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Extend 'readonly' and 'readnone' to work on function arguments as well as

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functions. Make the function attributes pass add it to known library functions
and when it can deduce it.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@185735 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Nick Lewycky
2013-07-06 00:29:58 +00:00
parent 202eb7b18e
commit dc89737bcd
22 changed files with 547 additions and 86 deletions
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17
docs/LangRef.rst
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@@ -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