[PATCH] D77058: [Clang] Add llvm.loop.unroll.disable to loops with -fno-unroll-loops.

Tue Apr 7 04:49:49 PDT 2020

Meinersbur added a comment.

LGTM, since it continues current practice. `optnone` will always be the more annoying.

In D77058#1964714 <https://reviews.llvm.org/D77058#1964714>, @fhahn wrote:

> IIUC we don't need a patch similar like this one for optnone, as it already gets added to the function attributes (for -O0) and has an option to disable adding it (-Xclang -disable-O0-optnone) on a per-TU basis.

My question was the other way around: Do we need something like `-xclang -disable-fno-unroll-loops-metadata`.

I documented for Polly <http://polly.llvm.org/docs/UsingPollyWithClang.html#isolate-the-polly-passes> how to get the IR for further processing. There is `clang -Xclang -disable-O0-optnone` and another is `clang -O1 -Xclang -disable-llvm-passes`. Both avoid the optnone attribute, but will yield different results with `-fno-unroll-loops`. Which is the 'correct' way?

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https://reviews.llvm.org/D77058