aaron.ballman 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:
> aaron.ballman wrote:
> > hoy wrote:
> > > aaron.ballman wrote:
> > > > dblaikie wrote:
> > > > > hoy wrote:
> > > > > > dblaikie wrote:
> > > > > > > hoy wrote:
> > > > > > > > dblaikie wrote:
> > > > > > > > > aaron.ballman wrote:
> > > > > > > > > > dblaikie wrote:
> > > > > > > > > > > aaron.ballman wrote:
> > > > > > > > > > > > dblaikie wrote:
> > > > > > > > > > > > > hoy wrote:
> > > > > > > > > > > > > > dblaikie wrote:
> > > > > > > > > > > > > > > dblaikie wrote:
> > > > > > > > > > > > > > > > hoy wrote:
> > > > > > > > > > > > > > > > > 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
> > > > > > > > > > > > > > > > Ping on this - anyone got a chance to take a
> > > > > > > > > > > > > > > > look? It'd be great to avoid this subtle
> > > > > > > > > > > > > > > > inconsistency.
> > > > > > > > > > > > > > > Ping again
> > > > > > > > > > > > > > I tried a different route instead of using
> > > > > > > > > > > > > > `getAs<FunctionProtoType>` in debug info generation
> > > > > > > > > > > > > > which beaks the blocks function and objectC cases.
> > > > > > > > > > > > > > Since the problem here is that the old-C function
> > > > > > > > > > > > > > (`bar` in the test case) is not considered
> > > > > > > > > > > > > > `hasPrototype`, I tried to unify `isKNRPrototype`
> > > > > > > > > > > > > > and `hasPrototype` so that old-C functions are
> > > > > > > > > > > > > > considered `hasPrototype`. It works for the name
> > > > > > > > > > > > > > mangler but it breaks other places where
> > > > > > > > > > > > > > `isKNRPrototype` should be excluded from
> > > > > > > > > > > > > > `hasPrototype`.
> > > > > > > > > > > > > Hrm - I'd really like to get to the bottom of this,
> > > > > > > > > > > > > but not sure who to pull in.
> > > > > > > > > > > > >
> > > > > > > > > > > > > @aaron.ballman - do you know who might have some idea
> > > > > > > > > > > > > of how these different old KNR C declarations work,
> > > > > > > > > > > > > and how this code might be made more robust?
> > > > > > > > > > > > Ugh, prototypes. They're not particularly well
> > > > > > > > > > > > specified in the C standard IMHO. In C, a function with
> > > > > > > > > > > > a prototype is one that declares the types of its
> > > > > > > > > > > > parameters (C17 6.2.1p2) which is further clarified to
> > > > > > > > > > > > be a function type with a parameter type list
> > > > > > > > > > > > explicitly (C17 6.2.7p3, 6.9.1p7). However, the very
> > > > > > > > > > > > end of 6.9.1p7 goes on to say that once you see the
> > > > > > > > > > > > definition of the function, you know about its
> > > > > > > > > > > > parameter type information, but it doesn't clarify
> > > > > > > > > > > > whether this means the function now has a prototype or
> > > > > > > > > > > > not.
> > > > > > > > > > > >
> > > > > > > > > > > > The result of this is that:
> > > > > > > > > > > > ```
> > > > > > > > > > > > void f();
> > > > > > > > > > > > void call_it_once(void) { f(1.2f); }
> > > > > > > > > > > >
> > > > > > > > > > > > void f(a) float a; {}
> > > > > > > > > > > > void call_if_twice(void) { f(1.2f); }
> > > > > > > > > > > > ```
> > > > > > > > > > > > in `call_it_once`, the argument is promoted to a
> > > > > > > > > > > > double, while in `call_it_twice`, the argument is not.
> > > > > > > > > > > > I suspect we're hitting another variation of this
> > > > > > > > > > > > confusing behavior here.
> > > > > > > > > > > >
> > > > > > > > > > > @aaron.ballman Thanks for taking a look.
> > > > > > > > > > >
> > > > > > > > > > > Do you know if/how this code could be phrased so that
> > > > > > > > > > > this code:
> > > > > > > > > > > ```
> > > > > > > > > > > static int go(int);
> > > > > > > > > > >
> > > > > > > > > > > void baz() {
> > > > > > > > > > > foo();
> > > > > > > > > > > bar(1);
> > > > > > > > > > > go(2);
> > > > > > > > > > > }
> > > > > > > > > > >
> > > > > > > > > > > static int go(a) int a;
> > > > > > > > > > > {
> > > > > > > > > > > return glob + a;
> > > > > > > > > > > }
> > > > > > > > > > > ```
> > > > > > > > > > >
> > > > > > > > > > > Could test some property of `go` at the function call
> > > > > > > > > > > site that would be consistent whether the definition of
> > > > > > > > > > > `go` came before or after the call site? It seems
> > > > > > > > > > > currently this code behaves differently depending on that
> > > > > > > > > > > order and I think that's a bit of a sharp corner it'd be
> > > > > > > > > > > good not to have, if there's a tidier/more consistent way
> > > > > > > > > > > to phrase the code.
> > > > > > > > > > To be honest, I wasn't aware this code was even valid
> > > > > > > > > > (where you mix and match between identifier lists and
> > > > > > > > > > parameter type lists), so that's neat.
> > > > > > > > > >
> > > > > > > > > > I might be confused, but in my tests, the behavior of
> > > > > > > > > > `collectFunctionDeclProps()` is the same regardless of
> > > > > > > > > > order, but the calls to `isUniqueInternalLinkageDecl()` are
> > > > > > > > > > different. Given an invocation of: `-cc1 -triple
> > > > > > > > > > x86_64-unknown-linux -debug-info-kind=limited
> > > > > > > > > > -dwarf-version=4 -funique-internal-linkage-names -emit-llvm
> > > > > > > > > > -o - test.c` with test.c as:
> > > > > > > > > > ```
> > > > > > > > > > static int go(int);
> > > > > > > > > >
> > > > > > > > > > static int go(a) int a;
> > > > > > > > > > {
> > > > > > > > > > return 1 + a;
> > > > > > > > > > }
> > > > > > > > > >
> > > > > > > > > > void baz() {
> > > > > > > > > > go(2);
> > > > > > > > > > }
> > > > > > > > > > ```
> > > > > > > > > > I see `isUniqueInternalLinkageDecl()` gets called:
> > > > > > > > > > * once for `go` with no prototype
> > > > > > > > > > * once for `baz` with no prototype
> > > > > > > > > >
> > > > > > > > > > and `collectFunctionDeclProps()` gets called:
> > > > > > > > > > * once for `baz` with no prototype
> > > > > > > > > > * once for `go` with a prototype
> > > > > > > > > >
> > > > > > > > > > The end result is that I see `!13 = distinct
> > > > > > > > > > !DISubprogram(name: "go", scope: !8, file: !8, line: 3,
> > > > > > > > > > type: !14, scopeLine: 4, flags: DIFlagPrototyped, spFlags:
> > > > > > > > > > DISPFlagLocalToUnit | DISPFlagDefinition, unit: !0,
> > > > > > > > > > retainedNodes: !2)` in the output.
> > > > > > > > > >
> > > > > > > > > > However, with test.c as:
> > > > > > > > > > ```
> > > > > > > > > > static int go(int);
> > > > > > > > > >
> > > > > > > > > > void baz() {
> > > > > > > > > > go(2);
> > > > > > > > > > }
> > > > > > > > > >
> > > > > > > > > > static int go(a) int a;
> > > > > > > > > > {
> > > > > > > > > > return 1 + a;
> > > > > > > > > > }
> > > > > > > > > > ```
> > > > > > > > > > I see `isUniqueInternalLinkageDecl()` gets called:
> > > > > > > > > > * once for `baz` with no prototype
> > > > > > > > > > * once for `go` with a prototype
> > > > > > > > > > * another one for `go` with a prototype
> > > > > > > > > >
> > > > > > > > > > and `collectFunctionDeclProps()` gets called:
> > > > > > > > > > * once for `baz` with no prototype
> > > > > > > > > > * once for `go` with a prototype
> > > > > > > > > >
> > > > > > > > > > The end result is that I see `!13 = distinct
> > > > > > > > > > !DISubprogram(name: "go", linkageName:
> > > > > > > > > > "_ZL2goi.__uniq.39558841650144213141281977295187289852",
> > > > > > > > > > scope: !8, file: !8, line: 7, type: !14, scopeLine: 8,
> > > > > > > > > > flags: DIFlagPrototyped, spFlags: DISPFlagLocalToUnit |
> > > > > > > > > > DISPFlagDefinition, unit: !0, retainedNodes: !2)`
> > > > > > > > > >
> > > > > > > > > > When I change `isUniqueInternalLinkageDecl()` to use
> > > > > > > > > > `!FD->getCanonicalDecl()->hasPrototype()`, I get the same
> > > > > > > > > > behavior with either ordering. When I run the full test
> > > > > > > > > > suite with that change, I get no test failures, so that may
> > > > > > > > > > be a reasonable fix worth investigating (I'm not super
> > > > > > > > > > familiar with the ins and outs of name mangling and whether
> > > > > > > > > > this change would be correct or not).
> > > > > > > > > Thanks so much, @aaron.ballman that does sound exactly like
> > > > > > > > > it summarizes the situation and the suggestion sounds like it
> > > > > > > > > could be the right thing.
> > > > > > > > >
> > > > > > > > > @hoy does that all make sense to you/could you try
> > > > > > > > > @aaron.ballman's suggested change/fix?
> > > > > > > > Thanks for doing the experiment @aaron.ballman . Actually for
> > > > > > > > the test in this diff, we would like the function `bar` to have
> > > > > > > > a unique linkage name. The suggested change doesn't seem to fix
> > > > > > > > that.
> > > > > > > >
> > > > > > > > ```
> > > > > > > > // bar should not be given a uniquefied name under
> > > > > > > > -funique-internal-linkage-names,
> > > > > > > > // since it doesn't come with valid prototype.
> > > > > > > > static int bar(a) int a;
> > > > > > > > {
> > > > > > > > return glob + a;
> > > > > > > > }
> > > > > > > >
> > > > > > > > ```
> > > > > > > I assume that comment was more written to describe existing
> > > > > > > practice than some intentional approach to dealing with a
> > > > > > > function like this, yeah?
> > > > > > >
> > > > > > > The overloadable attribute seems to be able to mangle this
> > > > > > > function correctly - so I think that was my whole concern - that
> > > > > > > unique internal linkage names should, ideally, treat things the
> > > > > > > same as overloadable unless there's a reason these things are
> > > > > > > really different - which I don't know of any reason that they are.
> > > > > > >
> > > > > > > So this looks like it fixes that gap - by enabling unique
> > > > > > > internal linkage names to mangle this case the same way
> > > > > > > overloadable does?
> > > > > > Sorry for not making it clear. The suggested fix does not mangle
> > > > > > this case (function `bar`) while the overloadable attributes is
> > > > > > able to mangle it.
> > > > > Ah, right - thanks for clarifying/sorry for my misunderstanding!
> > > > `bar` is never given a prototype, so I can see why it wouldn't mangle
> > > > for you. Perhaps it mangles for `overloadable` because of
> > > > `ItaniumMangleContextImpl::shouldMangleCXXName()` checking for the
> > > > attribute and returning `true`?
> > > Yes, and I think `shouldMangleCXXName` returns true because of
> > > `FD->getType()->getAs<FunctionProtoType>()` is true in the `overloadable`
> > > case. I guess I still don't fully understand the subtle diversion between
> > > `FD->getType()->getAs<FunctionProtoType>()` and `FD->hasPrototype()`.
> > > Yes, and I think shouldMangleCXXName returns true because of
> > > FD->getType()->getAs<FunctionProtoType>() is true in the overloadable
> > > case.
> >
> > I don't think that's correct -- I think it returns true because of this:
> > https://github.com/llvm/llvm-project/blob/main/clang/lib/AST/ItaniumMangle.cpp#L657
> >
> > > I guess I still don't fully understand the subtle diversion between
> > > FD->getType()->getAs<FunctionProtoType>() and FD->hasPrototype().
> >
> > `FD->getType()->getAs<FunctionProtoType>()` is checking whether the given
> > instance of the declaration has a type with a prototype.
> > `FD->hasPrototype()` looks at whether the given instance has *or inherits*
> > a prototype. So `hasPrototype()` is looking in more places for the
> > prototype.
> Thanks for pointing it out. I meant to say `overloadable` is only allowed on
> functions with `getAs<FunctionProtoType>()` but not `hasPrototype`:
> https://github.com/llvm/llvm-project/blob/main/clang/lib/Sema/SemaDecl.cpp#L9825
>
> On the contrary, `isUniqueInternalLinkageDecl` and `CGDebugInfo` rely on
> `hasPrototype`. This subtle diversion causes function `bar` to be mangled
> differently. Even with `overloadable`, function bar has a different symbol
> linkage name and debug linkage name:
>
>
> ```
> _attribute__((overloadable))
> static int bar(a) int a;
> {
> return glob + a;
> }
>
> results in:
>
> define internal i32
> @_ZL3bari.__uniq.95397005697148547017947938379908873441(i32 %a)
>
> but not a debug linkage name
> !24 = distinct !DISubprogram(name: "bar", scope: !6, file: !6, line: 19,
> type: !25, scopeLine: 20, spFlags: DISPFlagLocalToUnit | DISPFlagDefinition,
> unit: !2, retainedNodes: !4)
> ```
>
>
> Thanks for pointing it out. I meant to say overloadable is only allowed on
> functions with getAs<FunctionProtoType>() but not hasPrototype:
> https://github.com/llvm/llvm-project/blob/main/clang/lib/Sema/SemaDecl.cpp#L9825
Ah, good to know -- I have no idea if that's intentional or not.
> On the contrary, isUniqueInternalLinkageDecl and CGDebugInfo rely on
> hasPrototype. This subtle diversion causes function bar to be mangled
> differently. Even with overloadable, function bar has a different symbol
> linkage name and debug linkage name:
Unfortunately, it's a bit too far outside of my experience to know what the
right answer is here. Sorry!
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