[clang][Interp] Fix comparing to integral function pointers

We need to account for the fact that the Function pointer is not
accessible here. Add FunctionPointer::isWeak() for that.

Author: tbaederr

clang/lib/AST/Interp/FunctionPointer.h

@@ -32,6 +32,12 @@ class FunctionPointer final {
 
   const Function *getFunction() const { return Func; }
   bool isZero() const { return !Func; }
+  bool isWeak() const {
+    if (!Func || !Valid)
+      return false;
+
+    return Func->getDecl()->isWeak();
+  }
 
   APValue toAPValue() const {
     if (!Func)

clang/lib/AST/Interp/Interp.h

@@ -758,7 +758,7 @@ inline bool CmpHelperEQ<FunctionPointer>(InterpState &S, CodePtr OpPC,
 
   // We cannot compare against weak declarations at compile time.
   for (const auto &FP : {LHS, RHS}) {
-    if (!FP.isZero() && FP.getFunction()->getDecl()->isWeak()) {
+    if (FP.isWeak()) {
       const SourceInfo &Loc = S.Current->getSource(OpPC);
       S.FFDiag(Loc, diag::note_constexpr_pointer_weak_comparison)
           << FP.toDiagnosticString(S.getCtx());

clang/test/AST/Interp/c.c

@@ -1,7 +1,7 @@
 // RUN: %clang_cc1 -triple x86_64-linux -fexperimental-new-constant-interpreter -verify=expected,all -std=c11 -Wcast-qual %s
-// RUN: %clang_cc1 -triple x86_64-linux -fexperimental-new-constant-interpreter -pedantic -verify=pedantic-expected,all -std=c11 -Wcast-qual %s
+// RUN: %clang_cc1 -triple x86_64-linux -fexperimental-new-constant-interpreter -pedantic -verify=pedantic,pedantic-expected,all -std=c11 -Wcast-qual %s
 // RUN: %clang_cc1 -triple x86_64-linux -verify=ref,all -std=c11 -Wcast-qual %s
-// RUN: %clang_cc1 -triple x86_64-linux -pedantic -verify=pedantic-ref,all -std=c11 -Wcast-qual %s
+// RUN: %clang_cc1 -triple x86_64-linux -pedantic -verify=pedantic,pedantic-ref,all -std=c11 -Wcast-qual %s
 
 typedef __INTPTR_TYPE__ intptr_t;
 typedef __PTRDIFF_TYPE__ ptrdiff_t;
@@ -227,3 +227,9 @@ int castViaInt[*(int*)(unsigned long)"test"]; // ref-error {{variable length arr
                                               // pedantic-ref-error {{variable length array}} \
                                               // expected-error {{variable length array}} \
                                               // pedantic-expected-error {{variable length array}}
+
+const void (*const funcp)(void) = (void*)123; // pedantic-warning {{converts between void pointer and function pointer}}
+_Static_assert(funcp == (void*)0, ""); // all-error {{failed due to requirement 'funcp == (void *)0'}} \
+                                       // pedantic-warning {{expression is not an integer constant expression}}
+_Static_assert(funcp == (void*)123, ""); // pedantic-warning {{equality comparison between function pointer and void pointer}} \
+                                         // pedantic-warning {{expression is not an integer constant expression}}