I came across this RTL on AVR in combine dump (part of va-arg-9.c test)
(set (reg:QI 25 r25 [+1 ])
(subreg:QI (sign_extend:HI (reg:QI 49)) 1))
The sign extension is completely redundant - the upper part of register
is not used elsewhere
- but the RTL remains unchanged through all the optimizers and
sign_extension appears in final code.
Which RTL optimisation should be taking care of this? Propagation?
It would help me look in the right place to understand and perhaps fix
issue.
I suspect the presence of hard register is why it does not get removed.
(the hard register is the function return value)
Andy
