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;
+}
+
+
----------------
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)
```
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D98799/new/
https://reviews.llvm.org/D98799
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