[AMDGPU] Custom lower INSERT_SUBVECTOR v3, v4, v5, v8
Summary:
Since the changes to introduce vec3 and vec5, INSERT_VECTOR for these
sizes has been marked "expand", which made LegalizeDAG lower it to loads
and stores via a stack slot. The code got optimized a bit later, but the
now-unused stack slot was never deleted.
This commit avoids that problem by custom lowering INSERT_SUBVECTOR into
an EXTRACT_VECTOR_ELT and INSERT_VECTOR_ELT for each element in the
subvector to insert.
V2: Addressed review comments re test.
Differential Revision: https://reviews.llvm.org/D63160
Change-Id: I9e3c13e36f68cfa3431bb9814851cc1f673274e1
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@365148
91177308-0d34-0410-b5e6-
96231b3b80d8
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