... and each category should be sorted by name.
+and each category should be sorted by name.
The "Main Module Header" file applies to .cpp files which implement an interface defined by a .h file. This #include @@ -292,7 +292,7 @@ value and would be detrimental to printing out code. Also many other projects have standardized on 80 columns, so some people have already configured their editors for it (vs something else, like 90 columns).
-This is one of many contentious issues in coding standards, but is not up +
This is one of many contentious issues in coding standards, but it is not up for debate.
@@ -306,12 +306,12 @@ for debate.In all cases, prefer spaces to tabs in source files. People have different preferred indentation levels, and different styles of indentation that they -like... this is fine. What isn't is that different editors/viewers expand tabs -out to different tab stops. This can cause your code to look completely +like; this is fine. What isn't fine is that different editors/viewers expand +tabs out to different tab stops. This can cause your code to look completely unreadable, and it is not worth dealing with.
As always, follow the Golden Rule above: follow the -style of existing code if your are modifying and extending it. If you like four +style of existing code if you are modifying and extending it. If you like four spaces of indentation, DO NOT do that in the middle of a chunk of code with two spaces of indentation. Also, do not reindent a whole source file: it makes for incredible diffs that are absolutely worthless.
@@ -345,17 +345,17 @@ Just do it.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 +
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 +a good thorough set of warnings, and stick to it. 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 +syntax of the code slightly. For example, a warning that annoys me occurs when I write code like this:
...which shuts gcc up. Any gcc warning that annoys you can +
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 ++
LLVM does not use RTTI (e.g. dynamic_cast<>) or exceptions, in an -effort to reduce code and executable size. These two language features violate -the general C++ principle of "you only pay for what you use", causing executable -bloat even if exceptions are never used in a code base, or if RTTI is never used -for a class. Because of this, we turn them off globally in the code. -
+In an effort to reduce code and executable size, LLVM does not use RTTI +(e.g. dynamic_cast<>) or exceptions. These two language features +violate the general C++ principle of "you only pay for what you use", +causing executable bloat even if exceptions are never used in the code base, or +if RTTI is never used for a class. Because of this, we turn them off globally +in the code.
--That said, LLVM does make extensive use of a hand-rolled form of RTTI that use -templates like isa<>, cast<>, -and dyn_cast<>. This form of RTTI is opt-in and can be added to any -class. It is also substantially more efficient than dynamic_cast<>. -
+That said, LLVM does make extensive use of a hand-rolled form of RTTI that +use templates like isa<>, +cast<>, and dyn_cast<>. This form of RTTI is +opt-in and can be added to any class. It is also substantially more efficient +than dynamic_cast<>.
So, the rule for LLVM is to always use the class keyword, unless -all members are public and the type is a C++ "POD" type, in which case -struct is allowed.
+all members are public and the type is a C++ +POD type, in +which case struct is allowed. @@ -473,18 +478,18 @@ declare the symbol. This can lead to problems at link time.C++ doesn't do too well in the modularity department. There is no real encapsulation or data hiding (unless you use expensive protocol classes), but it is what we have to work with. When you write a public header file (in the LLVM -source tree, they live in the top level "include" directory), you are defining a -module of functionality.
+source tree, they live in the top level "include" directory), you are +defining a module of functionality.Ideally, modules should be completely independent of each other, and their -header files should only include the absolute minimum number of headers -possible. A module is not just a class, a function, or a namespace: it's a collection -of these that defines an interface. This interface may be several -functions, classes or data structures, but the important issue is how they work -together.
+header files should only #include the absolute minimum number of +headers possible. A module is not just a class, a function, or a +namespace: it's +a collection of these that defines an interface. This interface may be +several functions, classes, or data structures, but the important issue is how +they work together. -In general, a module should be implemented with one or more .cpp +
In general, a module should be implemented by one or more .cpp files. Each of these .cpp files should include the header that defines their interface first. This ensures that all of the dependences of the module header have been properly added to the module header itself, and are not @@ -503,29 +508,28 @@ translation unit.
#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 +
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 +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 -- you can -include them either directly -or indirectly (through another header file). To make sure that you don't -accidentally 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...
+must include all of the header files that you are using — you can +include them either directly or indirectly (through another header file). To +make sure that you don't accidentally 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.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.
+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.
-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 in a public +class itself. Just make them private (or protected) and all is well.
@@ -571,23 +575,23 @@ Value *DoSomething(Instruction *I) {
This code has several problems if the body of the 'if' is large. When you're -looking at the top of the function, it isn't immediately clear that this -only does interesting things with non-terminator instructions, and only -applies to things with the other predicates. Second, it is relatively difficult -to describe (in comments) why these predicates are important because the if -statement makes it difficult to lay out the comments. Third, when you're deep -within the body of the code, it is indented an extra level. Finally, when -reading the top of the function, it isn't clear what the result is if the -predicate isn't true, you have to read to the end of the function to know that -it returns null.
+This code has several problems if the body of the 'if' is large. +When you're looking at the top of the function, it isn't immediately clear that +this only does interesting things with non-terminator instructions, and +only applies to things with the other predicates. Second, it is relatively +difficult to describe (in comments) why these predicates are important because +the if statement makes it difficult to lay out the comments. Third, +when you're deep within the body of the code, it is indented an extra level. +Finally, when reading the top of the function, it isn't clear what the result is +if the predicate isn't true; you have to read to the end of the function to know +that it returns null.
It is much preferred to format the code like this:
Value *DoSomething(Instruction *I) {
- // Terminators never need 'something' done to them because, ...
+ // Terminators never need 'something' done to them because ...
if (isa<TerminatorInst>(I))
return 0;
@@ -622,14 +626,13 @@ loops. A silly example is something like this:
When you have very very small loops, this sort of structure is fine, but if +
When you have very, very small loops, this sort of structure is fine. But if it exceeds more than 10-15 lines, it becomes difficult for people to read and -understand at a glance. -The problem with this sort of code is that it gets very nested very quickly, -meaning that the reader of the code has to keep a lot of context in their brain -to remember what is going immediately on in the loop, because they don't know -if/when the if conditions will have elses etc. It is strongly preferred to -structure the loop like this:
+understand at a glance. The problem with this sort of code is that it gets very +nested very quickly. Meaning that the reader of the code has to keep a lot of +context in their brain to remember what is going immediately on in the loop, +because they don't know if/when the if conditions will have elses etc. +It is strongly preferred to structure the loop like this:
@@ -640,16 +643,17 @@ structure the loop like this:
Value *LHS = BO->getOperand(0);
Value *RHS = BO->getOperand(1);
if (LHS == RHS) continue;
+
...
}
This has all the benefits of using early exits from functions: it reduces +
This has all the benefits of using early exits for functions: it reduces nesting of the loop, it makes it easier to describe why the conditions are true, -and it makes it obvious to the reader that there is no else coming up that -they have to push context into their brain for. If a loop is large, this can -be a big understandability win.
+and it makes it obvious to the reader that there is no else coming up +that they have to push context into their brain for. If a loop is large, this +can be a big understandability win. @@ -661,10 +665,10 @@ be a big understandability win.For similar reasons above (reduction of indentation and easier reading), - please do not use else or 'else if' after something that interrupts - control flow like return, break, continue, goto, etc. For example, this is - "bad":
- +please do not use 'else' or 'else if' after something that +interrupts control flow — like return, break, +continue, goto, etc. For example, this is bad: +
case 'J': {
@@ -673,24 +677,24 @@ be a big understandability win.
if (Type.isNull()) {
Error = ASTContext::GE_Missing_sigjmp_buf;
return QualType();
- } else {
+ } else {
break;
- }
+ }
} else {
Type = Context.getjmp_bufType();
if (Type.isNull()) {
Error = ASTContext::GE_Missing_jmp_buf;
return QualType();
- } else {
+ } else {
break;
- }
+ }
}
}
}
It is better to write this something like:
+It is better to write it like this:
@@ -708,11 +712,11 @@ be a big understandability win.
return QualType();
}
}
- break;
+ break;
Or better yet (in this case), as:
+Or better yet (in this case) as:
@@ -727,12 +731,12 @@ be a big understandability win.
ASTContext::GE_Missing_jmp_buf;
return QualType();
}
- break;
+ break;
The idea is to reduce indentation and the amount of code you have to keep - track of when reading the code.
+track of when reading the code.It is very common to write small loops that just compute a boolean - value. There are a number of ways that people commonly write these, but an - example of this sort of thing is:
+It is very common to write small loops that just compute a boolean value. +There are a number of ways that people commonly write these, but an example of +this sort of thing is:
@@ -766,9 +770,7 @@ be a big understandability win. Instead of this sort of loop, we strongly prefer to use a predicate function (which may be static) that uses early exits to compute the predicate. We prefer -the code to be structured like this: - - +the code to be structured like this:@@ -814,47 +816,43 @@ locality.-Poorly-chosen names can mislead the reader and cause bugs. We cannot -stress enough how important it is to use descriptive names. -Pick names that match the semantics and role of the underlying -entities, within reason. Avoid abbreviations unless they are well -known. After picking a good name, make sure to use consistent capitalization -for the name, as inconsistency requires clients to either memorize the APIs or -to look it up to find the exact spelling. -
+ +Poorly-chosen names can mislead the reader and cause bugs. We cannot stress +enough how important it is to use descriptive names. Pick names that +match the semantics and role of the underlying entities, within reason. Avoid +abbreviations unless they are well known. After picking a good name, make sure +to use consistent capitalization for the name, as inconsistency requires clients +to either memorize the APIs or to look it up to find the exact spelling.
In general, names should be in camel case (e.g. TextFileReader -and isLValue()). Different kinds of declarations have different rules: -
+and isLValue()). Different kinds of declarations have different +rules:+
- + TextFileReader).
Type names (including classes, structs, enums, typedefs, etc) should be nouns and start with an upper-case letter (e.g. - TextFileReader).
-- + or isFoo()). -
Function names should be verb phrases (as they represent actions), and command-like function should be imperative. The name should be camel case, and start with a lower case letter (e.g. openFile() - or isFoo()).
-- - -
Enum declarations (e.g. "enum Foo {...}") are types, so they -should follow the naming conventions for types. A common use for enums is as a - discriminator for a union, or an indicator of a subclass. When an enum is - used for something like this, it should have a "Kind" suffix (e.g. - "ValueKind").
-Enumerators (e.g. enum { Foo, Bar }) and -public member variables should start with an upper-case letter, just -like types. Unless the enumerators are defined in their own small -namespace or inside a class, enumerators should have a prefix corresponding -to the enum declaration name. For example, enum ValueKind { ... }; -may contain enumerators like VK_Argument, VK_BasicBlock, -etc. Enumerators that are just convenience constants are exempt from the -requirement for a prefix. For instance:
+- +
Enum declarations (e.g. enum Foo {...}) are types, so + they should follow the naming conventions for types. A common use for enums + is as a discriminator for a union, or an indicator of a subclass. When an + enum is used for something like this, it should have a Kind suffix + (e.g. ValueKind).
- +
Enumerators (e.g. enum { Foo, Bar }) and public member + variables should start with an upper-case letter, just like types. + Unless the enumerators are defined in their own small namespace or inside a + class, enumerators should have a prefix corresponding to the enum + declaration name. For example, enum ValueKind { ... }; may contain + enumerators like VK_Argument, VK_BasicBlock, etc. + Enumerators that are just convenience constants are exempt from the + requirement for a prefix. For instance:
+-enum { @@ -863,16 +861,16 @@ enum { };As an exception, classes that mimic STL classes can have member names in +STL's style of lower-case words separated by underscores (e.g. begin(), +push_back(), and empty()).
-As an exception, classes that mimic STL classes can have member names -in STL's style of lower-case words separated by underscores -(e.g. begin(), push_back(), and empty()).
+Here are some examples of good and bad names:
-Here are some examples of bad and good names:
-class VehicleMaker { @@ -884,8 +882,8 @@ class VehicleMaker { }; Vehicle MakeVehicle(VehicleType Type) { - VehicleMaker M; // Might be OK if having a short life-span. - Tire tmp1 = M.makeTire(); // Bad -- 'tmp1' provides no information. + VehicleMaker M; // Might be OK if having a short life-span. + Tire tmp1 = M.makeTire(); // Bad -- 'tmp1' provides no information. Light headlight = M.makeLight("head"); // Good -- descriptive. ... } @@ -910,7 +908,7 @@ 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 +in the assertion statement, which is printed if the assertion is tripped. This helps the poor debugger make sense of why an assertion is being made and enforced, and hopefully what to do about it. Here is one complete example:
@@ -923,7 +921,7 @@ inline Value *getOperand(unsigned i) {Here are some examples:
+Here are more examples:
-@@ -939,9 +937,9 @@ assert(isa<PHINode>(Succ->front()) && "Only works on PHId BBs!"You get the idea...
+You get the idea.
-Please be aware when adding assert statements that not all compilers are aware of +
Please be aware that, when adding assert statements, not all compilers are aware of the semantics of the assert. In some places, asserts are used to indicate a piece of code that should not be reached. These are typically of the form:
@@ -965,33 +963,33 @@ return 0;Another issue is that values used only by assertions will produce an "unused - value" warning when assertions are disabled. For example, this code will warn: -
+value" warning when assertions are disabled. For example, this code will +warn:-- unsigned Size = V.size(); - assert(Size > 42 && "Vector smaller than it should be"); +unsigned Size = V.size(); +assert(Size > 42 && "Vector smaller than it should be"); - bool NewToSet = Myset.insert(Value); - assert(NewToSet && "The value shouldn't be in the set yet"); +bool NewToSet = Myset.insert(Value); +assert(NewToSet && "The value shouldn't be in the set yet");These are two interesting different cases: in the first case, the call to +
These are two interesting different cases. In the first case, the call to V.size() is only useful for the assert, and we don't want it executed when assertions are disabled. Code like this should move the call into the assert itself. In the second case, the side effects of the call must happen whether -the assert is enabled or not. In this case, the value should be cast to void -to disable the warning. To be specific, it is preferred to write the code -like this:
+the assert is enabled or not. In this case, the value should be cast to void to +disable the warning. To be specific, it is preferred to write the code like +this:@@ -1000,10 +998,11 @@ like this:- assert(V.size() > 42 && "Vector smaller than it should be"); +assert(V.size() > 42 && "Vector smaller than it should be"); - bool NewToSet = Myset.insert(Value); (void)NewToSet; - assert(NewToSet && "The value shouldn't be in the set yet"); +bool NewToSet = Myset.insert(Value); (void)NewToSet; +assert(NewToSet && "The value shouldn't be in the set yet");+In LLVM, we prefer to explicitly prefix all identifiers from the standard namespace with an "std::" prefix, rather than rely on "using namespace std;".
@@ -1015,7 +1014,7 @@ clearly a bad thing.In implementation files (e.g. .cpp files), the rule is more of a stylistic rule, but is still important. Basically, using explicit namespace prefixes makes the code clearer, because it is immediately obvious what facilities -are being used and where they are coming from, and more portable, because +are being used and where they are coming from. And more portable, because namespace clashes cannot occur between LLVM code and other namespaces. The portability rule is important because different standard library implementations expose different symbols (potentially ones they shouldn't), and future revisions @@ -1026,7 +1025,7 @@ such, we never use 'using namespace std;' in LLVM.
the std namespace) is for implementation files. For example, all of the code in the LLVM project implements code that lives in the 'llvm' namespace. As such, it is ok, and actually clearer, for the .cpp files to have a -'using namespace llvm' directive at their top, after the +'using namespace llvm;' directive at the top, after the #includes. This reduces indentation in the body of the file for source editors that indent based on braces, and keeps the conceptual context cleaner. The general form of this rule is that any .cpp file that implements @@ -1037,8 +1036,8 @@ use any others.- Provide a virtual method anchor for classes - in headers + Provide a Virtual Method Anchor for Classes + in Headers@@ -1054,15 +1053,16 @@ increasing link times.-Because C++ doesn't have a standard "foreach" loop (though it can be emulated -with macros and may be coming in C++'0x) we end up writing a lot of loops that -manually iterate from begin to end on a variety of containers or through other -data structures. One common mistake is to write a loop in this style:
+Because C++ doesn't have a standard "foreach" loop (though it can be +emulated with macros and may be coming in C++'0x) we end up writing a lot of +loops that manually iterate from begin to end on a variety of containers or +through other data structures. One common mistake is to write a loop in this +style:
@@ -1093,10 +1093,10 @@ behavior, please write the loop in the first form and add a comment indicating that you did it intentionally.Why do we prefer the second form (when correct)? Writing the loop in the -first form has two problems: First it may be less efficient than evaluating it -at the start of the loop. In this case, the cost is probably minor: a few extra -loads every time through the loop. However, if the base expression is more -complex, then the cost can rise quickly. I've seen loops where the end +first form has two problems. First it may be less efficient than evaluating it +at the start of the loop. In this case, the cost is probably minor — a +few extra loads every time through the loop. However, if the base expression is +more complex, then the cost can rise quickly. I've seen loops where the end expression was actually something like: "SomeMap[x]->end()" and map lookups really aren't cheap. By writing it in the second form consistently, you eliminate the issue entirely and don't even have to think about it.
@@ -1115,7 +1115,7 @@ prefer it.@@ -1124,12 +1124,13 @@ prefer it. hereby forbidden. The primary reason for doing this is to support clients using LLVM libraries as part of larger systems. In particular, we statically link LLVM into some dynamic libraries. Even if LLVM isn't used, -the static c'tors are run whenever an application start up that uses the dynamic -library. There are two problems with this: +the static constructors are run whenever an application starts up that uses the +dynamic library. There are two problems with this:-
- The time to run the static c'tors impacts startup time of - applications—a critical time for GUI apps.
+- The time to run the static c'tors impacts startup time of applications + — a critical time for GUI apps.
+- The static c'tors cause the app to pull many extra pages of memory off the disk: both the code for the static c'tors in each .o file and the small amount of data that gets touched. In addition, touched/dirty pages @@ -1137,10 +1138,10 @@ library. There are two problems with this:
Note that using the other stream headers (<sstream> for -example) is not problematic in this regard (just <iostream>). -However, raw_ostream provides various APIs that are better performing for almost -every use than std::ostream style APIs. -Therefore new code should always +example) is not problematic in this regard — +just <iostream>. However, raw_ostream provides various +APIs that are better performing for almost every use than std::ostream +style APIs. Therefore new code should always use raw_ostream for writing, or the llvm::MemoryBuffer API for reading files.
@@ -1155,9 +1156,9 @@ the llvm::MemoryBuffer API for reading files.LLVM includes a lightweight, simple, and efficient stream implementation -in llvm/Support/raw_ostream.h which provides all of the common features -of std::ostream. All new code should use raw_ostream instead -of ostream.
+in llvm/Support/raw_ostream.h, which provides all of the common +features of std::ostream. All new code should use raw_ostream +instead of ostream.Unlike std::ostream, raw_ostream is not a template and can be forward declared as class raw_ostream. Public headers should @@ -1174,9 +1175,9 @@ declarations and constant references to raw_ostream instances.
-The std::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 std::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:
@@ -1213,48 +1214,48 @@ macros. For example, this is good:-- if (x) ... - for (i = 0; i != 100; ++i) ... - while (llvm_rocks) ... +if (x) ... +for (i = 0; i != 100; ++i) ... +while (llvm_rocks) ... - somefunc(42); - assert(3 != 4 && "laws of math are failing me"); +somefunc(42); +assert(3 != 4 && "laws of math are failing me"); - a = foo(42, 92) + bar(x); -+a = foo(42, 92) + bar(x); +... and this is bad:
+and this is bad:
- if(x) ... - for(i = 0; i != 100; ++i) ... - while(llvm_rocks) ... +if(x) ... +for(i = 0; i != 100; ++i) ... +while(llvm_rocks) ... - somefunc (42); - assert (3 != 4 && "laws of math are failing me"); +somefunc (42); +assert (3 != 4 && "laws of math are failing me"); - a = foo (42, 92) + bar (x); +a = foo (42, 92) + bar (x);The reason for doing this is not completely arbitrary. This style makes - control flow operators stand out more, and makes expressions flow better. The - function call operator binds very tightly as a postfix operator. Putting - a space after a function name (as in the last example) makes it appear that - the code might bind the arguments of the left-hand-side of a binary operator - with the argument list of a function and the name of the right side. More - specifically, it is easy to misread the "a" example as:
+control flow operators stand out more, and makes expressions flow better. The +function call operator binds very tightly as a postfix operator. Putting a +space after a function name (as in the last example) makes it appear that the +code might bind the arguments of the left-hand-side of a binary operator with +the argument list of a function and the name of the right side. More +specifically, it is easy to misread the "a" example as:-- a = foo ((42, 92) + bar) (x); +a = foo ((42, 92) + bar) (x);... when skimming through the code. By avoiding a space in a function, we -avoid this misinterpretation.
+when skimming through the code. By avoiding a space in a function, we avoid +this misinterpretation.