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Diffstat (limited to 'docs/LangRef.rst')
| -rw-r--r-- | docs/LangRef.rst | 17 |
1 files changed, 13 insertions, 4 deletions
diff --git a/docs/LangRef.rst b/docs/LangRef.rst index 13706e167f..1e65f0b823 100644 --- a/docs/LangRef.rst +++ b/docs/LangRef.rst @@ -879,17 +879,22 @@ example: passes make choices that keep the code size of this function low, and otherwise do optimizations specifically to reduce code size. ``readnone`` - This attribute indicates that the function computes its result (or - decides to unwind an exception) based strictly on its arguments, + On a function, this attribute indicates that the function computes its + result (or decides to unwind an exception) based strictly on its arguments, without dereferencing any pointer arguments or otherwise accessing any mutable state (e.g. memory, control registers, etc) visible to caller functions. It does not write through any pointer arguments (including ``byval`` arguments) and never changes any state visible to callers. This means that it cannot unwind exceptions by calling the ``C++`` exception throwing methods. + + On an argument, this attribute indicates that the function does not + dereference that pointer argument, even though it may read or write the + memory that the pointer points to through if accessed through other + pointers. ``readonly`` - This attribute indicates that the function does not write through - any pointer arguments (including ``byval`` arguments) or otherwise + On a function, this attribute indicates that the function does not write + through any pointer arguments (including ``byval`` arguments) or otherwise modify any state (e.g. memory, control registers, etc) visible to caller functions. It may dereference pointer arguments and read state that may be set in the caller. A readonly function always @@ -897,6 +902,10 @@ example: called with the same set of arguments and global state. It cannot unwind an exception by calling the ``C++`` exception throwing methods. + + On an argument, this attribute indicates that the function does not write + through this pointer argument, even though it may write to the memory that + the pointer points to. ``returns_twice`` This attribute indicates that this function can return twice. The C ``setjmp`` is an example of such a function. The compiler disables |