erichkeane added inline comments.
================
Comment at: clang/lib/CodeGen/CodeGenModule.cpp:2957
+ if (!AliasFunc) {
+ auto *IFunc = cast<llvm::GlobalIFunc>(GetOrCreateLLVMFunction(
+ AliasName, DeclTy, GD, /*ForVTable=*/false, /*DontDefer=*/true,
----------------
erichkeane wrote:
> I think we want this in GetOrCreateMultiVersionResolver, so that it gets
> created when the ifunc does. That way you just need a
> "FD->isCPUDispatchMultiVersion() || isCPUSpecificMultiVersion()" check inside
> the supportsIFunc branch.
After discussing this offline, I believe this is the right function to create
the alias. The motivating example is:
// TU1:
__attribute__((cpu_dispatch(a,b,c))) void foo(void);
// TU2:
extern void foo(void);
Currently, TU1 doesn't bother to emit the ifunc, because we've attached
emitting this to when this is referenced.
We made that choice because we expected TU2 to mark 'foo' as
cpu_dispatch/cpu_specific in SOME way. I believe that it is harmless to emit
the ifunc all the time, which this is attempting to do. However, this needs to
change the ifunc to have LinkOnceODR linkage in
GetOrCreateMultiVersionResolver, otherwise this can cause linker errors.
================
Comment at: clang/lib/CodeGen/CodeGenModule.cpp:2961
+ auto *GA = llvm::GlobalAlias::create(
+ DeclTy, 0, getFunctionLinkage(GD), AliasName, IFunc, &getModule());
+ const auto *D = GD.getDecl();
----------------
I think the alias always needs LinkOnceODR linkage, to match the (new) IFunc
linkage.
Repository:
rC Clang
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D67058/new/
https://reviews.llvm.org/D67058
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