[Bug target/78093] New: [avr] Introduce new variable attribute "absdata" to enable LDS / STS on Reduced Tiny

[gjl at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78093

            Bug ID: 78093
           Summary: [avr] Introduce new variable attribute "absdata" to
                    enable LDS / STS on Reduced Tiny
           Product: gcc
           Version: 7.0
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: gjl at gcc dot gnu.org
  Target Milestone: ---

Currently, the compiler won't use LDS / STS instructions für AVR's reduces Tiny
cores (-mmcu=avrtiny).  The reason is that there are devices in this class
where RAM exceeds the range of absolute addresses 0x0...0xbf.

This PR is about a new variable attribute that allows to express that it is
legitimate to use LDS / STS for specified objects in static storage like in the
following example:

extern char varA __attribute__((absdata));

char get_A (void)
{
  return varA;
}