[Bug rtl-optimization/117910] New: [avr][lra] Wrong code with -mlra in cmpdi-1.c

[gjl at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=117910

            Bug ID: 117910
           Summary: [avr][lra] Wrong code with -mlra in cmpdi-1.c
           Product: gcc
           Version: 15.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: rtl-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: gjl at gcc dot gnu.org
  Target Milestone: ---

Created attachment 59782
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=59782&action=edit
Reduced C test case from cmpdi-1.c

There is yet another fail with -mlra with the attached cmpdi-1.c that produces
wrong code.

$avr-gcc -mmcu=atmega128 -dumpbase "" -save-temps -dp -Os -o cmpdi-1.elf -mlra
-fverbose-asm cmpdi-1.c

Notice the following load / stores involving Y+12 and X+12 in cmpdi-1.s:

   std Y+13,r25  ;  %sfp, _51    ;  685 [c=4 l=2]  *movhi/3
   std Y+12,r24  ;  %sfp, _51
...
   std Y+12,r25  ;  %sfp, tmp162 ;  588 [c=4 l=2]  *movhi/3
   std Y+11,r24  ;  %sfp, tmp162
...
   std Y+11,r24  ;  %sfp, arg1   ;  615 [c=4 l=1]  movqi_insn/2
...
   ldd r16,Y+11  ; , %sfp        ;  640 [c=4 l=1]  movqi_insn/3
...
   std Y+12,r9   ;  %sfp, res    ;  439 [c=4 l=2]  *movhi/3
   std Y+11,r8   ;  %sfp, res
...
   ldd r24,Y+12  ;  _51, %sfp    ;  435 [c=8 l=2]  *movhi/2
   ldd r25,Y+13  ;  _51, %sfp

So it seems LRA is trampling some values / is using wrong offsets.

Target: avr
Configured with: ../../source/gcc-master/configure --target=avr --disable-nls
--with-dwarf2 --with-gnu-as --with-gnu-ld --with-long-double=64
--enable-languages=c,c++
Thread model: single
Supported LTO compression algorithms: zlib
gcc version 15.0.0 20241203 (experimental) (GCC)