[Verifier] Restore defined-resolver verification for IFuncs

[ibookstein]

Summary

Now that clang no longer emits GlobalIFunc-s with a
declaration for a resolver, we can restore that check.
In addition, add a linkage check like the one we have
on GlobalAlias-es, and a Verifier test for ifuncs.

Signed-off-by: Itay Bookstein <[e-mail]>

[ibookstein]

clang-format

[MaskRay]

I know little about the depended cpudispatch patch. This one looks good.

llvm/lib/IR/Verifier.cpp

843

[ibookstein]

Update description, rebase, rerun CI.

[ibookstein]

Add verifier test for ifuncs.

[ibookstein]

add another test with available_externally resolver

llvm/include/llvm/IR/GlobalIFunc.h

Function *getResolverFunction() {
     return const_cast<Function *>(
         static_cast<const GlobalIFunc *>(this)->getResolverFunction());
   }
 
   static FunctionType *getResolverFunctionType(Type *IFuncValTy) {
     return FunctionType::get(IFuncValTy->getPointerTo(), false);
   }
 
+  static bool isValidLinkage(LinkageTypes L) {
+    return isExternalLinkage(L) || isLocalLinkage(L) || isWeakLinkage(L) ||
+           isLinkOnceLinkage(L);
+  }
+
   // Methods for support type inquiry through isa, cast, and dyn_cast:
   static bool classof(const Value *V) {
     return V->getValueID() == Value::GlobalIFuncVal;
   }
 };
 
 template <>
 struct OperandTraits<GlobalIFunc>
     : public FixedNumOperandTraits<GlobalIFunc, 1> {};
 
 DEFINE_TRANSPARENT_OPERAND_ACCESSORS(GlobalIFunc, Constant)
 
 } // end namespace llvm
 
 #endif // LLVM_IR_GLOBALIFUNC_H

llvm/lib/IR/Verifier.cpp

Assert(isa<GlobalValue>(Aliasee) || isa<ConstantExpr>(Aliasee),
          "Aliasee should be either GlobalValue or ConstantExpr", &GA);
 
   visitAliaseeSubExpr(GA, *Aliasee);
 
   visitGlobalValue(GA);
 }
 
 void Verifier::visitGlobalIFunc(const GlobalIFunc &GI) {
+  Assert(GlobalIFunc::isValidLinkage(GI.getLinkage()),
+         "IFunc should have private, internal, linkonce, weak, linkonce_odr, "
+         "weak_odr, or external linkage!", &GI);
   // Pierce through ConstantExprs and GlobalAliases and check that the resolver
-  // has a Function 
+  // is a Function definition
   const Function *Resolver = GI.getResolverFunction();
   Assert(Resolver, "IFunc must have a Function resolver", &GI);
+  Assert(!Resolver->isDeclarationForLinker(),
+         "IFunc resolver must be a definition", &GI);
 
   // Check that the immediate resolver operand (prior to any bitcasts) has the
   // correct type
   const Type *ResolverTy = GI.getResolver()->getType();
   const Type *ResolverFuncTy =
       GlobalIFunc::getResolverFunctionType(GI.getValueType());
   Assert(ResolverTy == ResolverFuncTy->getPointerTo(),
          "IFunc resolver has incorrect type", &GI);