On Mon, 1 Dec 2014, Marc Glisse wrote:
> On Mon, 1 Dec 2014, Richard Biener wrote:
>
> > The following fixes the oldest bug in my list of assigned PRs, namely
> > combining A / CST / CST' to A / (CST * CST'). extract_muldiv does
> > this in fold-const.c (but it fails to optimize to zero when CST * CST'
> > overflows).
> >
> > Bootstrapped and tested on x86_64-unknown-linux-gnu, applied to trunk.
> >
> > Richard.
> >
> > 2014-12-01 Richard Biener <rguent...@suse.de>
> >
> > PR tree-optimization/15346
> > * Makefile.in (gimple-match.o-warn): Remove -Wno-unused-parameter,
> > add -Wno-unused-but-set-variable.
> > * match.pd: Combine two successive divisions.
> >
> > * gcc.dg/tree-ssa/forwprop-32.c: New testcase.
> >
> > Index: gcc/match.pd
> > ===================================================================
> > --- gcc/match.pd (revision 218140)
> > +++ gcc/match.pd (working copy)
> > @@ -129,6 +129,19 @@ (define_operator_list inverted_tcc_compa
> > && TYPE_UNSIGNED (type))
> > (trunc_div @0 @1)))
> >
> > +/* Combine two successive divisions. */
> > +(for div (trunc_div ceil_div floor_div round_div exact_div)
> > + (simplify
> > + (div (div @0 INTEGER_CST@1) INTEGER_CST@2)
> > + (with {
> > + bool overflow_p;
> > + wide_int mul = wi::mul (@1, @2, TYPE_SIGN (type), &overflow_p);
> > + }
> > + (if (!overflow_p)
> > + (div @0 { wide_int_to_tree (type, mul); }))
> > + (if (overflow_p)
> > + { build_zero_cst (type); }))))
> > +
>
> Can't you have something like:
> INT_MIN / 2 / (INT_MIN / -2) == -1
> where
> 2 * (INT_MIN / -2) overflows?
Hmm, right. It should work if overflow_p && mul != INT_MIN as far
as I can see.
I am testing the following.
Thanks,
Richard.
2014-12-02 Richard Biener <rguent...@suse.de>
* match.pd: When combining divisions exclude the degenerate
case involving INT_MIN from overflow handling.
* gcc.dg/torture/20141202-1.c: New testcase.
Index: gcc/match.pd
===================================================================
--- gcc/match.pd (revision 218260)
+++ gcc/match.pd (working copy)
@@ -140,7 +140,9 @@ (define_operator_list inverted_tcc_compa
}
(if (!overflow_p)
(div @0 { wide_int_to_tree (type, mul); }))
- (if (overflow_p)
+ (if (overflow_p
+ && (TYPE_UNSIGNED (type)
+ || mul != wi::min_value (TYPE_PRECISION (type), SIGNED)))
{ build_zero_cst (type); }))))
/* Optimize A / A to 1.0 if we don't care about
Index: gcc/testsuite/gcc.dg/torture/20141202-1.c
===================================================================
--- gcc/testsuite/gcc.dg/torture/20141202-1.c (revision 0)
+++ gcc/testsuite/gcc.dg/torture/20141202-1.c (working copy)
@@ -0,0 +1,15 @@
+/* { dg-do run } */
+
+extern void abort (void);
+
+int foo (int x)
+{
+ return (x / 2) / ((-__INT_MAX__ - 1) / -2);
+}
+
+int main()
+{
+ if (foo (- __INT_MAX__ - 1) != -1)
+ abort ();
+ return 0;
+}
