rjmccall added inline comments.
================
Comment at: include/clang/Driver/Options.td:990
@@ -988,2 +989,3 @@
"value range">;
+def fstrict_vptrs: Flag<["-"], "fstrict-vptrs">, Group<f_Group>,
Flags<[CC1Option]>;
def fstrict_overflow : Flag<["-"], "fstrict-overflow">, Group<f_Group>;
----------------
This needs documentation for the --help output, something like "Enable
optimizations based on the strict rules for overwriting polymorphic C++
objects".
This option should eventually be promoted to be a driver option, so we might as
well figure out the name now. I'd rather not introduce "vptr" to the user
lexicon. I suggest -fstrict-vtable-pointers.
================
Comment at: lib/CodeGen/CGClass.cpp:1279
@@ +1278,3 @@
+ if (CGM.getCodeGenOpts().StrictVPtrs && BaseVPtrsInitialized)
+ CXXThisValue = Builder.CreateInvariantGroupBarrier(LoadCXXThis());
+
----------------
Prazek wrote:
> rjmccall wrote:
> > Should this just be in InitializeVTablePointers?
> I want to add invariant.group.barrier only if it's needed. F.e. I don't want
> to put before I initialize vptrs for base, or when my class doesn't inherit
> frome anything. I want emit barrier after I will initialize some other vptrs.
>
> InitializeVptrs is called in EmitBaseInitializer, and also I woudnt want to
> put some extra flag if it must produce barrier or not (because it is hard to
> distinguish it from inside)
Fair enough.
Do we need to emit these barriers in unoptimized builds?
================
Comment at: lib/CodeGen/CGClass.cpp:1487
@@ +1486,3 @@
+ if (!CanSkipVTablePointerInitialization(getContext(), Dtor)) {
+ // Inserting llvm.invariant.group.barrier intrinsic before base vptrs
+ // initialization to stop propagating previous vptr value.
----------------
Grammar: "Insert the llvm.invariant.group.barrier intrinsic before initializing
the vptrs to cancel any previous assumptions we might have made."
http://reviews.llvm.org/D12312
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