[PPC] Fix PR24216: Don't generate splat for misaligned shuffle mask
Given certain shuffle-vector masks, LLVM emits splat instructions
which splat the wrong bytes from the source register. The issue is
that the function PPC::isSplatShuffleMask() in PPCISelLowering.cpp
does not ensure that the splat pattern found is requesting bytes that
are aligned on an EltSize boundary. This patch detects this situation
as not a valid splat mask, resulting in a permute being generated
instead of a splat.
Patch and test case by Tyler Kenney, cleaned up a bit by me.
This is a simple bug fix that would be good to incorporate into 3.7.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@243519 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed