hoy 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;
+}
+
+
----------------
dblaikie wrote:
> 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.
I took another look. I think the divergence comes from
`getAs<FunctionProtoType>` vs `hasPrototype`. The debug data generation uses
`hasPrototype` while `getAs<FunctionProtoType>` is used as overloadable
attribute processing as long as unique linkage name processing before this
change. More specifically, the following function definition is represented by
`FunctionProtoType` while it does not `hasPrototype`.
```
static int go(a) int a; {
return 3 + a;
}
```
I was trying to have `CGDebugInfo` to check `FunctionProtoType` instead of
`hasPrototype`. While it works for the code pattern in discussion, it also
breaks other tests including objectC tests. More investigation is needed to
understand what each term really means.
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D98799/new/
https://reviews.llvm.org/D98799
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