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:
> > > 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.
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