[PATCH] D159339: [urgent][CodeGen] First check the kind and then the llvm::Function properties.

[Vassil Vassilev via Phabricator via cfe-commits]

v.g.vassilev added inline comments.


================
Comment at: clang/lib/CodeGen/CodeGenModule.cpp:2389
   if (getTarget().getCXXABI().areMemberFunctionsAligned()) {
-    if (F->getPointerAlignment(getDataLayout()) < 2 && isa<CXXMethodDecl>(D))
+    if (isa<CXXMethodDecl>(D) && F->getPointerAlignment(getDataLayout()) < 2)
       F->setAlignment(std::max(llvm::Align(2), F->getAlign().valueOrOne()));
----------------
daltenty wrote:
> v.g.vassilev wrote:
> > daltenty wrote:
> > > Thanks for looking into this. 
> > > 
> > > It's not clear to me how this re-ordering ends up fixing things. Can you clarify what the uninitialized value was in this expression?
> > > 
> > > 
> > The issue happens only in Release builds (RelWithDebInfo, too). From what I was able to see it is somewhere in `F->getPointerAlignment`. My assumption was that we cannot rely on the full properties of `F` to be set unless it is the declaration kind we expected (similar to checking if a something is a nullptr and then probing its members). Secondly the `isa` check is likely to be the less expensive check anyway.
> > 
> > I saw the issue yesterday and dug into it for a while. However, I decided to insert a "fix" before the release which is in few days since the `isa` seems to the faster check anyway.
> Thanks, yeah thats kind of what I expected.  `F->getPointerAlignment()` is likely getting inlined into in to this callsite and we are inspecting uninitialized properties of the DataLayout. The weird part is I don't see why those properties of the DataLayout ever should be uninitialized, so I think there might be something more broken underneath this.
> 
> That said, this is definitely better than before as you say, so let's go ahead with this for the release and maybe I'll do some more digging in `getPointerAlignment`.
Sounds good. For better or worse that workaround might make the issue more subtle to debug next time it appears...


Repository:
  rC Clang

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  https://reviews.llvm.org/D159339/new/

https://reviews.llvm.org/D159339