efriedma requested changes to this revision.
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We really should be checking this much earlier.
IsGlobalLValue() in ExprConstant.cpp is the canonical place to answer the
question "is the address of the given expression constant". Getting this right
in semantic analysis means you don't have to chase down all the various places
which generate global initializers. In addition to global variables, static
local variables and compound literals can have static storage duration in C.
And sometimes you can even run into trouble with globals which don't exist in
the source code. One interesting example:
int a;
int g(const int**);
int f(void) {
const int *x[] = {&a,&a,&a,&a,&a,&a,&a,&a};
return g(x);
}
This is valid code whether or not we're in rwpi mode, but clang currently
generates IR which won't link in rwpi mode. If semantic analysis concludes
that `&a` isn't a constant, the correct code generation falls out naturally;
otherwise, you have yet another place to add an explicit check in IR
generation. And I won't even try to go into all the additional corner cases
you can run into with C++ code.
As a bonus, you can generate nicer error messages in Sema.
https://reviews.llvm.org/D28526
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