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Fix PR15346

Message ID alpine.LSU.2.11.1412021003390.5894@zhemvz.fhfr.qr
State New
Headers show

Commit Message

Richard Biener Dec. 2, 2014, 9:21 a.m. UTC 
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  <rguenther@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  <rguenther@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.
diff mbox

Patch

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;
+}