Unexpected warning (confused by non-zero safemalloc?)

I have:

$ clang --version
Debian clang version 3.4-1~exp1 (trunk) (based on LLVM 3.4)
Target: x86_64-pc-linux-gnu
Thread model: posix

*** 1:3.4~svn185715-1~exp1 0
   500 http://llvm.org/apt/wheezy/ llvm-toolchain-wheezy/main amd64 Packages

..and I'm trying to compile:

#include <stdint.h>
#include <string.h>
#include <stdlib.h>

void *smalloc(size_t size) {
    if (size == 0) {
        return malloc(1);
    } else {
        return malloc(size);

char *dupstr(const char *s) {
    const int len = strlen(s);
    char *p = smalloc(len + 1);
    strcpy(p, s);
    return p;

I get:

$ clang -Weverything --analyze -c misc.c
misc.c:16:5: warning: String copy function overflows destination buffer
    strcpy(p, s);
1 warning generated.

It appears to be confused by the presence of that "if (size == 0)"
block in smalloc. Basically any change to this code removes the warning,
although size <= 1 leaves it.

Is this a bug, or did I do something silly?

Code derived from https://github.com/FauxFaux/PuTTYTray/blob/next/misc.c#L516

Well, the assignment from a size_t into an int is silly... but there's
still an issue reported even if you fix that.

The analyzer sees two paths here: one where strlen(s)+1 == 0, and one
where strlen(s)+1 != 0. On the strlen(s)+1 == 0 path, you're copying
a string of length SIZE_MAX into a buffer of length 1, an overflow.

Of course, strlen(s) == SIZE_MAX is impossible because s would cover
the entire address-space... so it's possible the analyzer should be a
bit smarter here.