[Sema] Prevent crash while trying to merge types

[davide]

Summary

This fixes bug 23086.
__builtin_isnan(...) causes clang to crash in sema. The proposed patch is an attempt to fix.

[rsmith]

lib/Sema/SemaDecl.cpp

2988–2991 ↗

(On Diff #24336)

• This function should not return true without a diagnostic having been emitted.
• NewProto cannot be null here due to the check on line 2979.
• OldProto should not be null here due to the check on line 2978.

Perhaps the root cause of the problem is that we set the wrong value for hasPrototype up on line 1752? We should be checking whether the builtin type is in fact a FunctionProtoType rather than just assuming it is.

[davide]

Yes, thanks. That actually worked and passes the test suite.
Does the check look fine to you?

[rsmith]

Yes, this seems like a reasonable approach (please also include the testcase from your previous patch).

cfe/trunk/lib/Sema/SemaDecl.cpp

if (getLangOpts().CPlusPlus) {
     Parent = CLinkageDecl;
   }
 
   FunctionDecl *New = FunctionDecl::Create(Context,
                                            Parent,
                                            Loc, Loc, II, R, /*TInfo=*/nullptr,
                                            SC_Extern,
                                            false,
-                                           /*hasPrototype=*/true);
+                                           R->isFunctionProtoType());
   New->setImplicit();
 
   // Create Decl objects for each parameter, adding them to the
   // FunctionDecl.
   if (const FunctionProtoType *FT = dyn_cast<FunctionProtoType>(R)) {
     SmallVector<ParmVarDecl*, 16> Params;
     for (unsigned i = 0, e = FT->getNumParams(); i != e; ++i) {
       ParmVarDecl *parm =

cfe/trunk/test/Sema/crash-invalid-builtin.c

+// RUN: %clang_cc1 -triple=x86_64-apple-darwin -fsyntax-only -verify %s
+// PR23086
+
+__builtin_isinf(...); // expected-warning {{type specifier missing, defaults to 'int'}} expected-error {{ISO C requires a named parameter before '...'}} // expected-error {{conflicting types for '__builtin_isinf'}} // expected-note {{'__builtin_isinf' is a builtin with type 'int ()'}}