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Re: [PATCH] Fix wrong-code when folding X - (X / Y) * Y (PR tree-optimization/67953)
- From: Richard Biener <rguenther at suse dot de>
- To: Marek Polacek <polacek at redhat dot com>,GCC Patches <gcc-patches at gcc dot gnu dot org>,Marc Glisse <marc dot glisse at inria dot fr>
- Date: Wed, 14 Oct 2015 20:44:55 +0200
- Subject: Re: [PATCH] Fix wrong-code when folding X - (X / Y) * Y (PR tree-optimization/67953)
- Authentication-results: sourceware.org; auth=none
- References: <20151014182731 dot GJ13672 at redhat dot com>
On October 14, 2015 8:27:31 PM GMT+02:00, Marek Polacek <polacek@redhat.com> wrote:
>Evidently, the X - (X / Y) * Y -> X % Y pattern can't change the
>signedness of X from signed to unsigned, otherwise we'd generate
>wrong code. (But unsigned -> signed should be fine.)
>
>Does anyone see a better fix than this?
>
>Bootstrapped/regtested on x86_64-linux, ok for trunk?
OK.
Thanks,
Richard.
>2015-10-14 Marek Polacek <polacek@redhat.com>
>
> PR tree-optimization/67953
> * match.pd (X - (X / Y) * Y): Don't change signedness of @0.
>
> * gcc.dg/fold-minus-6.c (fn4): Change the type of A to
> unsigned.
> * gcc.dg/torture/pr67953.c: New test.
>
>diff --git gcc/match.pd gcc/match.pd
>index 655c9ff..24e19a9 100644
>--- gcc/match.pd
>+++ gcc/match.pd
>@@ -267,7 +267,8 @@ along with GCC; see the file COPYING3. If not see
> /* X - (X / Y) * Y is the same as X % Y. */
> (simplify
> (minus (convert1? @0) (convert2? (mult (trunc_div @0 @1) @1)))
>- (if (INTEGRAL_TYPE_P (type) || VECTOR_INTEGER_TYPE_P (type))
>+ (if ((INTEGRAL_TYPE_P (type) || VECTOR_INTEGER_TYPE_P (type))
>+ && TYPE_UNSIGNED (TREE_TYPE (@0)) == TYPE_UNSIGNED (type))
> (trunc_mod (convert @0) (convert @1))))
>
> /* Optimize TRUNC_MOD_EXPR by a power of two into a BIT_AND_EXPR,
>diff --git gcc/testsuite/gcc.dg/fold-minus-6.c
>gcc/testsuite/gcc.dg/fold-minus-6.c
>index 1c22c25..1535452 100644
>--- gcc/testsuite/gcc.dg/fold-minus-6.c
>+++ gcc/testsuite/gcc.dg/fold-minus-6.c
>@@ -20,7 +20,7 @@ fn3 (long int x)
> }
>
> int
>-fn4 (int a, int b)
>+fn4 (unsigned int a, int b)
> {
> return a - (unsigned) ((a / b) * b);
> }
>diff --git gcc/testsuite/gcc.dg/torture/pr67953.c
>gcc/testsuite/gcc.dg/torture/pr67953.c
>index e69de29..5ce399b 100644
>--- gcc/testsuite/gcc.dg/torture/pr67953.c
>+++ gcc/testsuite/gcc.dg/torture/pr67953.c
>@@ -0,0 +1,42 @@
>+/* PR tree-optimization/67953 */
>+/* { dg-do run } */
>+
>+unsigned int
>+fn1 (signed int a)
>+{
>+ return (unsigned int) a - ((a / 3) * 3);
>+}
>+
>+unsigned int
>+fn2 (signed int a)
>+{
>+ return a - ((a / 3) * 3);
>+}
>+
>+unsigned int
>+fn3 (int a)
>+{
>+ return a - (unsigned) ((a / 3) * 3);
>+}
>+
>+signed int
>+fn4 (int a)
>+{
>+ return (unsigned) a - (unsigned) ((a / 3) * 3);
>+}
>+
>+signed int
>+fn5 (unsigned int a)
>+{
>+ return (signed) a - (int) ((a / 3) * 3);
>+}
>+
>+int
>+main ()
>+{
>+ if (fn1 (-5) != -2
>+ || fn2 (-5) != -2
>+ || fn3 (-5) != -2
>+ || fn4 (-5) != -2)
>+ __builtin_abort ();
>+}
>
> Marek