Jakob Stoklund Olesen 6b556f824d 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>

llvm-svn: 159120

2012-06-25 03:27:12 +00:00

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