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"
30 Statistic<> NumAdded("lowerrefs", "# of getelementptr instructions added");
32 struct DecomposePass : public BasicBlockPass {
33 virtual bool runOnBasicBlock(BasicBlock &BB);
35 RegisterOpt<DecomposePass> X("lowerrefs", "Decompose multi-dimensional "
36 "structure/array references");
39 // runOnBasicBlock - Entry point for array or structure references with multiple
42 bool DecomposePass::runOnBasicBlock(BasicBlock &BB) {
44 for (BasicBlock::iterator II = BB.begin(); II != BB.end(); )
45 if (GetElementPtrInst *gep = dyn_cast<GetElementPtrInst>(II++)) // pre-inc
46 if (gep->getNumIndices() >= 2)
47 changed |= DecomposeArrayRef(gep); // always modifies II
51 FunctionPass *llvm::createDecomposeMultiDimRefsPass() {
52 return new DecomposePass();
55 // Function: DecomposeArrayRef()
57 // For any GetElementPtrInst with 2 or more array and structure indices:
59 // opCode CompositeType* P, [uint|ubyte] idx1, ..., [uint|ubyte] idxN
61 // this function generates the following sequence:
63 // ptr1 = getElementPtr P, idx1
64 // ptr2 = getElementPtr ptr1, 0, idx2
66 // ptrN-1 = getElementPtr ptrN-2, 0, idxN-1
67 // opCode ptrN-1, 0, idxN // New-MAI
69 // Then it replaces the original instruction with this sequence,
70 // and replaces all uses of the original instruction with New-MAI.
71 // If idx1 is 0, we simply omit the first getElementPtr instruction.
73 // On return: BBI points to the instruction after the current one
74 // (whether or not *BBI was replaced).
76 // Return value: true if the instruction was replaced; false otherwise.
78 bool llvm::DecomposeArrayRef(GetElementPtrInst* GEP) {
79 if (GEP->getNumIndices() < 2)
82 BasicBlock *BB = GEP->getParent();
83 Value *LastPtr = GEP->getPointerOperand();
84 Instruction *InsertPoint = GEP->getNext(); // Insert before the next insn
86 // Process each index except the last one.
87 User::const_op_iterator OI = GEP->idx_begin(), OE = GEP->idx_end();
88 for (; OI+1 != OE; ++OI) {
89 std::vector<Value*> Indices;
91 // If this is the first index and is 0, skip it and move on!
92 if (OI == GEP->idx_begin()) {
93 if (*OI == ConstantInt::getNullValue((*OI)->getType()))
96 else // Not the first index: include initial [0] to deref the last ptr
97 Indices.push_back(Constant::getNullValue(Type::LongTy));
99 Indices.push_back(*OI);
101 // New Instruction: nextPtr1 = GetElementPtr LastPtr, Indices
102 LastPtr = new GetElementPtrInst(LastPtr, Indices, "ptr1", InsertPoint);
106 // Now create a new instruction to replace the original one
108 const PointerType *PtrTy = cast<PointerType>(LastPtr->getType());
110 // Get the final index vector, including an initial [0] as before.
111 std::vector<Value*> Indices;
112 Indices.push_back(Constant::getNullValue(Type::LongTy));
113 Indices.push_back(*OI);
115 Value *NewVal = new GetElementPtrInst(LastPtr, Indices, GEP->getName(),
118 // Replace all uses of the old instruction with the new
119 GEP->replaceAllUsesWith(NewVal);
121 // Now remove and delete the old instruction...
122 BB->getInstList().erase(GEP);