rnk added inline comments.
================
Comment at: clang/lib/Sema/SemaDecl.cpp:14254
int SectionFlags = ASTContext::PSF_Read;
- if (var->getType().isConstQualified()) {
- if (HasConstInit)
----------------
rsmith wrote:
> efriedma wrote:
> > rnk wrote:
> > > I think this is not compatible with MSVC. MSVC uses simple logic, it
> > > doesn't look for mutable: https://gcc.godbolt.org/z/sj6d4saxx
> > >
> > > The const mutable struct appears in the myrdata section in that example.
> > >
> > > I think the solution is to separate the flag logic from the pragma stack
> > > selection logic, which has to remain MSVC-compatible.
> > MSVC apparently looks at whether the variable is marked "const", and
> > nothing else; it doesn't look at mutable, it doesn't look at whether the
> > variable has a constant initializer. So the current code isn't right
> > either; if we're trying to implement MSVC-compatible logic, we shouldn't
> > check HasConstInit.
> >
> > That said, I'm not sure how precisely/in what modes we want to precisely
> > emulate MSVC. Probably anything we do here will be confusing.
> We should at least issue a warning if the sensible logic and the
> MSVC-compatible calculation differ. @rnk, do you know how important it is to
> follow the MSVC semantics in this regard?
I think it depends on whether you think that users are primarily using these
pragmas to override the default rdata/bss/data sections without any care about
precisely what goes where, or if they are using them to do something finer
grained.
If I had to guess, I'd say it's more likely the former, given that
`__declspec(allocate)` and `#pragma(section)` exist to handle cases where users
are putting specific globals into specific sections.
Which, if we follow Richard's suggestion, would mean warning when we put a
global marked `const` into a writable section when `ConstSegStack` is
non-empty. That seems reasonable. `-Wmicrosoft-const-seg` for the new warning
group?
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D156726/new/
https://reviews.llvm.org/D156726
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