[fpc-devel] div creates wrong results on cortexm0

[Jeppe Johansen]

Does the attached patch work?

On 1/26/19 12:20 PM, Michael Ring wrote:
> 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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