How to disable compiler optimizations in gcc?

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.

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

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:

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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][1] 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.


[1]:

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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][1] for much more.

[1]:

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Long time ago, but still needed.

info -

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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