[llvm-dev] copyPhysReg() with undef source operand (llvm-stress)

[Jonas Paulsson via llvm-dev]

Hi,

I would like some advice on how to lower a COPY in copyPhysReg(), where 
the source operand is undef, because it seems this flag is not available.

With llvm-stress I got (on SystemZ):

B#0: derived from LLVM BB %BB
     Live Ins: %R2D %R4D %R6D
         %vreg14<def> = IMPLICIT_DEF; GR64Bit:%vreg14
         %vreg53<def> = IMPLICIT_DEF; GR128Bit:%vreg53
         %vreg55<def> = LLILL 0; GR64Bit:%vreg55
         %vreg54<def,tied1> = INSERT_SUBREG %vreg53<tied0>, %vreg55, 
subreg_h64; GR128Bit:%vreg54,%vreg53 GR64Bit:%vreg55
         %vreg15<def,tied1> = INSERT_SUBREG %vreg54<tied0>, %vreg14, 
subreg_l64; GR128Bit:%vreg15,%vreg54 GR64Bit:%vreg14

-> Process Implicit Definitions

         %vreg55<def> = LLILL 0; GR64Bit:%vreg55
         %vreg54<def,tied1> = INSERT_SUBREG %vreg53<undef,tied0>, 
%vreg55, subreg_h64; GR128Bit:%vreg54,%vreg53 GR64Bit:%vreg55
         %vreg15<def,tied1> = INSERT_SUBREG %vreg54<tied0>, 
%vreg14<undef>, subreg_l64; GR128Bit:%vreg15,%vreg54 GR64Bit:%vreg14

-> Two-Address instruction pass

         %vreg55<def> = LLILL 0; GR64Bit:%vreg55
         %vreg54:subreg_h64<def,read-undef> = COPY %vreg55<kill>; 
GR128Bit:%vreg54 GR64Bit:%vreg55
         %vreg15<def> = COPY %vreg54<kill>; GR128Bit:%vreg15,%vreg54
         %vreg15:subreg_l64<def> = COPY %vreg14<undef>; GR128Bit:%vreg15 
GR64Bit:%vreg14

-> reg alloc

         %R1D<def> = LLILL 0
         %R12D<def> = COPY %R1D<kill>, %R12Q<imp-def>
         %R13D<def> = COPY %R0D<undef>, %R12Q<imp-use,kill>, %R12Q<imp-def>

-> post-ra pseudo expansion

         %R1D<def> = LLILL 0
         %R12D<def> = LGR %R1D<kill>, %R12Q<imp-def>
         %R13D<def> = LGR %R0D, %R12Q<imp-use,kill>, %R12Q<imp-def>

*** Bad machine code: Using an undefined physical register ***
- function:    autogen_SD13338
- basic block: BB#0 BB (0x4deba88)
- instruction: %R13D<def> = LGR
- operand 1:   %R0D
LLVM ERROR: Found 1 machine code errors.


thanks / Jonas