How can I maximize optimization using gcc?

Question

I made a simple quick sort algorithm using C language, named test.c I'm trying to maximize the optimization, so I use -O3 options like belows.

gcc -S -O3 -o test.s test.c
gcc -S -O3 -o test1.s test.s
gcc -S -O3 -o test2.s test1.s
gcc -S -O3 -o test3.s test2.s
.
.
.

But strange thing happens. The more times I did above procedure, the more number of line assembly get.

I don't know why this happens, because I think that I have to get more optimized assembly file that has smaller number of line as I did above procedure.

If this is not right way, using -O3 only one time is the way of the best optimization?

Thanks

Which version of GCC? My GCC 4.9.2 will not create a new assembly file at all when the source is already in assembly... — thkala
– thkala, Commented May 30, 2015 at 21:13

Jens · Accepted Answer · 2015-05-30 11:28:29Z

1

Most of the gcc optimizations operate on the representation of C source code in an intermediate language. I'm not aware of any optimization specifically operating at the assembler instruction level other than peephole. But that would also be included in -O3.

So yes, -O3 is supposed to be used only once, when turning C source into object files.

answered May 30, 2015 at 11:28

Jens

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