How to disable compiler optimizations in gcc

Question

I am trying to learn assembly language  I have searched and found how to disassemble a  c file but I think it produces some optimized version of the program  Is there any way so that I can see the exact assembly code which corresponds to my C file

User · Answer

To test without copy elision and see you copy/move constructors/operators in action add "-fno-elide-constructors".

Even with no optimizations (-O0 ), GCC and Clang will still do copy elision, which has the effect of skipping copy/move constructors in some cases. See this question for the details about copy elision.

However, in Clang 3.4 it does trigger a bug (an invalid temporary object without calling constructor), which is fixed in 3.5.

User · Answer

You can disable optimizations if you pass -O0 with the gcc command-line   E g  to turn a  C file into a  S file call   gcc -O0 -S test c

User · Answer

For gcc you want to omit any -O1 -O2 or -O3 options passed to the compiler or if you already have them you can append the -O0 option to turn it off again   It might also help you to add -g for debug so that you can see the c source and disassembled machine code in your debugger   See also  http   sourceware org gdb onlinedocs gdb Optimized-Code html

User · Answer

Use the command-line option -O0  - capital o  zero   to disable optimization  and -S to get assembly file  Look here to see more gcc command-line options

User · Answer

Long time ago  but still needed   info - https   gcc gnu org onlinedocs gcc Optimize-Options html list - gcc -Q --help optimizers test c   grep enabled disable as many as you like with    gcc   -fno-web   -Q --help optimizers test c   grep enabled

User · Answer

The gcc option -O enables different levels of optimization  Use -O0 to disable them and use -S to output assembly  -O3 is the highest level of optimization   Starting with gcc 4 8 the optimization level -Og is available  It enables optimizations that do not interfere with debugging and is the recommended default for the standard edit-compile-debug cycle   To change the dialect of the assembly to either intel or att use -masm intel or -masm att   You can also enable certain optimizations manually with -fname   Have a look at the gcc manual for much more

User · Answer

You can also control optimisations internally with  pragma GCC push options   pragma GCC push options     pragma GCC optimize   unroll-loops                 code here         pragma GCC pop options

[c] How to disable compiler optimizations in gcc?

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