X-Git-Url: http://plrg.eecs.uci.edu/git/?a=blobdiff_plain;f=docs%2FCodingStandards.html;h=d469d6315ecb8be4704b52f524a8f68e069ceed7;hb=65797b83a959e580e2bf293c93091dbaf5a820b5;hp=83ca1dc24ad635d3cda6834367215e0dfc603903;hpb=f7235cde69c7017aecbc6609ee3db2fc81ad2668;p=oota-llvm.git diff --git a/docs/CodingStandards.html b/docs/CodingStandards.html index 83ca1dc24ad..d469d6315ec 100644 --- a/docs/CodingStandards.html +++ b/docs/CodingStandards.html @@ -14,6 +14,7 @@
  1. Commenting
  2. Comment Formatting +
  3. #include Style
  4. Source Code Width
  5. Use Spaces Instead of Tabs
  6. Indent Code Consistently @@ -52,14 +53,24 @@

    Commenting

      -Comments are one critical part of readability and maintainability. Everyone knows they should comment, so should you. :) Although we all should probably comment our code more than we do, there are a few very critical places that documentation is very useful:

      +Comments are one critical part of readability and maintainability. Everyone +knows they should comment, so should you. :) Although we all should probably +comment our code more than we do, there are a few very critical places that +documentation is very useful:

      1. File Headers

        2. -Every source file should have a header on it that describes the basic purpose of the file. If a file does not have a header, it should not be checked into CVS. Most source trees will probably have a standard file header format. The standard format for the LLVM source tree looks like this:

        +Every source file should have a header on it that describes the basic purpose of +the file. If a file does not have a header, it should not be checked into CVS. +Most source trees will probably have a standard file header format. The +standard format for the LLVM source tree looks like this:

        -//===-- llvm/Instruction.h - Instruction class definition --------*- C++ -*--=//
+//===-- llvm/Instruction.h - Instruction class definition -------*- C++ -*-===//
 //
 // This file contains the declaration of the Instruction class, which is the
 // base class for all of the VM instructions.
@@ -92,36 +109,92 @@ Every source file should have a header on it that describes the basic purpose of
 //===----------------------------------------------------------------------===//
        -A few things to note about this particular format. The "-*- C++ -*-" string on the first line is there to tell Emacs that the source file is a C++ file, not a C file (Emacs assumes .h files are C files by default [Note that tag this is not neccesary in .cpp files]). The name of the file is also on the first line, along with a very short description of the purpose of the file. This is important when printing out code and flipping though lots of pages.

        +A few things to note about this particular format. The "-*- C++ -*-" +string on the first line is there to tell Emacs that the source file is a C++ +file, not a C file (Emacs assumes .h files are C files by default [Note that tag +this is not necessary in .cpp files]). The name of the file is also on the +first line, along with a very short description of the purpose of the file. +This is important when printing out code and flipping though lots of pages.

        -The main body of the description does not have to be very long in most cases. Here it's only two lines. If an algorithm is being implemented or something tricky is going on, a reference to the paper where it is published should be included, as well as any notes or "gotchas" in the code to watch out for.

        +The main body of the description does not have to be very long in most cases. +Here it's only two lines. If an algorithm is being implemented or something +tricky is going on, a reference to the paper where it is published should be +included, as well as any notes or "gotchas" in the code to watch out for.

      2. Class overviews

        3. -Classes are one fundemental part of a good object oriented design. As such, a class definition should have a comment block that explains what the class is used for... if it's not obvious. If it's so completely obvious your grandma could figure it out, it's probably safe to leave it out. Naming classes something sane goes a long ways towards avoiding writing documentation. :)

        +Classes are one fundemental part of a good object oriented design. As such, a +class definition should have a comment block that explains what the class is +used for... if it's not obvious. If it's so completely obvious your grandma +could figure it out, it's probably safe to leave it out. Naming classes +something sane goes a long ways towards avoiding writing documentation. :)

      3. Method information

        4. -Methods defined in a class (as well as any global functions) should also be documented properly. A quick note about what it does any a description of the borderline behaviour is all that is neccesary here (unless something particularly tricky or insideous is going on). The hope is that people can figure out how to use your interfaces without reading the code itself... that is the goal metric.

        +Methods defined in a class (as well as any global functions) should also be +documented properly. A quick note about what it does any a description of the +borderline behaviour is all that is necessary here (unless something +particularly tricky or insideous is going on). The hope is that people can +figure out how to use your interfaces without reading the code itself... that is +the goal metric.

        -Good things to talk about here are what happens when something unexpected happens: does the method return null? Abort? Format your hard disk?

        +Good things to talk about here are what happens when something unexpected +happens: does the method return null? Abort? Format your hard disk?

    Comment Formatting

      -In general, prefer C++ style (//) comments. They take less space, require less typing, don't have nesting problems, etc. There are a few cases when it is useful to use C style (/* */) comments however:

      +In general, prefer C++ style (//) comments. They take less space, +require less typing, don't have nesting problems, etc. There are a few cases +when it is useful to use C style (/* */) comments however:

        -
      1. When writing a C code: Obviously if you are writing C code, use C style comments. :) +
      2. When writing a C code: Obviously if you are writing C code, use C style +comments. :)
      3. When writing a header file that may be #included by a C source file. -
      4. When writing a source file that is used by a tool that only accepts C style comments. +
      5. When writing a source file that is used by a tool that only accepts C style +comments.

      -To comment out a large block of code, use #if 0 and #endif. These nest properly and are better behaved in general than C style comments.

      +To comment out a large block of code, use #if 0 and #endif. +These nest properly and are better behaved in general than C style comments.

      + + +

    #include Style

    Use Spaces Instead of Tabs

    Indent Code Consistently

      -Okay, your first year of programming you were told that indentation is important. If you didn't believe and internalize this then, now is the time. Just do it.

      +Okay, your first year of programming you were told that indentation is +important. If you didn't believe and internalize this then, now is the time. +Just do it.

      @@ -155,9 +238,17 @@ Okay, your first year of programming you were told that indentation is important

    Treat Compiler Warnings Like Errors

      -If your code has compiler warnings in it, something is wrong: you aren't casting values correctly, your have "questionable" constructs in your code, or you are doing something legitimately wrong. Compiler warnings can cover up legitimate errors in output and make dealing with a translation unit difficult.

      +If your code has compiler warnings in it, something is wrong: you aren't casting +values correctly, your have "questionable" constructs in your code, or you are +doing something legitimately wrong. Compiler warnings can cover up legitimate +errors in output and make dealing with a translation unit difficult.

      -It is not possible to prevent all warnings from all compilers, nor is it desirable. Instead, pick a standard compiler (like gcc) that provides a good thorough set of warnings, and stick to them. At least in the case of gcc, it is possible to work around any spurious errors by changing the syntax of the code slightly. For example, an warning that annoys me occurs when I write code like this:

      +It is not possible to prevent all warnings from all compilers, nor is it +desirable. Instead, pick a standard compiler (like gcc) that provides +a good thorough set of warnings, and stick to them. At least in the case of +gcc, it is possible to work around any spurious errors by changing the +syntax of the code slightly. For example, an warning that annoys me occurs when +I write code like this:

         if (V = getValue()) {
@@ -165,7 +256,10 @@ It is not possible to prevent all warnings from all compilers, nor is it desirab
   }

      -gcc will warn me that I probably want to use the == operator, and that I probably mistyped it. In most cases, I haven't, and I really don't want the spurious errors. To fix this particular problem, I rewrite the code like this:

      +gcc will warn me that I probably want to use the == operator, +and that I probably mistyped it. In most cases, I haven't, and I really don't +want the spurious errors. To fix this particular problem, I rewrite the code +like this:

         if ((V = getValue())) {
@@ -173,33 +267,53 @@ It is not possible to prevent all warnings from all compilers, nor is it desirab
   }

      -...which shuts gcc up. Any gcc warning that annoys you can be fixed by massaging the code appropriately.

      +...which shuts gcc up. Any gcc warning that annoys you can be +fixed by massaging the code appropriately.

      -These are the gcc warnings that I prefer to enable: -Wall -Winline -W -Wwrite-strings -Wno-unused

      +These are the gcc warnings that I prefer to enable: -Wall -Winline +-W -Wwrite-strings -Wno-unused

    Which C++ features can I use?

      -Compilers are finally catching up to the C++ standard. Most compilers implement most features, so you can use just about any features that you would like. In the LLVM source tree, I have chosen to not use these features:

      +Compilers are finally catching up to the C++ standard. Most compilers implement +most features, so you can use just about any features that you would like. In +the LLVM source tree, I have chosen to not use these features:

        -
      1. Exceptions: Exceptions are very useful for error reporting and handling exceptional conditions. I do not use them in LLVM because they do have an associated performance impact (by restricting restructuring of code), and parts of LLVM are designed for performance critical purposes.

        - -Just like most of the rules in this document, this isn't a hard and fast requirement. Exceptions are used in the Parser, because it simplifies error reporting significantly, and the LLVM parser is not at all in the critical path.

        - -

      2. RTTI: RTTI has a large cost in terms of executable size, and compilers are not yet very good at stomping out "dead" class information blocks. Because of this, typeinfo and dynamic cast are not used. +
      3. Exceptions: Exceptions are very useful for error reporting and handling +exceptional conditions. I do not use them in LLVM because they do have an +associated performance impact (by restricting restructuring of code), and parts +of LLVM are designed for performance critical purposes.

        + +Just like most of the rules in this document, this isn't a hard and fast +requirement. Exceptions are used in the Parser, because it simplifies error +reporting significantly, and the LLVM parser is not at all in the +critical path.

        + +

      4. RTTI: RTTI has a large cost in terms of executable size, and compilers are +not yet very good at stomping out "dead" class information blocks. Because of +this, typeinfo and dynamic cast are not used.

      -Other features, such as templates (without partial specialization) can be used freely. The general goal is to have clear, consise, performant code... if a technique assists with that then use it.

      +Other features, such as templates (without partial specialization) can be used +freely. The general goal is to have clear, consise, performant code... if a +technique assists with that then use it.

    Write Portable Code

      -In almost all cases, it is possible and within reason to write completely portable code. If there are cases where it isn't possible to write portable code, isolate it behind a well defined (and well documented) interface.

      +In almost all cases, it is possible and within reason to write completely +portable code. If there are cases where it isn't possible to write portable +code, isolate it behind a well defined (and well documented) interface.

      -In practice, this means that you shouldn't assume much about the host compiler, including its support for "high tech" features like partial specialization of templates. In fact, Visual C++ 6 could be an important target for our work in the future, and we don't want to have to rewrite all of our code to support it.

      +In practice, this means that you shouldn't assume much about the host compiler, +including its support for "high tech" features like partial specialization of +templates. In fact, Visual C++ 6 could be an important target for our work in +the future, and we don't want to have to rewrite all of our code to support +it.

      @@ -219,33 +333,65 @@ In practice, this means that you shouldn't assume much about the host compiler,

    A Public Header File is a Module

    #include as Little as Possible

      -#include hurts compile time performance. Don't do it unless you have to, especially in header files.

      +#include hurts compile time performance. Don't do it unless you have +to, especially in header files.

      -But wait, sometimes you need to have the definition of a class to use it, or to inherit from it. In these cases go ahead and #include that header file. Be aware however that there are many cases where you don't need to have the full definition of a class. If you are using a pointer or reference to a class, you don't need the header file. If you are simply returning a class instance from a prototyped function or method, you don't need it. In fact, for most cases, you simply don't need the definition of a class... and not #include'ing speeds up compilation.

      +But wait, sometimes you need to have the definition of a class to use it, or to +inherit from it. In these cases go ahead and #include that header file. Be +aware however that there are many cases where you don't need to have the full +definition of a class. If you are using a pointer or reference to a class, you +don't need the header file. If you are simply returning a class instance from a +prototyped function or method, you don't need it. In fact, for most cases, you +simply don't need the definition of a class... and not #include'ing +speeds up compilation.

      -It is easy to try to go too overboard on this recommendation, however. You must include all of the header files that you are using, either directly or indirectly (through another header file). To make sure that you don't accidently forget to include a header file in your module header, make sure to include your module header first in the implementation file (as mentioned above). This way there won't be any hidden dependencies that you'll find out about later...

      +It is easy to try to go too overboard on this recommendation, however. You +must include all of the header files that you are using, either directly +or indirectly (through another header file). To make sure that you don't +accidently forget to include a header file in your module header, make sure to +include your module header first in the implementation file (as mentioned +above). This way there won't be any hidden dependencies that you'll find out +about later...

    Keep "internal" Headers Private

      -Many modules have a complex implementation that causes them to use more than one implementation (.cpp) file. It is often tempting to put the internal communication interface (helper classes, extra functions, etc) in the public module header file. Don't do this. :)

      +Many modules have a complex implementation that causes them to use more than one +implementation (.cpp) file. It is often tempting to put the internal +communication interface (helper classes, extra functions, etc) in the public +module header file. Don't do this. :)

      -If you really need to do something like this, put a private header file in the same directory as the source files, and include it locally. This ensures that your private interface remains private and undisturbed by outsiders.

      +If you really need to do something like this, put a private header file in the +same directory as the source files, and include it locally. This ensures that +your private interface remains private and undisturbed by outsiders.

      -Note however, that it's okay to put extra implementation methods a public class itself... just make them private (or protected), and all is well.

      +Note however, that it's okay to put extra implementation methods a public class +itself... just make them private (or protected), and all is well.

      @@ -257,9 +403,17 @@ Note however, that it's okay to put extra implementation methods a public class

    Assert Liberally

      -Use the "assert" function to its fullest. Check all of your preconditions and assumptions, you never know when a bug (not neccesarily even yours) might be caught early by an assertion, which reduces debugging time dramatically. The "assert.h" header file is probably already included by the header files you are using, so it doesn't cost anything to use it.

      +Use the "assert" function to its fullest. Check all of your +preconditions and assumptions, you never know when a bug (not neccesarily even +yours) might be caught early by an assertion, which reduces debugging time +dramatically. The "<cassert>" header file is probably already +included by the header files you are using, so it doesn't cost anything to use +it.

      -To further assist with debugging, make sure to put some kind of error message in the assertion statement (which is printed if the assertion is tripped). This helps the poor debugging make sense of why an assertion is being made and enforced, and hopefully what to do about it. Here is one complete example:

      +To further assist with debugging, make sure to put some kind of error message in +the assertion statement (which is printed if the assertion is tripped). This +helps the poor debugging make sense of why an assertion is being made and +enforced, and hopefully what to do about it. Here is one complete example:

         inline Value *getOperand(unsigned i) { 
@@ -288,15 +442,24 @@ You get the idea...

    Prefer Preincrement

      -Hard fast rule: Preincrement (++X) may be no slower than postincrement (X++) and could very well be a lot faster than it. Use preincrementation whenever possible.

      +Hard fast rule: Preincrement (++X) may be no slower than postincrement (X++) and +could very well be a lot faster than it. Use preincrementation whenever +possible.

      -The semantics of postincrement include making a copy of the value being incremented, returning it, and then preincrementing the "work value". For primitive types, this isn't a big deal... but for iterators, it can be a huge issue (for example, some iterators contains stack and set objects in them... copying an iterator could invoke the copy ctor's of these as well). In general, get in the habit of always using preincrement, and you won't have a problem.

      +The semantics of postincrement include making a copy of the value being +incremented, returning it, and then preincrementing the "work value". For +primitive types, this isn't a big deal... but for iterators, it can be a huge +issue (for example, some iterators contains stack and set objects in them... +copying an iterator could invoke the copy ctor's of these as well). In general, +get in the habit of always using preincrement, and you won't have a problem.

    Avoid endl

      -The endl modifier, when used with iostreams outputs a newline to the output stream specified. In addition to doing this, however, it also flushes the output stream. In other words, these are equivalent:

      +The endl modifier, when used with iostreams outputs a newline to the +output stream specified. In addition to doing this, however, it also flushes +the output stream. In other words, these are equivalent:

         cout << endl;
@@ -309,9 +472,15 @@ Most of the time, you probably have no reason to flush the output stream, so it'

    Exploit C++ to its Fullest