[PATCH] D154205: [MachineLICM] Handle subloops

[JinGu Kang via Phabricator via llvm-commits]

jaykang10 added a comment.

In D154205#4494018 <https://reviews.llvm.org/D154205#4494018>, @craig.topper wrote:

> Why do we want to visit inner loops first? Doesn't the algorithm visit all blocks of the inner loops when its on an outer loop anyway?

As you can see on `MachineLoop::isLoopInvariant()`, if the loop contains the definition of MI's operands, the MI is not loop invariant.
Let's see below loop form.

  outer loop:
      definition of operand of below loop invariant code
      inner loop:
          loop invariant code

If we visit only outer loop, the loop invariant code can not be hoisted to outer loop's preheader because its operand's definition is in outer loop.
If we visit inner loop, the loop invariant code can be hoisted to the inner loop's preheader because the inner loop does not contain the definition of the invariant code's operand.
That's the reason why I want to visit the inner loops.
If you feel something wrong, please let me know.


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https://reviews.llvm.org/D154205