lowerrefs", "# of getelementptr instructions added");
33 struct DecomposePass : public BasicBlockPass {
34 virtual bool runOnBasicBlock(BasicBlock &BB);
38 RegisterOpt<DecomposePass> X("lowerrefs", "Decompose multi-dimensional "
39 "structure/array references");
41 // runOnBasicBlock - Entry point for array or structure references with multiple
45 DecomposePass::runOnBasicBlock(BasicBlock &BB)
48 for (BasicBlock::iterator II = BB.begin(); II != BB.end(); )
49 if (GetElementPtrInst *gep = dyn_cast<GetElementPtrInst>(II++)) // pre-inc
50 if (gep->getNumIndices() >= 2)
51 changed |= DecomposeArrayRef(gep); // always modifies II
56 *createDecomposeMultiDimRefsPass()
58 return new DecomposePass();
61 // Function: DecomposeArrayRef()
63 // For any GetElementPtrInst with 2 or more array and structure indices:
65 // opCode CompositeType* P, [uint|ubyte] idx1, ..., [uint|ubyte] idxN
67 // this function generates the foll sequence:
69 // ptr1 = getElementPtr P, idx1
70 // ptr2 = getElementPtr ptr1, 0, idx2
72 // ptrN-1 = getElementPtr ptrN-2, 0, idxN-1
73 // opCode ptrN-1, 0, idxN // New-MAI
75 // Then it replaces the original instruction with this sequence,
76 // and replaces all uses of the original instruction with New-MAI.
77 // If idx1 is 0, we simply omit the first getElementPtr instruction.
79 // On return: BBI points to the instruction after the current one
80 // (whether or not *BBI was replaced).
82 // Return value: true if the instruction was replaced; false otherwise.
85 DecomposeArrayRef(GetElementPtrInst* GEP)
87 if (GEP->getNumIndices() < 2)
90 BasicBlock *BB = GEP->getParent();
91 Value *LastPtr = GEP->getPointerOperand();
92 Instruction *InsertPoint = GEP->getNext(); // Insert before the next insn
94 // The vector of new instructions to be created
95 std::vector<Instruction*> NewInsts;
97 // Process each index except the last one.
98 User::const_op_iterator OI = GEP->idx_begin(), OE = GEP->idx_end();
99 for (; OI+1 != OE; ++OI) {
100 std::vector<Value*> Indices;
102 // If this is the first index and is 0, skip it and move on!
103 if (OI == GEP->idx_begin()) {
104 if (*OI == ConstantInt::getNullValue((*OI)->getType()))
107 else // Not the first index: include initial [0] to deref the last ptr
108 Indices.push_back(Constant::getNullValue(Type::LongTy));
110 Indices.push_back(*OI);
112 // New Instruction: nextPtr1 = GetElementPtr LastPtr, Indices
113 LastPtr = new GetElementPtrInst(LastPtr, Indices, "ptr1", InsertPoint);
117 // Now create a new instruction to replace the original one
119 const PointerType *PtrTy = cast<PointerType>(LastPtr->getType());
121 // Get the final index vector, including an initial [0] as before.
122 std::vector<Value*> Indices;
123 Indices.push_back(Constant::getNullValue(Type::LongTy));
124 Indices.push_back(*OI);
126 Value *NewVal = new GetElementPtrInst(LastPtr, Indices, GEP->getName(),
129 // Replace all uses of the old instruction with the new
130 GEP->replaceAllUsesWith(NewVal);
132 // Now remove and delete the old instruction...
133 BB->getInstList().erase(GEP);
138 } // End llvm namespace