Recent posts

#21

Bug reports / Re: Maybe a optimization bug.

Last post by Pelle - April 18, 2026, 05:48:32 PM

A sanity check is missing in the loop idiom optimizer: triangular numbers. This affects all targets. We'll see when I can fix this...

/* The triangular numbers are given by the following formula:
 * Tn = 1 + 2 + 3 + .. + n = (n * (n + 1)) / 2
 */

#22

Bug reports / Re: Maybe a optimization bug.

Last post by Vortex - April 16, 2026, 09:13:41 PM

Disassembling the 32-bit MS COFF object module, building the project as 32-bit console application :

Code Select Expand

_text   SEGMENT PARA PUBLIC 'CODE'

_main   PROC NEAR
        push    eax
        push    offset @152
        call    _printf                               
        add     esp, 8     
        push    5050                                   
        push    offset @154                           
        call    _printf                               
        add     esp, 8                                 
        xor     eax, eax                               
        ret                                           
_main   ENDP

.rdata  SEGMENT DWORD PUBLIC 'CONST'               

@154    label byte
        db 73H, 75H, 6DH, 3DH, 25H, 64H, 0AH, 00H       ; 0000 _ sum=%d..

@152    label byte
        db 69H, 3DH, 25H, 64H, 0AH, 00H                 ; 0008 _ i=%d..

.rdata  ENDS

#23

Bug reports / Re: Maybe a optimization bug.

Last post by TimoVJL - April 16, 2026, 06:04:07 PM

It might be a cdecl problem, so 32-bit programs can use stdcall to avoid it.

#24

Bug reports / Re: Maybe a optimization bug.

Last post by Vortex - April 15, 2026, 10:00:46 PM

The trick i=i-(-1); seems to solve the issue :

Code Select Expand

#include <stdio.h>

int main(void)
{
int i=1, sum=0;
while (i<=100)
{
sum=sum+i;
//i++;
i=i-(-1);
}
printf("i=%d\n",i);
printf("sum=%d\n",sum);
return 0;
}


#25

Bug reports / Re: Maybe a optimization bug.

Last post by John Z - April 15, 2026, 01:57:27 PM

By the way, uncommenting the line below will output the correct result :

Very typical in my experience for the optimization failures.  Sometimes even just a 1 byte change can make it work, or make it fail.

John Z

#26

Add-ins / Re: Line Counter Add-IN

Last post by John Z - April 15, 2026, 01:48:16 PM

Updated DLL for Pelles C Version 14.  No code changes, up-sized the menu icon

John Z

#27

Bug reports / Re: Maybe a optimization bug.

Last post by TimoVJL - April 15, 2026, 12:35:08 PM

For all bug hunters, use pope.exe to check obj-file, as it have internal disassembler.

#28

Bug reports / Re: Maybe a optimization bug.

Last post by Vortex - April 15, 2026, 10:35:59 AM

By the way, uncommenting the line below will output the correct result :

Code Select Expand

printf("i=%d\n",i);

Code Select Expand

#include <stdio.h>

int main(void)
{
    int i=1, sum=0;
    while (i<=100)
    {
        printf("i=%d\n",i);
        sum=sum+i;
        i++;
    }
    printf("i=%d\n",i);
    printf("sum=%d\n",sum);
    return 0;
}

#29

Bug reports / Re: Maybe a optimization bug.

Last post by TimoVJL - April 15, 2026, 07:55:56 AM

from Clang

Code Select Expand

main:
00000000  4883EC28                sub rsp, 28h
00000004  488D0D00000000          lea rcx, [??_C@_05BKKKKIID@i?$DN?$CFd?6?$AA@]
0000000B  BA65000000              mov edx, 65h
00000010  E800000000              call printf
00000015  488D0D00000000          lea rcx, [??_C@_07MJFEPNKA@sum?$DN?$CFd?6?$AA@]
0000001C  BABA130000              mov edx, 13BAh
00000021  E800000000              call printf
00000026  31C0                    xor eax, eax
00000028  4883C428                add rsp, 28h
0000002C  C3                      ret
As Vortex mentioned, this was missing

Code Select Expand

mov edx, 65h

#30

Bug reports / Re: Maybe a optimization bug.

Last post by ander_cc - April 15, 2026, 05:09:23 AM

Hi ander_cc,

A good lesson there similar to a lawyers credo "In Court don't ask a question if you don't already know the answer"  the corollary to teaching, esp programing, is "In classroom don't use an example you haven't tested"    (half kidding you, no offense meant)

But seriously yes there have been, and are issues, with using the optimizations and extensive testing is always needed for these.  I have many programs using optimizations successfully.

Perhaps Pelle can find the cause of this short program, meanwhile

Your program can use optimizations by using this 'fix':

volatile int i=1;

which, as I understand it inhibits the optimizer from making assumptions about i.

John Z

As an aside I would recommend not using any optimizations for teaching.  Optimizing should be performed by the students learning programing.

Cheers,

Yes, It really embarrassed me at that time. I realized I had forgotten to turn off the optimization. Then I explained the reason to my students, and turned off optimization to test the code again, and used gcc -o2 to test the code again.