Jakob Stoklund Olesen 351c8818f2 Handle <undef> operands in TwoAddressInstructionPass.
When the source register to a 2-addr instruction is undefined, there is
no need to attempt any transformations - simply replace the source
register with the destination register.

This also comes up when lowering IMPLICIT_DEF instructions - make sure
the <undef> flag is moved to the new partial register def operand:

  %vreg8<def> = INSERT_SUBREG %vreg9<undef>, %vreg0<kill>, sub_16bit
rewrite undef:
  %vreg8<def> = INSERT_SUBREG %vreg8<undef>, %vreg0<kill>, sub_16bit
convert to:
  %vreg8:sub_16bit<def,read-undef> = COPY %vreg0<kill>

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@159120 91177308-0d34-0410-b5e6-96231b3b80d8
2012-06-25 03:27:12 +00:00
..
2012-04-04 20:33:56 +00:00