Microsoft C Compiler – Is cl.exe a Compiler Driver or a Compiler?

compiler

gccand clang are both known to be compiler drivers. As such, the gcc executable does not compile anything itself. Rather, it calls the compiler (cc1), assembler (as) and linker (ld) with the right flags as needed.

Is this setup true also for the Microsoft C compiler, cl.exe? Is there actually some other executable that does the compilation? I assume that at least the assembling and linking are done by separate executables, since I know that ml.exe (known as MASM) and link.exe exist as separate executables, so cl.exe probably calls them.

Best Answer

So the size of cl.exe is 158 KB. What do you think?

The rest of the MSVC C++ compiler is in various DLLs. The C/C++ compiler driver is officially cl.exe, but many of the driver functions are provided by MsBuild. Other executables include link.exe, lib.exe, ml.exe and bscmake.exe. You can't translate the archictecture or terminology blindly from one product set to another that is completely different.

However, if all you want to do is compile from the command line, cl.exe is the place to go. Details can be found here: https://stackoverflow.com/questions/7865432/command-line-compile-using-cl-exe.

Related Solutions

Compiler Warnings – Understanding and Resolving Them

Some warning are usually safe to ignore but if you do so then over time they'll multiply until that day comes when there are so many that you miss the one warning that really matters because it's hidden in the noise.

Fix warnings immediately (which may include disabling individual rules if you feel that it's never relevant for your context).

Compiler Design – Key Optimizations Explained

The examples in the document you're linking to are (and are intended to be) simplified examples of a particular type of optimization. In the real world, of course, it isn't particularly likely that a developer is going to explicitly write a statement like x = x * 1 so it isn't particularly important that a compiler optimizes that specific statement. On the other hand, there are plenty of more complex transforms of this type that a compiler can implement that would be much more likely to come in handy for actual programs.

The article that you links to talks about how applying algebraic simplification and reassociationis frequently used to complement other optimizations. It can be used to rearrange expressions in order to implement operator strength reduction or constant folding or loop-invariant code motion. A lot of the algebraic transforms that the compiler is going to apply will be with the goal of doing things like collecting all the constant terms of an expression together so they can be factored out, collecting all the loop invariant terms together so that they can be moved outside the loop, etc.

One nice example of this is the "Algebraic Simplifications of Addressing Expressions" section in this word doc.

If you want an example of a case where a very simple transform would be used, imagine something like

[(4*(a + b))/ (4*a)] * c

doing algebraic simplification, you get

[(4*a + 4*b)/ (4*a)] * c
[(4*a)/(4*a) + (4*b)/(4*a)] * c
[1 + b/a] * c
(1*c) + (b/a)*c
c + (b*c)/a

The simplification 1*c = c comes toward the end and only after several other algebraic simplifications and transforms created that expression. Generally, it's not human developers that are writing that, it's the compiler applying other transforms that ultimately rely on the simple rules.

Best Answer

Related Solutions

Compiler Warnings – Understanding and Resolving Them

Compiler Design – Key Optimizations Explained

Related Topic