[Bug target/115726] New: [avr] Wrong code with __memx and local register variables

[gjl at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115726

            Bug ID: 115726
           Summary: [avr] Wrong code with __memx and local register
                    variables
           Product: gcc
           Version: 14.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: gjl at gcc dot gnu.org
  Target Milestone: ---

Created attachment 58548
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=58548&action=edit
GNU-C99 test case

When the result of a read from address-space __memx is forced into some
register, wrong code might be generated.  Reason is that respective insns
expand with clobbers of some hard registers that they will use later on.

With the attached test case for example, with avr-gcc-v14.1 -mmcu=atmega128 -Os
-dp -S the generated assembly is basically like:

xload8_r30:
        ;;      
        mov r24,r30      ;  17  [c=4 l=1]  movqi_insn/0
        ret              ;  20  [c=0 l=1]  return

xload16_r30:
        ;;      
        movw r24,r30     ;  17  [c=4 l=1]  *movhi/0
        ret              ;  20  [c=0 l=1]  return

xload8_r22:
        ;;      
        mov r24,r22      ;  17  [c=4 l=1]  movqi_insn/0
        ret              ;  20  [c=0 l=1]  return

xload16_r22:
        ;;      
        movw r24,r22     ;  17  [c=4 l=1]  *movhi/0
        ret              ;  20  [c=0 l=1]  return

so not a single load is present.