CODEWITHSUNDEEP
llvmllvm-irllvm-c++-api
Darshan Bhat
Darshan Bhat

Reputation: 301

How can I check if a llvm instruction is inside a loop?

I have a filtered set of instructions with in a llvm pass. I want to check if each instruction is a part of any loop ( or sub loops). I know that I can get the parent basic block from an instruction

BasicBlock* bb = aInst->getParent();

But how to check if the instruction / the basic block is part of a loop or not ?

Upvotes: 0

Views: 2041

Answers (1)

droptop
droptop

Reputation: 1671

You can use LoopInfo to find loops in an llvm::Function.

As explained here, you can get the function a given instruction belongs to, compute a dominator tree for that function, and analyze the result with an llvm::LoopInfo::BaseT object.

llvm::DominatorTree DT = llvm::DominatorTree();
DT.recalculate(instr->getFunction());
auto loopInfo = new llvm::LoopInfoBase<llvm::BasicBlock, llvm::Loop>();
loopInfo->releaseMemory();
loopInfo->analyze(DT);

Then you check if instr 's surrounding function contains a loop that contains instr by passing instr and loopInfo to a routine like

bool instrIsInaLoop(llvm::LoopInfoBase<llvm::BasicBlock, llvm::Loop> &loopInfo,
                    llvm::Instruction *instr) {
    for (auto loop : loopInfo) if (instrIsInLoop(loop, instr)) return true;

    return false;
}

with subroutine

bool instrIsInLoop(llvm::Loop *loop, llvm::Instruction *instr) {
    if (loop->contains(instr))
        return true;

    else {
        for (auto subLoop : loop->getSubLoops()) {
            if (instrIsInLoop(loop, instr)) return true;
        }

        return false;
    }

}

Upvotes: 2

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