[PATCH] D22057: Prevent devirtualization of calls to un-instantiated functions.

Sunil Srivastava via cfe-commits cfe-commits at lists.llvm.org
Wed Sep 7 17:11:09 PDT 2016

Sunil_Srivastava added inline comments.

Comment at: test/CodeGen/no-devirt.cpp:16
@@ +15,3 @@
+   if (a > 6) return data[a] ;      // Should not devirtualize
+   if (a > 4) return data.func1(a); // Should devirtualize
+   return data.func2(a);            // Should devirtualize
Quuxplusone wrote:
> This is a really dumb question from the peanut gallery, but, could you explain why these two cases (lines 15 and 16) should differ?  It really seems like both calls should be able to be devirtualized, because the compiler statically knows what they should call.
> I think you mention the difference between lines 15 and 16 here:
> > except, for some reason, when it is an operator and used with an operator syntax
> but you don't explain *why* the difference is desirable. Shouldn't we just fix that difference, then?
> Is your first fix (
> > The first fix will be in the front end to force the instantiation on virtual calls that are potentially devirtualizable.
> ) basically "fix the difference between lines 15 and 16", or is it talking about something else entirely?
AFAICS, The two cases (line 15 and 16) should not differ.

The first fix will "fix the difference between line 15 and 16". I have the change for that ready, but once we do that, there will be no way (known to me) of testing the second "fix". Hence the second "fix" is being proposed for commit before the first.


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