Clang 3.3 bug

a.c

#include <stdio.h>
#include <string.h>
#include <stdarg.h>

// This function is not actually called, but it must exist in a different compilation unit
int X_rank(int *rank);

static int ErrorHandlerX(int comm,int line,const char *fun,const char *file,const char *dir,int n,int p,const char *mess)
{
  int rank;

  if (comm != 0) X_rank(&rank);

  if (p) {                      // p==0 so this branch is not taken, but it must exist
    printf("%s!\n",mess);
  }
  printf("%s() line %d in %s%s\n",fun,line,dir,file);
  return(n);
}

// must not be static, must have all arguments, must be variadic
int ErrorX(int comm,int line,const char *func,const char *file,const char *dir,int n,int p,const char *mess,...)
{
  va_list args;
  char buf[1000];
  const char *lbuf = 0;

  // None of these branches should be taken
  if (!func) func = "User provided function";
  if (!file) file = "NOT THE FILE NAME";
  if (!dir) dir = " ";
  if (comm == 10) comm = 11;

  if (mess) {
    strcpy(buf,mess);
    lbuf = mess;
  }

  va_start(args,mess);
  va_end(args);

  return ErrorHandlerX(comm,line,func,file,dir,n,p,lbuf);
}

int main()
{
  ErrorX(0,__LINE__,__func__,__FILE__,"/dir/",75,0,"Irrelevant Message");
  return 0;
}

Makefile

CC = clang
CFLAGS = -Wall -Wextra -pedantic -std=c99 -O1 -g  # -O1 or higher needed

a.out : a.o xrank.o
	$(CC) -o $@ $^

xrank.c

int X_rank(int *rank) {
  *rank = 0;
  return 0;
}