[PATCH] D143731: [AMDGPU] Break-up large PHIs for DAGISel

[Jay Foad via Phabricator via llvm-commits]

foad added a comment.

> This is because it introduces a need to have a build_vector before copying the PHI value, and that build_vector may have many undef elements. This can cause very high register pressure and abnormal stack usage in some cases.

Do you have any insight into *why* undef elements in build_vector would cause high register pressure? Is there any chance of fixing this elsewhere, by teaching other parts of the compiler to handle undef elements better?


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  https://reviews.llvm.org/D143731/new/

https://reviews.llvm.org/D143731