[PATCH] D60565: [LOOPINFO] Extend Loop object to add utilities to get the loop bounds, step, induction variable, and guard branch.

[Michael Kruse via Phabricator via llvm-commits]

Meinersbur added a comment.

Generally, I'd prefer to use ScalarEvolution over inspecting (and expecting specific) instructions in a loop, whenever possible. Some canonicalization passes are designed for this. In particular, IndVarSimplify used to make canonical loops (i.e. start at zero, increment by one). r133502 introduced `-disable-iv-rewrite` to rely more on ScalarEvolution instead of "opcode/pattern matching" (cite from the commit message). `-enable-iv-rewrite=false` was made the default in r139579 after finding that it slows down many benchmarks. It was completely removed in r153260.

That is, such pattern matching will miss many loops that could have detected with ScalarEvolution or induction-variable rewriting. We could either re-introduce iv-rewrite or make the pattern matching more general (but also more complex) when needed. IMHO, both are less preferable.

ScalarEvolution might not cover all use cases and the LoopInterchange implementation currently is based on finding the induction variable. However, IMHO we should reduced direct uses of the induction variable instead of promoting it to an API.


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