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