gcc-4.6.0-0.12.fc15.x86_64 breaks strcmp? (was: Re: gcc-4.6.0-0.11.fc15.x86_64 breaks strcmp?)

[Richard W.M. Jones]

On Mon, Mar 07, 2011 at 10:14:57AM -0500, Adam Jackson wrote:
> On 3/7/11 9:49 AM, Richard W.M. Jones wrote:
> >Compiling libguestfs using gcc-4.6.0-0.11.fc15.x86_64 gives lots of:
> >
> >error: assuming signed overflow does not occur when changing X +- C1
> >cmp C2 to X cmp C1 +- C2 [-Werror=strict-overflow]
> >
> >These seem to be associated with code that does 'if (strcmp (s1, s2)
> >== 0)'
> >
> >For example:
> >
> >dir.c: In function ‘do_rm_rf’: dir.c:59:7: error: assuming signed
> >overflow does not occur when changing X +- C1 cmp C2 to X cmp C1 +-
> >C2 [-Werror=strict-overflow]
> 
> I'm not able to repro this with -0.12.fc15.

Firstly, I have just installed -0.12 and I can reproduce it.

> If I had to guess,
> you've got a macro for strcmp somewhere that's making type
> assumptions.  What does the .i file look like if you compile with
> -save-temps ?

OK ... When you said that, I initially suspected gnulib (which I am
using in this code), but I cannot see gnulib doing any macros or
replacement of strcmp.

Below is how the failure line expands(!)

----------------------------------------------------------------------
  if ((__extension__ ({ size_t __s1_len, __s2_len; (__builtin_constant_p ((path)) && __builtin_constant_p (("/")) && (__s1_len = strlen ((path)), __s2_len = strlen (("/")), (!((size_t)(const void *)(((path)) + 1) - (size_t)(const void *)((path)) == 1) || __s1_len >= 4) && (!((size_t)(const void *)((("/")) + 1) - (size_t)(const void *)(("/")) == 1) || __s2_len >= 4)) ? __builtin_strcmp ((path), ("/")) : (__builtin_constant_p ((path)) && ((size_t)(const void *)(((path)) + 1) - (size_t)(const void *)((path)) == 1) && (__s1_len = strlen ((path)), __s1_len < 4) ? (__builtin_constant_p (("/")) && ((size_t)(const void *)((("/")) + 1) - (size_t)(const void *)(("/")) == 1) ? __builtin_strcmp ((path), ("/")) : (__extension__ ({ __const unsigned char *__s2 = (__const unsigned char *) (__const char *) (("/")); register int __result = (((__const unsigned char *) (__const char *) ((path)))[0] - __s2[0]); if (__s1_len > 0 && __result == 0) { __result = (((__const unsigned char *) (__const char *) ((path)))[1] - __s2[1]); if (__s1_len > 1 && __result == 0) { __result = (((__const unsigned char *) (__const char *) ((path)))[2] - __s2[2]); if (__s1_len > 2 && __result == 0) __result = (((__const unsigned char *) (__const char *) ((path)))[3] - __s2[3]); } } __result; }))) : (__builtin_constant_p (("/")) && ((size_t)(const void *)((("/")) + 1) - (size_t)(const void *)(("/")) == 1) && (__s2_len = strlen (("/")), __s2_len < 4) ? (__builtin_constant_p ((path)) && ((size_t)(const void *)(((path)) + 1) - (size_t)(const void *)((path)) == 1) ? __builtin_strcmp ((path), ("/")) : (__extension__ ({ __const unsigned char *__s1 = (__const unsigned char *) (__const char *) ((path)); register int __result = __s1[0] - ((__const unsigned char *) (__const char *) (("/")))[0]; if (__s2_len > 0 && __result == 0) { __result = (__s1[1] - ((__const unsigned char *) (__const char *) (("/")))[1]); if (__s2_len > 1 && __result == 0) { __result = (__s1[2] - ((__const unsigned char *) (__const char *) (("/")))[2]); if (__s2_len > 2 && __result == 0) __result = (__s1[3] - ((__const unsigned char *) (__const char *) (("/")))[3]); } } __result; }))) : __builtin_strcmp ((path), ("/"))))); }) == 0)) {
----------------------------------------------------------------------

Rich.

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