how to see the optimized code in c

Question

I can examine the optimization using profiler, size of the executable file and time to take for the execution.

I can get the result of the optimization. But I have these questions,

• How to get the optimized C code.
• Which algorithm or method used by C to optimize a code.

Thanks in advance.

Answer 1

Usually the code isn't optimized as C. Usually optimization passes are done long after the C has been converted into some form of intermediate representation that is easier for a compiler to work with in memory. Therefore, a direct answer to your question is that the optimized C code never exists.

Answer 2

The C compiler generally does not produce optimized C and compile that; it generally produces optimized assembly language or machine code.

The closest you can get is probably to compile a file to assembly with no optimization and again with highest optimization, and then compare the assembly output. You will have to have a good grasp of assembly language to do that. If you are using gcc, read about the -S and -O switches for how to do (or not do) this.

Let me clarify some things about the compiler. The algorithms and data structures used by the code you wrote will never be changed by the compiler; the compiler will only be doing things that are exactly equivalent to your C code. That's why it wouldn't usually make sense for the compiler to produce optimized C.

If your goal is to write faster code, then, your best bet is to write better C by using better algorithms and data structures at the C level by carefully using the profiler.

If your goal is just to understand optimization, try Program Optimization and Compiler Optimization on Wikipedia for some general information.

Answer 3

if you understand assembler, you can inspect the assembler generated code by compiler.

Answer 4

you can get an idea of optimization using the option -fdump-tree-optimized with gcc . and you'll get an optimised file. you cannot run the code but using that you can get an idea of optimization . dont forget to include -O2 or -O3 or some other level.

Answer 5

If you're using GCC, use an argument to optimize the code and use --save-temps as an argument. Everyone saying C code isn't optimized as C when compiling with GCC is wrong to an extent. Write a recursive Fibonacci sequence generator in C, and read through the preprocessed code. The aforementioned argument also saves the generated assembly in the directory GCC is called from. If you're more comfortable with Intel-syntax assembly, use -masm=intel as an argument as well.