Мож avr/io.h включить нужно?
32:dummy.c **** global_var = SP;
132 .LM13:
133 0078 8DB7 in r24,93-0x20
134 007a 9EB7 in r25,(93)+1-0x20
135 007c 9093 0000 sts (global_var)+1,r25
136 0080 8093 0000 sts global_var,r24
33:dummy.c **** SP = global_var;
138 .LM14:
139 0084 8091 0000 lds r24,global_var
140 0088 9091 0000 lds r25,(global_var)+1
141 008c 9EBF out (93)+1-0x20,r25
142 008e 8DBF out 93-0x20,r24