[llvm-commits] [PATCH] Improve codegen for non-constant BUILD_VECTORs on ARM

[James Molloy]

Hi,

Currently if a BUILD_VECTOR is all constants but isn't a constant splat,
a chain of insertelements is created from undef.

However in some cases it may be profitable to start from a different
base; consider "<5, 5, 6, 5>". This would be more profitable to start
from a base of a constant splat of "5", then mutate the third lane to
"6".

The attached patch implements this, by searching for a "dominant"
constant value in the vector. A dominant value is defined as a value
that is present in more than half the lanes.

Please review.

Cheers,

James
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