/** bug2729218.c */ #include /* sdcc appears to compile the following file incorrectly. I have attached the C source code, and the generated assembly code, with some comments that explain the bug. The basic problem is that a memory location is post-incremented, but the register variable that shadows that memory location is NOT increment, and this incorrect value is used in later calculations. I compiled it with these options: sdcc -mmcs51 --model-small --std-sdcc99 --code-loc 0xf000 -c bug.c Here is the "sdcc -v" output: SDCC : mcs51/gbz80/z80/avr/ds390/pic16/pic14/TININative/xa51/ds400/hc08 2.9.1 #5422 (Apr 3 2009) (UNIX) */ struct iglobals { unsigned char rx_byte; unsigned char input_cnt; }; #if !defined(__SDCC_gbz80) && !defined(__SDCC_pdk14) #define ig (*(__idata struct iglobals *) 0xf0) #else struct iglobals ig; #endif unsigned char count; unsigned char do_command(void) { // In the following statement, the post-increment is saved in // memory, but not in the value stored in the r7 register count = ig.input_cnt++; // In the following statement, the value of "input_cnt" stored in // the r7 register is used, but it is wrong (never incremented). return ig.input_cnt; } void testBug(void) { #ifdef __SDCC ig.rx_byte = 0; ig.input_cnt = 1; ASSERT (do_command() == 2); ASSERT (ig.input_cnt == 2); ASSERT (count == 1); #endif }