#2956 Invalid code for compound assignment operator

[Nikolay]

For testadd function

uint16_t val = 0xFFFF;

uint16_t testadd()
{
    return (val += 1);
}

SDCC produces the next assembly

;   .\Source\main.c: 390: uint16_t testadd()
;   -----------------------------------------
;    function testadd
;   -----------------------------------------
_testadd:
;   .\Source\main.c: 392: return (val += 1);
    ldw x, _val+0
    incw    x
;   .\Source\main.c: 393: }
    ret

Incremented value was not written back to val variable. The same occurs with other compound assignment operators.

;--------------------------------------------------------
; File Created by SDCC : free open source ANSI-C Compiler
; Version 3.9.5 #11479 (MINGW32)
;--------------------------------------------------------
.module main
.optsdcc -mstm8

[Philipp Klaus Krause]

A bug in live-range shortening, moving the return before the assignment to the variable. Subsequent optimizations then removed the now unreachable assignment.

Fixed in [11481].

[Nikolay]

Now it's ok but there's extra y register usage:

; .\Source\main.c: 390: uint16_t testadd()
; -----------------------------------------
; function testadd
; -----------------------------------------
_testadd:
; .\Source\main.c: 392: return (val += 1);
ldw x, _val+0
incw x
ldw y, x
ldw _val+0, y
; .\Source\main.c: 393: }
ret