why LoopInfoWrapperPass can not detect all the canonical loops?

The original cl code contains 2 canonical loops (start from 0 with stride 1). But the analysis pass LoopInfoWrapperPass only detect one of them, anybody knows why?

The analysis pass LoopInfoWrapperPass is called from a function pass by the following statements:

LoopInfo& LI = getAnalysis().getLoopInfo();

for(LoopInfo::iterator l = LI.begin(), lend = LI.end(); l != lend; ++l){

PHINode* phi = (*l)->getCanonicalInductionVariable();


stencil.cl (683 Bytes)

stencil.ll (5.15 KB)

Hi Dong,

The LI provides iterator for top-level loops. In your test you have only one top-level loop, the other one is nested in it.

Here is what the loop structure looks like for your test:

$ opt -loops -analyze stencil.ll

Printing analysis ‘Natural Loop Information’ for function ‘stencil’:

Loop at depth 1 containing: %for.body,%for.body8.lr.ph,%for.body8,%for.cond.cleanup7.loopexit,%for.cond.cleanup7

Loop at depth 2 containing: %for.body8

There are a number of passes that walk through all loops in a function, you could look at them if you need an example. For example, loop-vectorizer does this:

SmallVector<Loop *, 8> Worklist;
for (Loop *L : *LI)
addInnerLoop(*L, Worklist);

static void addInnerLoop(Loop &L, SmallVectorImpl<Loop *> &V) {

if (L.empty())

return V.push_back(&L);

for (Loop *InnerL : L)

addInnerLoop(*InnerL, V);


Hope this helps!