Utility to print all the basic blocks of a loop.

[hiraditya]

Summary

Useful in debugging.

[sanjoy]

llvm/include/llvm/Analysis/LoopInfoImpl.h

339 ↗

(On Diff #65541)

Not sure if this needs to be a completely separate method -- why not just pass in a verbose flag to print?

349 ↗

(On Diff #65541)

Hm, just noticed that this is misleading both here and in the print method above -- if the loop has multiple latches, we won't tag any blocks as <latch>. This should be fixed (we need a isLoopLatch helper like we have isLoopExiting). @hiraditya - do you mind fixing this in a later change? If you won't be able to get to it, please let me know and I'll do it.

[hiraditya]

llvm/include/llvm/Analysis/LoopInfoImpl.h

339 ↗

(On Diff #65541)

Okay, I'll push the patch with just another parameter to print.

349 ↗

(On Diff #65541)

I can do that in a separate patch. Thanks for the pointer.

[hiraditya]

Addresssed comments of Sanjoy.

[sanjoy]

LGTM with comments inline.

However: if it isn't too much extra work, can I ask you to please land
the Verbose flag in a separate change from the isLoopLatch change?
If that's too much extra work, don't bother, since these are low risk
changes.

llvm/include/llvm/Analysis/LoopInfo.h

171 ↗

(On Diff #65579)

Don't repeat function names in new doxygen comments.

176 ↗

(On Diff #65579)

I'd do this slightly differently. I'd have the precondition be that
BB belongs to the loop (and start with an assert(contains(BB))),
and have the body just be a:

auto PredBegin = ...;
auto PredEnd = ...;
return std::find(BB, PredBegin, PredEnd) != PredEnd;

llvm/lib/Analysis/LoopInfo.cpp

392 ↗

(On Diff #65579)

Add a /*Verbose=*/ before true and /*Depth=*/ before 0.

[sebpop]

In D22817#496596, @sanjoy wrote:

LGTM with comments inline.

However: if it isn't too much extra work, can I ask you to please land
the Verbose flag in a separate change from the isLoopLatch change?
If that's too much extra work, don't bother, since these are low risk
changes.

Split in two patches and addressed all last comments:
https://reviews.llvm.org/rL276837
https://reviews.llvm.org/rL276838

Thanks Sanjoy for your review.

llvm/trunk/include/llvm/Analysis/LoopInfo.h

for (typename BlockTraits::ChildIteratorType SI =
          BlockTraits::child_begin(BB),
          SE = BlockTraits::child_end(BB); SI != SE; ++SI) {
       if (!contains(*SI))
         return true;
     }
     return false;
   }
 
+  /// Returns true if \p BB is a loop-latch.
+  /// A latch block is a block that contains a branch back to the header.
+  /// This function is useful when there are multiple latches in a loop
+  /// because \fn getLoopLatch will return nullptr in that case.
+  bool isLoopLatch(const BlockT *BB) const {
+    assert(contains(BB) && "block does not belong to the loop");
+
+    BlockT *Header = getHeader();
+    auto PredBegin = GraphTraits<Inverse<BlockT*> >::child_begin(Header);
+    auto PredEnd = GraphTraits<Inverse<BlockT*> >::child_end(Header);
+    return std::find(PredBegin, PredEnd, BB) != PredEnd;
+  }
+
   /// Calculate the number of back edges to the loop header.
   unsigned getNumBackEdges() const {
     unsigned NumBackEdges = 0;
     BlockT *H = getHeader();
 
     typedef GraphTraits<Inverse<BlockT*> > InvBlockTraits;
     for (typename InvBlockTraits::ChildIteratorType I =
          InvBlockTraits::child_begin(H),