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[LangRef] add to description of alloca instruction 

As mentioned in D58359, we can explicitly state that the
memory allocated is uninitialized and reading that memory
produces undef.

llvm-svn: 354394
This commit is contained in:
Sanjay Patel 2019-02-19 22:35:12 +00:00
parent c1e0184317
commit b6bc11d406
1 changed files with 10 additions and 9 deletions
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19
llvm/docs/LangRef.rst
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@ -8364,15 +8364,16 @@ boundary compatible with the type.
Semantics:
""""""""""
Memory is allocated; a pointer is returned. The operation is undefined
if there is insufficient stack space for the allocation. '``alloca``'d
memory is automatically released when the function returns. The
'``alloca``' instruction is commonly used to represent automatic
variables that must have an address available. When the function returns
(either with the ``ret`` or ``resume`` instructions), the memory is
reclaimed. Allocating zero bytes is legal, but the returned pointer may not
be unique. The order in which memory is allocated (ie., which way the stack
grows) is not specified.
Memory is allocated; a pointer is returned. The allocated memory is
uninitialized, and loading from uninitialized memory produces an undefined
value. The operation itself is undefined if there is insufficient stack
space for the allocation.'``alloca``'d memory is automatically released
when the function returns. The '``alloca``' instruction is commonly used
to represent automatic variables that must have an address available. When
the function returns (either with the ``ret`` or ``resume`` instructions),
the memory is reclaimed. Allocating zero bytes is legal, but the returned
pointer may not be unique. The order in which memory is allocated (ie.,
which way the stack grows) is not specified.
Example:
""""""""