r281632 - Reapply: Silence false positive diagnostics regarding passing an object of enumeration type to va_start().

[Aaron Ballman via cfe-commits]

Author: aaronballman
Date: Thu Sep 15 13:07:51 2016
New Revision: 281632

URL: http://llvm.org/viewvc/llvm-project?rev=281632&view=rev
Log:
Reapply: Silence false positive diagnostics regarding passing an object of enumeration type to va_start().

The underlying type for an enumeration in C is either char, signed int, or unsigned int. In the case the underlying type is chosen to be char (such as when passing -fshort-enums or using __attribute__((packed)) on the enum declaration), the enumeration can result in undefined behavior. However, when the underlying type is signed int or unsigned int (or long long as an extension), there is no undefined behavior because the types are compatible. This patch silences diagnostics for the latter while retaining the diagnostics for the former.

This patch addresses PR29140.

Modified:
    cfe/trunk/lib/Sema/SemaChecking.cpp
    cfe/trunk/test/Sema/varargs.c

Modified: cfe/trunk/lib/Sema/SemaChecking.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Sema/SemaChecking.cpp?rev=281632&r1=281631&r2=281632&view=diff
==============================================================================
--- cfe/trunk/lib/Sema/SemaChecking.cpp (original)
+++ cfe/trunk/lib/Sema/SemaChecking.cpp Thu Sep 15 13:07:51 2016
@@ -3240,8 +3240,17 @@ bool Sema::SemaBuiltinVAStartImpl(CallEx
     Diag(TheCall->getArg(1)->getLocStart(),
          diag::warn_second_arg_of_va_start_not_last_named_param);
   else if (IsCRegister || Type->isReferenceType() ||
-           Type->isPromotableIntegerType() ||
-           Type->isSpecificBuiltinType(BuiltinType::Float)) {
+           Type->isSpecificBuiltinType(BuiltinType::Float) || [=] {
+             // Promotable integers are UB, but enumerations need a bit of
+             // extra checking to see what their promotable type actually is.
+             if (!Type->isPromotableIntegerType())
+               return false;
+             if (!Type->isEnumeralType())
+               return true;
+             const EnumDecl *ED = Type->getAs<EnumType>()->getDecl();
+             return !(ED &&
+                      Context.typesAreCompatible(ED->getPromotionType(), Type));
+           }()) {
     unsigned Reason = 0;
     if (Type->isReferenceType())  Reason = 1;
     else if (IsCRegister)         Reason = 2;

Modified: cfe/trunk/test/Sema/varargs.c
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/Sema/varargs.c?rev=281632&r1=281631&r2=281632&view=diff
==============================================================================
--- cfe/trunk/test/Sema/varargs.c (original)
+++ cfe/trunk/test/Sema/varargs.c Thu Sep 15 13:07:51 2016
@@ -1,5 +1,6 @@
-// RUN: %clang_cc1 -fsyntax-only -verify %s
+// RUN: %clang_cc1 -fsyntax-only -verify %s -triple i386-pc-unknown
 // RUN: %clang_cc1 -fsyntax-only -verify %s -triple x86_64-apple-darwin9
+// RUN: %clang_cc1 -fsyntax-only -fms-compatibility -DMS -verify %s -triple x86_64-pc-win32
 
 void f1(int a)
 {
@@ -94,3 +95,20 @@ void f12(register int i, ...) {  // expe
   __builtin_va_start(ap, i); // expected-warning {{passing a parameter declared with the 'register' keyword to 'va_start' has undefined behavior}}
   __builtin_va_end(ap);
 }
+
+enum __attribute__((packed)) E1 {
+  one1
+};
+
+void f13(enum E1 e, ...) {
+  __builtin_va_list va;
+  __builtin_va_start(va, e);
+#ifndef MS
+  // In Microsoft compatibility mode, all enum types are int, but in
+  // non-ms-compatibility mode, this enumeration type will undergo default
+  // argument promotions.
+  // expected-note at -7 {{parameter of type 'enum E1' is declared here}}
+  // expected-warning at -6 {{passing an object that undergoes default argument promotion to 'va_start' has undefined behavior}}
+#endif
+  __builtin_va_end(va);
+}