[Bug middle-end/82658] Suboptimal codegen on AVR when right-shifting 8-bit unsigned integers.

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82658

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2017-10-24
          Component|target                      |middle-end
     Ever confirmed|0                           |1

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
Ok.  So the issue is a FE one after all.  With the C FE we have

    volatile unsigned char val;
    unsigned char local = val;
  local = local >> 1;
  val = local;

while the C++ FE preserves the widening from the integer promotion rules:

  <<cleanup_point <<< Unknown tree: expr_stmt
  (void) (local = (unsigned char) val) >>>>>;
  <<cleanup_point <<< Unknown tree: expr_stmt
  (void) (local = (unsigned char) ((int) local >> 1)) >>>>>;
  <<cleanup_point <<< Unknown tree: expr_stmt
  (void) (val = local) >>>>>;

and nothing in the middle-end shortens the right-shift operation.