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

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

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

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

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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 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

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

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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

[c] How to disable compiler optimizations in gcc?

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