hoy added a subscriber: bruno.
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:
> > > > > > > > > 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.
> Are you undertaking that investigation? It'd be good to address this
> divergence if possible.
>
> (@aprantl or @rsmith maybe you know something about this ObjC thing? )
Haven't figured out anything useful yet. As far as I can tell, the debug info
generation code is shared between C++ and ObjC. Using
`getAs<FunctionProtoType>` works for C++ but not for ObjectC where it crashes
when computing a mangled name for something like
```
void test() {
__block A a;
^{ (void)a; };
}
```
Below are the failing tests which are all like that:
Clang :: CodeGenCXX/cp-blocks-linetables.cpp
Clang :: CodeGenCXX/debug-info-block-invocation-linkage-name.cpp
Clang :: CodeGenCXX/debug-info-blocks.cpp
Clang :: CodeGenObjCXX/nested-ehlocation.mm
Clang :: CodeGenObjCXX/property-objects.mm
Clang :: CodeGenObjCXX/synthesized-property-cleanup.mm
cc @bruno
Repository:
rG LLVM Github Monorepo
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https://reviews.llvm.org/D98799/new/
https://reviews.llvm.org/D98799
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