[cond-optab, trunk] fold &f != 0 better
Richard Guenther
richard.guenther@gmail.com
Thu Apr 9 11:27:00 GMT 2009
On Thu, Apr 9, 2009 at 10:56 AM, Paolo Bonzini <bonzini@gnu.org> wrote:
> I noticed that a common failure on cond-optab (e500, m32r, mcore) was on
> pr27150-1.c. This is a failure to optimize
>
> int g(int f)
> {
> return (&f)!=0;
> }
>
> The reason is that there is more straight-line coding on cond-optab and
> this confuses combine, which is no longer able to optimize it. But I
> decided to treat it as a missed tree optimization, fixing it with the
> following patch.
>
> I tested that the modified testcase fails on cond-optab without the
> patch, and passes with it.
>
> Bootstrap/regtest in progress, ok for trunk when it finishes?
Comments below
> Paolo
>
> 2009-04-09 Paolo Bonzini <bonzini@gnu.org>
>
> * fold-const.c (tree_single_nonzero_warnv_p): Always treat decls
> for things others than variables or functions as nonzero.
>
> 2009-04-09 Paolo Bonzini <bonzini@gnu.org>
>
> * gcc.dg/pr27150-1.c: Change to a link test.
>
> Index: gcc/fold-const.c
> ===================================================================
> --- gcc/fold-const.c (branch cond-optab)
> +++ gcc/fold-const.c (working copy)
> @@ -15011,8 +15011,8 @@ tree_single_nonzero_warnv_p (tree t, boo
> return false;
>
> /* Weak declarations may link to NULL. */
> - if (VAR_OR_FUNCTION_DECL_P (base))
> - return !DECL_WEAK (base);
> + if (DECL_P (base))
> + return !VAR_OR_FUNCTION_DECL_P (base) || !DECL_WEAK (base);
Hmm, I think this misses && flag_delete_null_pointer_checks, otherwise
a VAR_DECL may be at address zero. I'm not sure if that would apply
for PARM_DECLs, LABEL_DECLs, etc.
Thus, the patch is ok if you add && flag_delete_null_pointer_checks to
the VAR_OR_FUNCTION_DECL_P case.
Thanks,
Richard.
> /* Constants are never weak. */
> if (CONSTANT_CLASS_P (base))
> Index: gcc/testsuite/gcc.dg/pr27150-1.c
> ===================================================================
> --- gcc/testsuite/gcc.dg/pr27150-1.c (branch cond-optab)
> +++ gcc/testsuite/gcc.dg/pr27150-1.c (working copy)
> @@ -1,7 +1,9 @@
> /* { dg-do compile } */
> /* { dg-options "-O2" } */
> +extern int link_error ();
> int g(int f)
> {
> - return (&f)!=0;
> + int a = ((&f)!=0);
> + if (a) link_error ();
> + return a;
> }
> -
>
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