yiranwang added a comment.
A test case is as following. It has to be build by GCC 4.9 -O3 (maybe or
later), with latest libc++, and for AARCH64+ANDROID target.
AARCH64 requires 128 bit alignment for aligned_storage and 64 bit pointers,
while gcc 4.9 alias analysis will do field-sensitive points-to analysis. But
this could happen for other ISA+ABI.
The fundamental issue is that for this combination, std::function has member
__buf_ declared as
aligned_storage<3*sizoef(void*)>::type __buf_;
Basically, it is
aligned_storage<24>::type;
This will generate aligned_storage of, _Len==24 and _Align==16;
While std::function will use the __buf_ to sizeof(__buf_) bytes (at line 1593
and 1628 of <functional>), which is 32. Basically, the pointer to "tbool' will
be stored at "&__buf_+24".
This is not a well defined memory area, and GCC alias analysis is going to
ignore the "ESCAPE" of address of "tbool". Basically, the function
"test_simple" would always return "false".
#include <functional>
extern void external_test(std::function<bool()>fn);
extern bool test_simple(){
bool tbool = false;
int a, b;
external_test([&a, &b, &tbool](){
tbool = true;
return true;
});
return tbool;
}
http://reviews.llvm.org/D12247
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