Don't create loop-exiting edges if not necessary

[hhugo]

No description provided.

[vouillon]

By the way, this trick of adding loop-exiting edges does not work when the loop header has no predecessor.

[hhugo]

By the way, this trick of adding loop-exiting edges does not work when the loop header has no predecessor.

I'm guessing this can only happen if the header is the first block of a function

[hhugo]

By the way, this trick of adding loop-exiting edges does not work when the loop header has no predecessor.

I'm guessing this can only happen if the header is the first block of a function

We could prepend an empty block to functions that start with a loop header.