[PATCH] Improve DAG combine pass on certain IR vector patterns

[Fiona Glaser]

> 1. Run your patch through clang-format please. The patch does not follow the LLVM formatting guidelines.

Done, and changed per Mehdi’s suggestions.

> 2. What is the impact of this on arm64 and armv7s generated code? Although the approach makes sense to me, I want to be sure we do not degrade other targets. Note that I do not expect you to run tests if you cannot :).

I don’t think it should even affect any target that doesn’t have canonical vector sizes of both N and 2*N, for a data type of N/2 or smaller. Otherwise the case this patch targets can’t come up.

> 3. What are the runtime performance impact on x86_64, with and without -mavx2?

I’m not sure in general; this affects a few very specific vector constructs that were being pessimized.

> 4. Add a run line for avx  too:
> +; RUN: llc < %s -march=x86-64 -mattr=+avx2 | FileCheck %s

Done.

> 5. Should we use a triple instead of march?

Do triples let you specify particular attributes (AVX, etc?)

Fiona



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