diff options
Diffstat (limited to 'llvm/docs/LangRef.rst')
| -rw-r--r-- | llvm/docs/LangRef.rst | 30 |
1 files changed, 24 insertions, 6 deletions
diff --git a/llvm/docs/LangRef.rst b/llvm/docs/LangRef.rst index b99a96f..eb2ef6b 100644 --- a/llvm/docs/LangRef.rst +++ b/llvm/docs/LangRef.rst @@ -3356,6 +3356,19 @@ behavior is undefined: - the size of all allocated objects must be non-negative and not exceed the largest signed integer that fits into the index type. +Allocated objects that are created with operations recognized by LLVM (such as +:ref:`alloca <i_alloca>`, heap allocation functions marked as such, and global +variables) may *not* change their size. (``realloc``-style operations do not +change the size of an existing allocated object; instead, they create a new +allocated object. Even if the object is at the same location as the old one, old +pointers cannot be used to access this new object.) However, allocated objects +can also be created by means not recognized by LLVM, e.g. by directly calling +``mmap``. Those allocated objects are allowed to grow to the right (i.e., +keeping the same base address, but increasing their size) while maintaining the +validity of existing pointers, as long as they always satisfy the properties +described above. Currently, allocated objects are not permitted to grow to the +left or to shrink, nor can they have holes. + .. _objectlifetime: Object Lifetime @@ -11928,6 +11941,9 @@ if the ``getelementptr`` has any non-zero indices, the following rules apply: :ref:`based <pointeraliasing>` on. This means that it points into that allocated object, or to its end. Note that the object does not have to be live anymore; being in-bounds of a deallocated object is sufficient. + If the allocated object can grow, then the relevant size for being *in + bounds* is the maximal size the object could have while satisfying the + allocated object rules, not its current size. * During the successive addition of offsets to the address, the resulting pointer must remain *in bounds* of the allocated object at each step. @@ -26637,9 +26653,10 @@ object's lifetime. Arguments: """""""""" -The first argument is a constant integer representing the size of the -object, or -1 if it is variable sized. The second argument is a pointer -to an ``alloca`` instruction. +The first argument is a constant integer, which is ignored and will be removed +in the future. + +The second argument is a pointer to an ``alloca`` instruction. Semantics: """""""""" @@ -26677,9 +26694,10 @@ The '``llvm.lifetime.end``' intrinsic specifies the end of a Arguments: """""""""" -The first argument is a constant integer representing the size of the -object, or -1 if it is variable sized. The second argument is a pointer -to an ``alloca`` instruction. +The first argument is a constant integer, which is ignored and will be removed +in the future. + +The second argument is a pointer to an ``alloca`` instruction. Semantics: """""""""" |