[LLVMbugs] [Bug 18727] New: Integer not passed correctly in vararg

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=18727

            Bug ID: 18727
           Summary: Integer not passed correctly in vararg
           Product: clang
           Version: trunk
          Hardware: PC
                OS: MacOS X
            Status: NEW
          Severity: normal
          Priority: P
         Component: LLVM Codegen
          Assignee: unassignedclangbugs at nondot.org
          Reporter: ishiura-compiler at ml.kwansei.ac.jp
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified

Clang 3.5 (based on LLVM 3.5svn) for x86_64 target miscompiles the following
code.

    $ cat error.c

    #include <stdarg.h>

    union U0 { long m0[2]; };
    union U1 { int m0; };
    struct S0 { int m0[5]; };

    struct S0 func(struct S0 x0, ... )
    {
        va_list ap;
        va_start(ap, x0);
        union U0 x1 = va_arg(ap, union U0);
        union U0 x2 = va_arg(ap, union U0);
        union U1 x3 = va_arg(ap, union U1);
        int x4 = va_arg(ap, int);
        va_end(ap);

        if( x4 != 1 ) { __builtin_abort(); }

        return x0;
    }

    int main(void)
    {
        struct S0 x0 = {{1,1,1,1,1}};
        union U0 x1 = {{1,1}};
        union U1 x2 = {1};
        func(x0, x1, x1, x2, x0.m0[0]);

        return 0;
    }

    $ clang error.c

    $ ./a.out
    Abort trap: 6

The value of x4 was 0 instead of 1.
There was no problem with an i686 target.

    $ clang -v
    clang version 3.5 (trunk 200763)
    Target: x86_64-apple-darwin13.0.0
    Thread model: posix

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