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    <p>You're trying to do something that is better left to the optimizations of the compiler.</p> <pre><code>int main (void) { int b = 5; int a = b * 2; return a; // return it so we use a and it's not optimized away } </code></pre> <p>gcc -O3 -s t.c </p> <pre><code> .file "t.c" .text .p2align 4,,15 .globl main .type main, @function main: .LFB0: .cfi_startproc movl $10, %eax ret .cfi_endproc .LFE0: .size main, .-main .ident "GCC: (Debian 4.5.0-6) 4.5.1 20100617 (prerelease)" .section .note.GNU-stack,"",@progbits </code></pre> <p>Optimizing compiler will optimize.</p> <p>EDIT: I'm aware that you don't want to hear that the compiler "should" or "usually" does that. However, what you are trying to do is not something that is meant to be done in the C preprocessor; the people who designed the C language and the C preprocessor designed it to work with the preprocessing token as it's basic atom. The CPP is, in many ways, "dumb". This is not a bad thing (in fact, this is in many cases what makes it so useful), but at the end of the day, it is a preprocessor. It preprocesses source files before they are parsed. It preprocesses source files before semantic analysis occurs. It preprocesses source files before the validity of a given source file is checked. I understand that you do not want to hear that this is something that the parser and semantic analyzer should handle or usually does. However, this is the reality of the situation. If you want to design code that is incredibly small, then you should rely on your compiler to do it's job instead of trying to create preprocessor constructs to do the work. Think of it this way: thousands of hours of work went into your compiler, so try to reuse as much of that work as possible!</p>
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    1. COThanks! I like your answer. Seeing the assembly code I can see that the compiler does optimize it. I am not sure if it will do so for higher order functions, and where they involve control logic. But the only way to see is by experimenting so I will go back and check it out for the functions I am interested in.
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    2. COThe best thing to do here is to experiment. If you're using GCC or clang, there's a whole host of ways in which you can inspect what the compiler is doing and what the compiler is not doing. You might even want to check out the clang static analyzer, a very cool tool for examine how C or C++ source code is compiled. Visual Studio also has superb tools for this sort of stuff.
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    3. COhttp://clang-analyzer.llvm.org/ <- link to the clang static analyzer.
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