[llvm] [NFC][PowerPC] Add test to check lanemasks for subregisters. (PR #94363)

[Matt Arsenault via llvm-commits]

================
@@ -0,0 +1,68 @@
+# RUN: llc -mcpu=pwr10 -ppc-track-subreg-liveness -filetype=null  \
+# RUN:   -mtriple=powerpc64le-unknown-linux-gnu -run-pass=greedy,virtregrewriter \
+# RUN:   -debug-only=regalloc -o - %s 2>&1 | FileCheck %s
+# REQUIRES: asserts
+
+# Keep track of all of the lanemasks for various subregsiters.
+#
+# TODO: The mask for %6.sub_vsx1:accrc is the same as the mask for %10.sub_vsx1_then_sub_64:accrc
+#       even though one is a 128 bit register and the other is a 64 bit subregister. This should
----------------
arsenm wrote:

Just because the bitwidths are different doesn't mean this is wrong. They would have the same lane mask if one was half of the other 

https://github.com/llvm/llvm-project/pull/94363