tree 469ebb0ecc933a2a17c8ff2490128a827b5e3dea
parent bceadcbb0ca8e81bf3cec11c74d877461018c9f2
author Sanjay Patel <spatel@rotateright.com> 1558485145 +0000
committer Sanjay Patel <spatel@rotateright.com> 1558485145 +0000

[InstCombine] fold shuffles of insert_subvectors

This should be a valid exception to the general rule of not creating new shuffle masks in IR...
because we already do it. :)
Also, DAG combining/legalization will undo this by widening the shuffle back out if needed.

Explanation for how we already do this: SLP or vector source can create chains of insert/extract
as shown in 1 of the examples from PR16739:
https://godbolt.org/z/NlK7rA
https://bugs.llvm.org/show_bug.cgi?id=16739

And we expect instcombine or DAGCombine to clean that up by creating relatively simple shuffles.

Differential Revision: https://reviews.llvm.org/D62024

llvm-svn: 361338