Add TRI::getCommonSuperRegClass().
This function is a generalization of getMatchingSuperRegClass() to the
symmetric case where both sides are using a sub-register index. It will
find a super-register class and sub-register indexes that make this
diagram commute:
PreA
SuperRC ----------> RCA
| |
| |
PreB | | SubA
| |
| |
V V
RCB ----------> SubRC
SubB
This can be used to coalesce copies like:
%vreg1:sub16 = COPY %vreg2:sub16; GR64:%vreg1, GR32: %vreg2
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@156317
91177308-0d34-0410-b5e6-
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