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:
> 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()`.
Repository:
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https://reviews.llvm.org/D98799/new/
https://reviews.llvm.org/D98799
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