dark mountain
Hi guys,
I am looking for any reference out there that has more or less covered all kinds of usages on how a certain C/C++ code is going to use which x86_64 assembly instruction. Has anyone compiled something like this or anything close to this available?
I am asking because I recently started to relearn assembly language and I just want to see how the compiler is able to optimize away a lot of code using appropriate instructions.
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quaint estuary
dark mountain
you misunderstand my question. ofcourse i will use godbolt. but i want to knw if people have tried out with various types of code and see what assembly it generates, hopefully covering a major set of x86_64 instructions
limpid sail
the is no direct mapping from C or C++ to assembly.
C and C++ are a lot more than just shorthand notation for assembly.
dark mountain
ofcourse i understand tht. i think people need to read my question well than blindly answering
cold storm
you misunderstand my question. ofcourse i will use godbolt. but i want to knw if...
You can't.
You would need to do this for every optimization setting for every version for every compiler with every possible code-structures which is just unfeasible (mainly because of the "with every possible code-structure" part).
What you can do is type
gcc -Q -O<level> --help=optimizers
```to let it display all the optimizations it supports together with an `[enabled]`/`[disabled]` depending on whether it's on/off for the given optimization level.And then I guess you can look up the optimizations like e.g. if you wanted to know what
-fbranch-count-reg
```does, then you can look it up on the gcc page where it says:
> `-fno-branch-count-reg`
>
> Disable the optimization pass that scans for opportunities to use “decrement and branch” instructions on a count register instead of instruction sequences that decrement a register, compare it against zero, and then branch based upon the result. This option is only meaningful on architectures that support such instructions, which include x86, PowerPC, IA-64 and S/390. Note that the `-fno-branch-count-reg` option doesn’t remove the decrement and branch instructions from the generated instruction stream introduced by other optimization passes.
>
> The default is `-fbranch-count-reg` at -O1 and higher, except for -Og.
If you want to get even more in-depth then I guess you can look through the source code of `gcc` yourself, although I probably wouldn't recommend that.This was extremely helpful. Thank you. I guess you answered me more than what I had in mind. I will check it out.
!solved
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