-.. _coding_standards:
-
=====================
LLVM Coding Standards
=====================
#. Main Module Header
#. Local/Private Headers
-#. ``llvm/*``
-#. ``llvm/Analysis/*``
-#. ``llvm/Assembly/*``
-#. ``llvm/Bitcode/*``
-#. ``llvm/CodeGen/*``
-#. ...
-#. ``llvm/Support/*``
-#. ``llvm/Config/*``
+#. ``llvm/...``
#. System ``#include``\s
-and each category should be sorted by name.
+and each category should be sorted lexicographically by the full path.
The `Main Module Header`_ file applies to ``.cpp`` files which implement an
interface defined by a ``.h`` file. This ``#include`` should always be included
That said, LLVM does make extensive use of a hand-rolled form of RTTI that use
templates like `isa<>, cast<>, and dyn_cast<> <ProgrammersManual.html#isa>`_.
-This form of RTTI is opt-in and can be added to any class. It is also
+This form of RTTI is opt-in and can be
+:doc:`added to any class <HowToSetUpLLVMStyleRTTI>`. It is also
substantially more efficient than ``dynamic_cast<>``.
.. _static constructor:
.. code-block:: c++
bool FoundFoo = false;
- for (unsigned i = 0, e = BarList.size(); i != e; ++i)
- if (BarList[i]->isFoo()) {
+ for (unsigned I = 0, E = BarList.size(); I != E; ++I)
+ if (BarList[I]->isFoo()) {
FoundFoo = true;
break;
}
/// \returns true if the specified list has an element that is a foo.
static bool containsFoo(const std::vector<Bar*> &List) {
- for (unsigned i = 0, e = List.size(); i != e; ++i)
- if (List[i]->isFoo())
+ for (unsigned I = 0, E = List.size(); I != E; ++I)
+ if (List[I]->isFoo())
return true;
return false;
}
Vehicle MakeVehicle(VehicleType Type) {
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.
+ Tire Tmp1 = M.makeTire(); // Bad -- 'Tmp1' provides no information.
+ Light Headlight = M.makeLight("head"); // Good -- descriptive.
...
}
.. code-block:: c++
- inline Value *getOperand(unsigned i) {
- assert(i < Operands.size() && "getOperand() out of range!");
- return Operands[i];
+ inline Value *getOperand(unsigned I) {
+ assert(I < Operands.size() && "getOperand() out of range!");
+ return Operands[I];
}
Here are more examples:
You get the idea.
-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:
+In the past, asserts were used to indicate a piece of code that should not be
+reached. These were typically of the form:
.. code-block:: c++
- assert(0 && "Some helpful error message");
+ assert(0 && "Invalid radix for integer literal");
+
+This has a few issues, the main one being that some compilers might not
+understand the assertion, or warn about a missing return in builds where
+assertions are compiled out.
-When used in a function that returns a value, they should be followed with a
-return statement and a comment indicating that this line is never reached. This
-will prevent a compiler which is unable to deduce that the assert statement
-never returns from generating a warning.
+Today, we have something much better: ``llvm_unreachable``:
.. code-block:: c++
- assert(0 && "Some helpful error message");
- return 0;
+ llvm_unreachable("Invalid radix for integer literal");
+
+When assertions are enabled, this will print the message if it's ever reached
+and then exit the program. When assertions are disabled (i.e. in release
+builds), ``llvm_unreachable`` becomes a hint to compilers to skip generating
+code for this branch. If the compiler does not support this, it will fall back
+to the "abort" implementation.
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:
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
+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.
Most of the time, you probably have no reason to flush the output stream, so
it's better to use a literal ``'\n'``.
+Don't use ``inline`` when defining a function in a class definition
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+A member function defined in a class definition is implicitly inline, so don't
+put the ``inline`` keyword in this case.
+
+Don't:
+
+.. code-block:: c++
+
+ class Foo {
+ public:
+ inline void bar() {
+ // ...
+ }
+ };
+
+Do:
+
+.. code-block:: c++
+
+ class Foo {
+ public:
+ void bar() {
+ // ...
+ }
+ };
+
Microscopic Details
-------------------
.. code-block:: c++
- if (x) ...
- for (i = 0; i != 100; ++i) ...
- while (llvm_rocks) ...
+ if (X) ...
+ for (I = 0; I != 100; ++I) ...
+ while (LLVMRocks) ...
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:
.. code-block:: c++
- if(x) ...
- for(i = 0; i != 100; ++i) ...
- while(llvm_rocks) ...
+ if(X) ...
+ for(I = 0; I != 100; ++I) ...
+ while(LLVMRocks) ...
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
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:
+misread the "``A``" example as:
.. code-block:: c++
- 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.
See Also
========
-A lot of these comments and recommendations have been culled for other sources.
+A lot of these comments and recommendations have been culled from other sources.
Two particularly important books for our work are:
#. `Effective C++