I thought I was going crazy when debugging code that worked fine on
cortex m3/4 but created unexpected results on cortex m0.
Turns out that the compiler creates incorrect assembler code for
cortexm0 for div when used with constant expressions. Optimization level
was -O1 and -O-
Take this code:
program divtest;
var
a,b,c,d : word;
begin
a := 64;
b := 8;
c := a div 8; //.LI4
d := a div b; //.LI5
end.
looking at the assembler code it is very evident that no shift
operations are done on cortex m0 (see .LI4). Is this a known issue or
should I create a new one in bugzilla? (Search did not reveal a hit that
looked like a match)
Michael
assembler cortex m0:
.Ll2:
mov r1,#64
ldr r0,.Lj3
strh r1,[r0]
.Ll3:
mov r1,#8
ldr r0,.Lj4
strh r1,[r0]
.Ll4:
ldr r0,.Lj3
ldrh r0,[r0]
uxth r0,r0
ldr r1,.Lj6
strh r0,[r1]
.Ll5:
ldr r0,.Lj3
ldrh r1,[r0]
ldr r0,.Lj4
ldrh r0,[r0]
bl fpc_div_longint
uxth r0,r0
ldr r1,.Lj9
strh r0,[r1]
assembler cortex m4:
.Ll2:
movs r1,#64
ldr r0,.Lj3
strh r1,[r0]
.Ll3:
movs r1,#8
ldr r0,.Lj4
strh r1,[r0]
.Ll4:
ldr r0,.Lj3
ldrh r0,[r0]
asrs r1,r0,#31
add r0,r0,r1,lsr #29
asrs r0,#3
uxth r1,r0
ldr r0,.Lj6
strh r1,[r0]
.Ll5:
ldr r0,.Lj3
ldrh r0,[r0]
ldr r1,.Lj4
ldrh r1,[r1]
sdiv r0,r0,r1
uxth r0,r0
ldr r1,.Lj9
strh r0,[r1]
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