[PATCH] D65164: Define some basic terminology around loops in our documentation

[Johannes Doerfert via Phabricator via llvm-commits]

jdoerfert added a comment.

Some comments, clarifications, and proposed additions.

Thanks for doing this!



================
Comment at: docs/LoopTerminology.rst:23
+  dominance requirement and such are not considered loops.  LoopInfo
+  does not include such cycles.
+
----------------
Could we add something like:
> commonly referred to as irreducible control flow, or irreducible loops.


================
Comment at: docs/LoopTerminology.rst:35
+  outside the loop.  A loop is allowed to be statically infinite, so
+  there need not be any exiting edges.
+
----------------
> * The loop header identifies a loop.
> * Two loops are either disjoint or one is properly contained in the other.
> * LoopInfo organizes loops in a tree structure with an artificial top-level loop in each function that contains all loops not contained in other loops.


================
Comment at: docs/LoopTerminology.rst:48
+contained within the loop.  As such, it is the first one executed if
+the loop executes at all.  
+
----------------
"The basic block", not "a".


================
Comment at: docs/LoopTerminology.rst:63
+may have multiple latch blocks.  A latch block may be conditional or
+unconditional.
+
----------------
Let's make "the source of a backedge" a sentence:
> Thus, q latch block is the source of a backedge.


================
Comment at: docs/LoopTerminology.rst:81
+qualification of the event as a shorthand for when some exiting block
+branches to some exit block. May be zero, or not statically computable.
+
----------------
Why "interesting event happens"?
> The backedge*s* are traversed *without leaving the loop*


================
Comment at: docs/LoopTerminology.rst:89
+width integers (such as LLVM Values or SCEVs), you need to be cautious
+of overflow when converting one to the other.)
+
----------------
Again, we should mention "executed before the loop is left".


================
Comment at: docs/LoopTerminology.rst:90
+of overflow when converting one to the other.)
+
+Loop Simplify Form
----------------
> A basic block can be a exiting block and a latch block at the same time.
> A basic block can also be loop predecessor and a exit block at the same time.

> Irreducible Control Flow - Also known as irreducible loops, are non-loop cycle in the CFG. They differ from the LLVM definition of loops because they do not have a header block, thus no block in the cycle dominates all blocks in the cycle. Warning: LoopInfo does not identify irreducible control flow which means that even in a non-recursive function without loops blocks can be executed multiple times.


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https://reviews.llvm.org/D65164