rsmith added a comment.
We've hit a fairly subtle miscompile caused by this patch.
glibc's setjmp.h looks like this (irrelevant parts removed):
struct __jmp_buf_tag { /*...*/ };
extern int __sigsetjmp(struct __jmp_buf_tag __env[1], int);
typedef struct __jmp_buf_tag sigjmp_buf[1];
#define sigsetjmp __sigsetjmp
This worked fine with the old approach. But with the new approach, we decide
the declaration of `__sigsetjmp` is not a builtin, because at its point of
declaration, we can't compute the "proper" type because `sigjmp_buf` has not
been declared yet. As a result, we don't add a `BuiltinAttr` to `__sigsetjmp`,
but much more critically, we don't add a `ReturnsTwiceAttr`, which results in
miscompiles in calls to this function. (I think `sigsetjmp` is the only
affected function with glibc. `jmp_buf` is declared prior to `__setjmp` and
friends.)
I suppose we don't actually care what the parameter types for `__sigsetjmp`
are, and it would be fine (and much safer) to treat any function with that name
as a builtin, like we used to. Perhaps we should have a way of marking builtins
as "the given type is what we expect / what we will implicitly declare, but
it's OK if it doesn't actually match"?
Repository:
rG LLVM Github Monorepo
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https://reviews.llvm.org/D77491/new/
https://reviews.llvm.org/D77491
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