[PATCH] D66094: [CodeGen] Emit destructor calls for non-trivial C structs returned by function calls and loaded from volatile objects

[John McCall via Phabricator via cfe-commits]

rjmccall added inline comments.


================
Comment at: clang/lib/Sema/SemaExpr.cpp:677
+      E->getType().isDestructedType() == QualType::DK_nontrivial_c_struct)
+    Cleanup.setExprNeedsCleanups(true);
+
----------------
ahatanak wrote:
> rjmccall wrote:
> > ahatanak wrote:
> > > rjmccall wrote:
> > > > Why only when the l-value is volatile?
> > > I was trying to avoid emitting `ExprWithCleanups` when it wasn't needed and it seemed that it wasn't needed for non-volatile types. I'm not sure it's important, so I've removed the check for volatile. Also, `ExprWithCleanups` shouldn't' be emitted when this is in file scope, so I fixed that too.
> > Hmm, not sure about this file-scope thing, since the combination of C++ dynamic initializers and statement-expressions means  we can have pretty unrestricted code there.
> I should have explained why this was needed, but I wanted to prevent emitting `ExprWithCleanups` in the following example:
> 
> ```
> struct A {
>   id f0;
> };
> 
> typedef struct A A;
> 
> A g = (A){ .f0 = 0 };
> ```
> 
> The l-value to r-value conversion happens here because compound literals are l-values. Since `g` is a global of a non-trivial C struct type, we shouldn't try to push a cleanup and destruct the object.
> 
> We don't have to think about the C++ case since the line below checks the type is a non-trivial C type. I didn't think about statement expressions, but they aren't allowed in file scope, so I guess that's not a problem either.
I would hope that the constant-evaluator here might be smart enough to ignore some elidable temporaries.


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D66094/new/

https://reviews.llvm.org/D66094