PR20958: Allow __builtin_isnan to be declared.

[• chatur01]

Summary

Before this patch, a builtin which takes only a variadic argument,
such as,

int __builtin_isnan(...);

Was actually getting declared as,

int __builtin_isnan();

Tis was causing several problem, one is described in PR20958. The
special-casing of this variadic argument has been removed. It
uncovered MS's __noop builtin was incorrectly handled. We don't care
about the semantics of those arguments, so the builtin definition for
it has been updated as such.

A further wart exposed here was the declaration of vfprintf to appease
autoconf. That has been reverted. What was once an error about
requiring inclusion of a header has now been downgraded to a warning,
so the reason for that fix is no longer valid. See PR4290 and r72760.

[• chatur01]

I have a different approach to handling this behaviour that I will submit soon.

include/clang/Basic/Builtins.def

 LANGBUILTIN(__GetExceptionInfo, "v*.", "ntu", ALL_MS_LANGUAGES)
 LANGBUILTIN(_InterlockedCompareExchange, "LiLiD*LiLi", "n", ALL_MS_LANGUAGES)
 LANGBUILTIN(_InterlockedCompareExchangePointer, "v*v*D*v*v*", "n", ALL_MS_LANGUAGES)
 LANGBUILTIN(_InterlockedDecrement,       "LiLiD*",     "n", ALL_MS_LANGUAGES)
 LANGBUILTIN(_InterlockedExchangeAdd,     "LiLiD*Li",   "n", ALL_MS_LANGUAGES)
 LANGBUILTIN(_InterlockedExchange,        "LiLiD*Li",   "n", ALL_MS_LANGUAGES)
 LANGBUILTIN(_InterlockedExchangePointer, "v*v*D*v*",   "n", ALL_MS_LANGUAGES)
 LANGBUILTIN(_InterlockedIncrement,       "LiLiD*",     "n", ALL_MS_LANGUAGES)
-LANGBUILTIN(__noop,           "i.",  "n", ALL_MS_LANGUAGES)
+LANGBUILTIN(__noop,           "i.",  "nt", ALL_MS_LANGUAGES)
 LANGBUILTIN(__readfsdword,    "ULiULi", "n", ALL_MS_LANGUAGES)
 LANGBUILTIN(__va_start,       "vc**.", "nt", ALL_MS_LANGUAGES)
 
 // Microsoft library builtins.
 LIBBUILTIN(_setjmpex, "iJ", "fj",   "setjmpex.h", ALL_MS_LANGUAGES)
 
 // C99 library functions
 // C99 stdlib.h

 LIBBUILTIN(strerror, "c*i",       "f",     "string.h", ALL_LANGUAGES)
 LIBBUILTIN(strlen, "zcC*",        "f",     "string.h", ALL_LANGUAGES)
 // C99 stdio.h
 LIBBUILTIN(printf, "icC*.",       "fp:0:", "stdio.h", ALL_LANGUAGES)
 LIBBUILTIN(fprintf, "iP*cC*.",    "fp:1:", "stdio.h", ALL_LANGUAGES)
 LIBBUILTIN(snprintf, "ic*zcC*.",  "fp:2:", "stdio.h", ALL_LANGUAGES)
 LIBBUILTIN(sprintf, "ic*cC*.",    "fp:1:", "stdio.h", ALL_LANGUAGES)
 LIBBUILTIN(vprintf, "icC*a",      "fP:0:", "stdio.h", ALL_LANGUAGES)
-LIBBUILTIN(vfprintf, "i.",        "fP:1:", "stdio.h", ALL_LANGUAGES)
+LIBBUILTIN(vfprintf, "iP*cC*a",   "fP:1:", "stdio.h", ALL_LANGUAGES)
 LIBBUILTIN(vsnprintf, "ic*zcC*a", "fP:2:", "stdio.h", ALL_LANGUAGES)
 LIBBUILTIN(vsprintf, "ic*cC*a",   "fP:1:", "stdio.h", ALL_LANGUAGES)
 LIBBUILTIN(scanf, "icC*R.",       "fs:0:", "stdio.h", ALL_LANGUAGES)
 LIBBUILTIN(fscanf, "iP*RcC*R.",   "fs:1:", "stdio.h", ALL_LANGUAGES)
 LIBBUILTIN(sscanf, "icC*RcC*R.",  "fs:1:", "stdio.h", ALL_LANGUAGES)
 LIBBUILTIN(vscanf, "icC*Ra",      "fS:0:", "stdio.h", ALL_LANGUAGES)
 LIBBUILTIN(vfscanf, "iP*RcC*Ra",  "fS:1:", "stdio.h", ALL_LANGUAGES)
 LIBBUILTIN(vsscanf, "icC*RcC*Ra", "fS:1:", "stdio.h", ALL_LANGUAGES)

lib/AST/ASTContext.cpp

QualType ASTContext::GetBuiltinType(unsigned Id,
   assert((TypeStr[0] != '.' || TypeStr[1] == 0) &&
          "'.' should only occur at end of builtin type list!");
 
   FunctionType::ExtInfo EI(CC_C);
   if (BuiltinInfo.isNoReturn(Id)) EI = EI.withNoReturn(true);
 
   bool Variadic = (TypeStr[0] == '.');
 
-  // We really shouldn't be making a no-proto type here, especially in C++.
-  if (ArgTypes.empty() && Variadic)
-    return getFunctionNoProtoType(ResType, EI);
-
   FunctionProtoType::ExtProtoInfo EPI;
   EPI.ExtInfo = EI;
   EPI.Variadic = Variadic;
 
   return getFunctionType(ResType, ArgTypes, EPI);
 }
 
 static GVALinkage basicGVALinkageForFunction(const ASTContext &Context,

test/Sema/vfprintf-invalid-redecl.c

 // RUN: %clang_cc1 %s -fsyntax-only -verify
 // PR4290
 
 // The following declaration is not compatible with vfprintf(), but make
 // sure this isn't an error: autoconf expects this to build.
-char vfprintf(); // expected-warning {{incompatible redeclaration of library function 'vfprintf'}} expected-note {{'vfprintf' is a builtin}}
+char vfprintf(); // expected-warning {{declaration of built-in function 'vfprintf' requires inclusion of the header <stdio.h>}}

test/Sema/vfprintf-valid-redecl.c

 // RUN: %clang_cc1 %s -fsyntax-only -pedantic -verify
-// RUN: %clang_cc1 %s -fsyntax-only -pedantic -verify -DPREDECLARE
-// expected-no-diagnostics
+// RUN: %clang_cc1 %s -fsyntax-only -pedantic -DPREDECLARE
 
 #ifdef PREDECLARE
 // PR16344
 // Clang has defined 'vfprint' in builtin list. If the following line occurs before any other
 // `vfprintf' in this file, and we getPreviousDecl()->getTypeSourceInfo() on it, then we will
 // get a null pointer since the one in builtin list doesn't has valid TypeSourceInfo.
 int vfprintf(void) { return 0; }
 #endif
 
 // PR4290
-// The following declaration is compatible with vfprintf, so we shouldn't
-// warn.
-int vfprintf();
+// The following declaration is compatible with vfprintf, so it should not be an error.
+int vfprintf(); // expected-warning {{declaration of built-in function 'vfprintf' requires inclusion of the header <stdio.h>}}