kosarev added a comment.
Now that https://reviews.llvm.org/D38796 is comitted and added the
tbaa-cast.cpp test case to the mainline, we fail on it with this patch applied.
The reason is that we have no special TBAA type node for may-alias accesses, so
everything that ever been a potential access to a character type turns into a
may-alias access and propagates as such.
The test case reads:
struct V {
unsigned n;
};
struct S {
char bytes[4];
};
void foo(S *p) {
((V*)p->bytes)->n = 5;
}
Here, p->bytes decays to a pointer to char, meaning the pointee object is
considered may-alias and so it is after the explicit cast.
This arises an interesting question: should we introduce a special
representation for may-alias accesses to distinct them from character-typed
accesses? Or, maybe explicit casts should not derive their may-alias'ness from
their source operands? Or, maybe we want to consider all explicit casts of the
form ##(T*)E## where ##T*## and ##typeof(E)## point to different types as
pointers to may-alias objects?
Repository:
rL LLVM
https://reviews.llvm.org/D39008
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