On Sun, Jan 31, 2021 at 02:12:46PM +0100, Jakub Jelinek via Gcc-patches wrote:
> On Sun, Jan 31, 2021 at 01:49:29PM +0100, Eric Botcazou wrote:
> > > The important difference is for strn{,case}cmp folding, we pass that s2
> > > value as the last argument to the host functions comparing the c_getstr
> > > results. If s2 fits into size_t, then my patch makes no difference,
> > > but if it is larger, we know the 2 c_getstr objects need to fit into the
> > > host address space, so larger s2 should just act essentially as strcmp
> > > or strcasecmp; as none of those objects can occupy 100% of the address
> > > space, using MIN (SIZE_MAX, s2) achieves that.
> >
> > But SIZE_MAX is a host value, isn't it? As a matter of fact, it breaks the
>
> Sure.
>
> > build with somewhat ancient glibcs:
> >
> > In file included from ../../src/gcc/fold-const-call.c:21:
> >
> > ../../src/gcc/fold-const-call.c: In function 'tree_node*
> > fold_const_call(combined_fn, tree, tree, tree, tree)':
> >
> > ../../src/gcc/fold-const-call.c:1777:56: error: 'SIZE_MAX' was not declared
> > in
> > this scope
> >
> > 1777 | return build_int_cst (type, strncmp (p0, p1, MIN (s2, SIZE_MAX)));
> >
> > because /usr/include/stdint.h has:
> >
> > /* The ISO C99 standard specifies that in C++ implementations these
> > macros should only be defined if explicitly requested. */
> > #if !defined __cplusplus || defined __STDC_LIMIT_MACROS
>
> Ugh. Anyway, we don't really need the SIZE_MAX macro, we can use
> INTTYPE_MAXIMUM (size_t) or (~(size_t) 0) too instead of it.
In patch form now (for ~ we'd need to use (size_t) ~(size_t) 0 to be
fully portable, I think nothing in the standard requires that size_t isn't
e.g. unsigned char or unsigned short that would then promote to int.
Ok for trunk?
2021-01-31 Jakub Jelinek <ja...@redhat.com>
* fold-const-call.c (fold_const_call): Use INTTYPE_MAXIMUM (size_t)
instead of SIZE_MAX.
--- gcc/fold-const-call.c.jj 2021-01-25 10:03:30.855413068 +0100
+++ gcc/fold-const-call.c 2021-01-31 18:37:04.022539076 +0100
@@ -1777,7 +1777,9 @@ fold_const_call (combined_fn fn, tree ty
&& !TREE_SIDE_EFFECTS (arg1))
return build_int_cst (type, 0);
else if ((p0 = c_getstr (arg0)) && (p1 = c_getstr (arg1)))
- return build_int_cst (type, strncmp (p0, p1, MIN (s2, SIZE_MAX)));
+ return build_int_cst (type,
+ strncmp (p0, p1,
+ MIN (s2, INTTYPE_MAXIMUM (size_t))));
return NULL_TREE;
case CFN_BUILT_IN_STRNCASECMP:
@@ -1789,7 +1791,7 @@ fold_const_call (combined_fn fn, tree ty
return build_int_cst (type, 0);
else if ((p0 = c_getstr (arg0))
&& (p1 = c_getstr (arg1))
- && strncmp (p0, p1, MIN (s2, SIZE_MAX)) == 0)
+ && strncmp (p0, p1, MIN (s2, INTTYPE_MAXIMUM (size_t))) == 0)
return build_int_cst (type, 0);
return NULL_TREE;
Jakub
