Change mechanism used to ensure #pragma rs reduce functions are not deleted.
Requires corresponding change in frameworks/compile/libbcc.
The functions referenced by "#pragma rs reduce" are static functions.
If the only references to such a function are from these pragmas, then
the function looks unreferenced, and hence without additional work
will be deleted by clang.
The old solution to this problem is to add all such functions to
the LLVM intrinsic variable @llvm.used. Unfortunately, this
doesn't just prevent clang from deleting these functions -- it
also prevents llvm from deleting these functions. This is
undesirable in the case of the combiner function (which is not
currently needed by the CPU reference driver) or the accumulator
function (because the CPU reference driver needs an "expanded"
form of the accumulator function, not the original accumulator
function).
The new solution is that for each such function "f" we generate a
dummy variable initialized with a pointer to that function:
void *.rs.reduce_fn.f = (void*)&f;
This prevents clang from deleting "f", but does not automatically
prevent llvm from deleting "f" (e.g., the backend could use some
other mechanism to retain "f" if necessary, while
deleting ".rs.reduce_fn.f").
Bug: 23535724
Change-Id: Ic5e6fdcc305f2699a3b0ddb09f07a6a36c7d6c07
10 files changed
