Verifier: Check ifunc resolver functions return a pointer

[arsenm]

Summary

Clang and gcc both reject trying to use ifunc with a function which
doesn't return a pointer type. Some opaque pointer tests were using
this, apparently by accident.

[arsenm]

fe466887d1bd9a68fa2f82fda3b33b7a619c6082

llvm/lib/IR/Verifier.cpp

void Verifier::visitGlobalIFunc(const GlobalIFunc &GI) {
   const Function *Resolver = GI.getResolverFunction();
   Check(Resolver, "IFunc must have a Function resolver", &GI);
   Check(!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();
+
+  Check(isa<PointerType>(Resolver->getFunctionType()->getReturnType()),
+        "IFunc resolver must return a pointer", &GI);
+
   const Type *ResolverFuncTy =
       GlobalIFunc::getResolverFunctionType(GI.getValueType());
   Check(ResolverTy == ResolverFuncTy->getPointerTo(GI.getAddressSpace()),
         "IFunc resolver has incorrect type", &GI);
 }
 
 void Verifier::visitNamedMDNode(const NamedMDNode &NMD) {
   // There used to be various other llvm.dbg.* nodes, but we don't support

llvm/test/Assembler/opaque-ptr-struct-types.ll

 %T4 = type { i8 }
 %T5 = type { i8 }
 %T6 = type { i8 }
 %T7 = type { i8 }
 %T8 = type { i8 }
 
 @g = external global %T1
 
[e-mail] = ifunc %T8 (), ptr @f
[e-mail] = ifunc %T8 (), ptr @f.resolver
 
 define %T2 @f(ptr %p) {
   alloca %T3
   getelementptr %T4, ptr %p, i64 1
   call void @f(ptr sret(%T5) %p)
   store ptr getelementptr (%T6, ptr @g, i64 1), ptr %p
   unreachable
 }
 
+define %T2* @f.resolver(ptr %p) {
+  alloca %T3
+  getelementptr %T4, ptr %p, i64 1
+  call void @f(ptr sret(%T5) %p)
+  store ptr getelementptr (%T6, ptr @g, i64 1), ptr %p
+  unreachable
+}
+
 declare void @f2(ptr sret(%T7))

llvm/test/Other/force-opaque-ptrs.ll

 
 ; CHECK: @ga = alias i18, ptr @g2
 @g2 = global i18 0
 @ga = alias i18, i18* @g2
 
 ; CHECK: @ga2 = alias i19, ptr @g2
 @ga2 = alias i19, i19* bitcast (i18* @g2 to i19*)
 
-; CHECK: @gi = ifunc i20 (), ptr @f
-@gi = ifunc i20 (), i20 ()* ()* bitcast (void (i32*)* @f to i20 ()* ()*)
+; CHECK: @gi = ifunc i20 (), ptr @resolver
+@gi = ifunc i20 (), i20 ()* ()* bitcast (i32* ()* @resolver to i20 ()* ()*)
+
+
+define i32* @resolver() {
+  %load = load i32, i32* @g.fwd
+  %ptr = inttoptr i32 %load to i32*
+  ret i32* %ptr
+}
 
 define void @f(i32* %p) {
 ; CHECK-LABEL: define {{[^@]+}}@f
 ; CHECK-SAME: (ptr [[P:%.*]]) {
 ; CHECK-NEXT:    [[A:%.*]] = alloca i17, align 4
 ; CHECK-NEXT:    call void @fn.fwd(i32 0)
 ; CHECK-NEXT:    store i32 0, ptr @g.fwd, align 4
 ; CHECK-NEXT:    ret void

llvm/test/Verifier/ifunc.ll

 }
 @inval_resolver_decl2 = ifunc void (), void ()* ()* @resolver_linker_decl
 ; CHECK: IFunc resolver must be a definition
 ; CHECK-NEXT: @inval_resolver_decl2
 
 @inval_resolver_type = ifunc i32 (), void ()* ()* @resolver
 ; CHECK: IFunc resolver has incorrect type
 ; CHECK-NEXT: @inval_resolver_type
+
+@ifunc_nonpointer_return_type = ifunc i32 (), i32 ()* @resolver_returns_nonpointer
+; CHECK: IFunc resolver must return a pointer
+; CHECK-NEXT: i32 ()* @ifunc_nonpointer_return_type
+
+define i32 @resolver_returns_nonpointer() {
+  ret i32 0
+}