dblaikie added inline comments.
================
Comment at: clang/test/CodeGen/unique-internal-linkage-names-dwarf.c:34-39
+static int go(a) int a;
+{
+ return glob + a;
+}
+
+
----------------
hoy wrote:
> dblaikie wrote:
> > hoy wrote:
> > > dblaikie wrote:
> > > > hoy wrote:
> > > > > dblaikie wrote:
> > > > > > hoy wrote:
> > > > > > > dblaikie wrote:
> > > > > > > > Does this need to be down here? Or would the code be a well
> > > > > > > > exercised if it was up next to the go declaration above?
> > > > > > > Yes, it needs to be here. Otherwise it will just like the
> > > > > > > function `bar` above that doesn't get a uniquefied name. I think
> > > > > > > moving the definition up to right after the declaration hides the
> > > > > > > declaration.
> > > > > > Not sure I follow - do you mean that if the go declaration and go
> > > > > > definition were next to each other, this test would (mechanically
> > > > > > speaking) not validate what the patch? Or that it would be less
> > > > > > legible, but still mechanically correct?
> > > > > >
> > > > > > I think it would be (assuming it's still mechanically correct) more
> > > > > > legible to put the declaration next to the definition - the comment
> > > > > > describes why the declaration is significant/why the definition is
> > > > > > weird, and seeing all that together would be clearer to me than
> > > > > > spreading it out/having to look further away to see what's going on.
> > > > > When the `go` declaration and `go` definition were next to each
> > > > > other, the go function won't get a uniqufied name at all. The
> > > > > declaration will be overwritten by the definition. Only when the
> > > > > declaration is seen by others, such the callsite in `baz`, the
> > > > > declaration makes a difference by having the callsite use a uniqufied
> > > > > name.
> > > > >
> > > > >
> > > > Ah! Interesting, good to know.
> > > >
> > > > Is that worth supporting, I wonder? I guess it falls out for
> > > > free/without significant additional complexity. I worry about the
> > > > subtlety of the additional declaration changing the behavior here...
> > > > might be a bit surprising/subtle. But maybe no nice way to avoid it
> > > > either.
> > > It would be ideal if user never writes code like that. Unfortunately it
> > > exists with legacy code (such as mysql). I think it's worth supporting it
> > > from AutoFDO point of view to avoid a silent mismatch between debug
> > > linkage name and real linkage name.
> > Oh, I agree that we shouldn't mismatch debug info and the actual symbol
> > name - what I meant was whether code like this should get mangled or not
> > when using unique-internal-linkage names.
> >
> > I'm now more curious about this:
> >
> > > When the `go` declaration and `go` definition were next to each other,
> > > the go function won't get a uniqufied name at all.
> >
> > This doesn't seem to happen with the `__attribute__((overloadable))`
> > attribute, for instance - so any idea what's different about uniquification
> > that's working differently than overloadable?
> >
> > ```
> > $ cat test.c
> > __attribute__((overloadable)) static int go(a) int a; {
> > return 3 + a;
> > }
> > void baz() {
> > go(2);
> > }
> > $ clang-tot test.c -emit-llvm -S -o - | grep go
> > %call = call i32 @_ZL2goi(i32 2)
> > define internal i32 @_ZL2goi(i32 %a) #0 {
> > ```
> Good question. I'm not sure what's exactly going on but it looks like with
> the overloadable attribute, the old-style definition is treated as having
> prototype. But if you do this:
>
> ```
> __attribute__((overloadable))
> void baz() {}
> ```
> then there's the error:
>
> ```
> error: 'overloadable' function 'baz' must have a prototype
> void baz() {
> ```
>
> `void baz() {` does not come with a prototype. That's for sure. Sounds like
> `int go(a) int a {;` can have a prototype when it is loadable. I'm wondering
> why it's not always treated as having prototype, since the parameter type is
> there.
>
>
>
Yeah, that seems like that divergence be worth understanding (& if possible
fixing/avoiding/merging). Ensuring these features don't have subtle divergence
I think will be valuable to having a model that's easy to
explain/understand/modify/etc.
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D98799/new/
https://reviews.llvm.org/D98799
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