LDDWRdYQ - Bad machine code: Using an undefined physical register

[dylanmckay]

Found while compiling libcore with the patch from #27 applied

libcore.ll

Reproduction

./bin/llc ~/libcore.ll -O0 -o /dev/null

*** Bad machine code: Using an undefined physical register ***
- function:    _ZN76_$LT$core..char..EscapeDefault$u20$as$u20$core..iter..iterator..Iterator$GT$4next17hd387834b920a4d78E
- basic block: BB#3 bb2 (0x7fb1b59aea38)
- instruction: %R29R28<earlyclobber,def> = LDDWRdYQ
- operand 1:   %R29R28

*** Bad machine code: Using an undefined physical register ***
- function:    _ZN76_$LT$core..char..EscapeDefault$u20$as$u20$core..iter..iterator..Iterator$GT$4next17hd387834b920a4d78E
- basic block: BB#3 bb2 (0x7fb1b59aea38)
- instruction: %R31R30<earlyclobber,def> = LDDWRdYQ
- operand 1:   %R29R28

*** Bad machine code: Using an undefined physical register ***
- function:    _ZN76_$LT$core..char..EscapeDefault$u20$as$u20$core..iter..iterator..Iterator$GT$4next17hd387834b920a4d78E
- basic block: BB#3 bb2 (0x7fb1b59aea38)
- instruction: %R21R20<earlyclobber,def> = LDDWRdYQ
- operand 1:   %R29R28
LLVM ERROR: Found 3 machine code errors.

[dylanmckay]

I've got an upstreamed fix here

[shepmaster]

Cherry-picked llvm-mirror/llvm@f23578f into avr-rust/llvm