[LLVMbugs] [Bug 10201] New: clang does not warn on va_arg(args, float)

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=10201

           Summary: clang does not warn on va_arg(args, float)
           Product: clang
           Version: trunk
          Platform: Macintosh
        OS/Version: MacOS X
            Status: NEW
          Severity: normal
          Priority: P
         Component: C++
        AssignedTo: unassignedclangbugs at nondot.org
        ReportedBy: jonathan.sauer at gmx.de
                CC: llvmbugs at cs.uiuc.edu, dgregor at apple.com


Please consider the following program:

/* From stdarg.h: */
typedef __builtin_va_list va_list;
#define va_arg(ap, type)    __builtin_va_arg(ap, type)


static void foo(va_list args)
{
    /* Should be <double> */
    va_arg(args, float);
}


When this is compiled using Apple's GCC 4.2, GCC outputs this:

$ gcc -S clang.c
clang.c: In function ‘void foo(__va_list_tag*)’:
clang.c:9: warning: ‘float’ is promoted to ‘double’ when passed through ‘...’
clang.c:9: warning: (so you should pass ‘double’ not ‘float’ to ‘va_arg’)
clang.c:9: note: if this code is reached, the program will abort


When compiled with clang r133415, on the other hand, no warning is printed,
even though the code still does not work:

$ clang -S clang.c


Background for this are ISO C99 6.5.2.2p6 and p7:

If the expression that denotes the called function has a type that does not
include a prototype, [...] arguments that have type float are promoted to
double. These are called the default argument promotions. 

[...] The ellipsis notation in a function prototype declarator causes argument
type conversion to stop after the last declared parameter. The default argument
promotions are performed on trailing arguments.

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