[PATCH] D157385: [clang][CFG] Cleanup functions

[Timm Bäder via Phabricator via cfe-commits]

tbaeder marked 2 inline comments as done.
tbaeder added inline comments.


================
Comment at: clang/lib/Analysis/CFG.cpp:2113
+
+bool CFGBuilder::hasTrivialDestructor(VarDecl *VD) const {
   // Check for const references bound to temporary. Set type to pointee.
----------------
steakhal wrote:
> Can't this accept `const VarDecl*` instead? That way we could get rid of that `const_cast` above.
Yes, I just didn't want to modify the existing function signature.


================
Comment at: clang/test/Analysis/scopes-cfg-output.cpp:1473-1474
+// CHECK-NEXT:    3: F f __attribute__((cleanup(cleanup_F)));
+// CHECK-NEXT:    4: [B1.3].~F() (Implicit destructor)
+// CHECK-NEXT:    5: CleanupFunction (cleanup_F)
+// CHECK-NEXT:    6: CFGScopeEnd(f)
----------------
steakhal wrote:
> tbaeder wrote:
> > aaronpuchert wrote:
> > > Interesting test! But it seems CodeGen has them swapped: compiling this snippet with `clang -c -S -emit-llvm` I get
> > > ```lang=LLVM
> > > define dso_local void @_Z4testv() #0 personality ptr @__gxx_personality_v0 {
> > >   %1 = alloca %class.F, align 1
> > >   %2 = alloca ptr, align 8
> > >   %3 = alloca i32, align 4
> > >   invoke void @_Z9cleanup_FP1F(ptr noundef %1)
> > >           to label %4 unwind label %5
> > > 
> > > 4:                                                ; preds = %0
> > >   call void @_ZN1FD2Ev(ptr noundef nonnull align 1 dereferenceable(1) %1) #3
> > >   ret void
> > > 
> > > ; ...
> > > }
> > > ```
> > > So first cleanup, then destructor. This is with 17.0.0-rc2.
> > Interesting, I thought I checked this and used the correct order. Will re-check, thanks.
> I believe this demonstrates the wrong order I also spotted earlier.
The current code generates the given CFG, i.e. the cleanup function comes first, followed by the dtor:
```
 [B1]
   1: CFGScopeBegin(f)
   2:  (CXXConstructExpr, [B1.3], F)
   3: F f __attribute__((cleanup(f_)));
   4: CleanupFunction (f_)
   5: [B1.3].~F() (Implicit destructor)
   6: CFGScopeEnd(f)
   Preds (1): B2
   Succs (1): B0
```

(The comment from Aaron is from before when I had the order swapped.)


================
Comment at: clang/test/Analysis/scopes-cfg-output.cpp:1480
+public:
+  ~F() {}
+};
----------------
steakhal wrote:
> aaronpuchert wrote:
> > tbaeder wrote:
> > > aaronpuchert wrote:
> > > > As with the cleanup function, a definition shouldn't be necessary.
> > > Is there a way to test whether the contents of the cleanup function are being checked as well? From these tests, I only know we consider them called, but not whether we (properly) analyze their bodies in the context as well. Or is that separate from this patch?
> > For now we're just adding a new element to the CFG and adapting the respective tests. The CFG is generated on a per-function basis, and the generation of one function's CFG will never look into another function's body. It might use some (declaration) properties of course, like whether it has `[[noreturn]]` or `noexcept`. Of course we should also generate a CFG for the cleanup function, but that's independent of this change.
> > 
> > Users of the CFG will naturally need to be taught about this new element type to “understand” it. Otherwise they should simply skip it. Since the CFG previously did not contain such elements, there should be no change for them. So we can also initially just add the element and not tell anybody about it.
> > 
> > We could also add understanding of the new element type to other CFG users, but you don't have to do this. If you only care about Thread Safety Analysis, then it's totally fine to handle it only there.
> > 
> > But let's move all changes to Thread Safety Analysis into a follow-up, so that we don't have to bother the CFG maintainers with that.
> Speaking of `noreturn`, I think it is worth demonstrating that if the cleanup function has `noreturn` attribute, then the dtor is not called.
Yeah, that does not work correctly right now.


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D157385/new/

https://reviews.llvm.org/D157385