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gcc flags to disable arithmetic optimisations


gcc flags to disable arithmetic optimisations

By : Steve Bez
Date : September 23 2020, 11:00 PM
wish of those help I do not know such compiler flag.
Maybe you can try to use volatile as a substitute:
code :
unsigned int multiply_by_22(volatile unsigned int a)
{
    return a+a+a+a+a+a+a+a+a+a+a+a+a+a+a+a+a+a+a+a+a+a;
}
push    rbp
mov     rbp, rsp
mov     DWORD PTR [rbp-4], edi
mov     edx, DWORD PTR [rbp-4]
mov     eax, DWORD PTR [rbp-4]
add     edx, eax
mov     eax, DWORD PTR [rbp-4]
add     edx, eax
mov     eax, DWORD PTR [rbp-4]
add     edx, eax
mov     eax, DWORD PTR [rbp-4]
add     edx, eax
mov     eax, DWORD PTR [rbp-4]
add     edx, eax
mov     eax, DWORD PTR [rbp-4]
add     edx, eax
mov     eax, DWORD PTR [rbp-4]
add     edx, eax
mov     eax, DWORD PTR [rbp-4]
add     edx, eax
mov     eax, DWORD PTR [rbp-4]
add     edx, eax
mov     eax, DWORD PTR [rbp-4]
add     edx, eax

etc...


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ARM arithmetic addition and flags update

ARM arithmetic addition and flags update


By : user3259249
Date : March 29 2020, 07:55 AM
I hope this helps . The N flag is always set to the bit 31 of the result. The processor does not care whether you add or subtract signed or unsigned numbers - the resulting bit pattern is the same in both cases. Similarly, the PL/MI suffixes just check for the N flag; they don't care whether you consider numbers signed or unsigned.
Signedness is important for multiplication and division, that's why those instructions have two mnemonics.
XCode 4 - Release Mode Flags, Build Flags, Link Flags

XCode 4 - Release Mode Flags, Build Flags, Link Flags


By : DanPost
Date : March 29 2020, 07:55 AM
python3.x - selective arithmetic based on integer flags

python3.x - selective arithmetic based on integer flags


By : Irshad
Date : March 29 2020, 07:55 AM
Hope that helps I have a list of "Z" and "N" values and am trying to complete simple arithmetic on them (addition and/or subtraction) based on a flag associated with them. For example: , To build on @jonrsharpe's comment:
code :
def apply_operation(Z, N, flag):
    flag_operations = {
        0: None,
        1: (2, -1),
        2: (1, -1),
        3: (2, 2)
    }

    Z += flag_operations[flag][0]
    N += flag_operations[flag][1]

    return (Z, N)

Z = 10
N = 10
flag = 2

Znew, Nnew = apply_operation(Z, N, flag)

print('Z:', Znew, '\tN:', Nnew)
# Z: 11     N: 9
Is it possible to disable gcc/g++ optimisations for specific sections of code?

Is it possible to disable gcc/g++ optimisations for specific sections of code?


By : Mischa Sumrall
Date : March 29 2020, 07:55 AM
This might help you I am compiling some code that works without optimisation but breaks with optimisations enabled. I suspect certain critical sections of the code of being optimised out, resulting in the logic breaking. , You can poke around the GCC documentation. For example:
tasking compiler disable optimisations

tasking compiler disable optimisations


By : smokerg Life Smokerg
Date : March 29 2020, 07:55 AM
like below fixes the issue It seems the TASKING compiler is compatible with GCC with respect to optimization level flags, per this user guide (which is indeed quite old).
For disabling optimizations altogether, select None (-O0) as optimization level in the C/C++ project settings. Note that -O0 is the default optimization level of the Debug configuration.
code :
#pragma optimize 0
void myfunc()  
{
   // function body
}
#pragma endoptimize
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