On Mon, 22 Jun 2015, Marek Polacek wrote:
> On Fri, Jun 19, 2015 at 05:51:53PM +0200, Marc Glisse wrote:
> > On Fri, 19 Jun 2015, Marek Polacek wrote:
> >
> > >+/* x + y - (x | y) -> x & y */
> > >+(simplify
> > >+ (minus (plus @0 @1) (bit_ior @0 @1))
> > >+ (if (!TYPE_OVERFLOW_SANITIZED (type) && !TYPE_SATURATING (type))
> > >+ (bit_and @0 @1)))
> > >+
> > >+/* (x + y) - (x & y) -> x | y */
> > >+(simplify
> > >+ (minus (plus @0 @1) (bit_and @0 @1))
> > >+ (if (!TYPE_OVERFLOW_SANITIZED (type) && !TYPE_SATURATING (type))
> > >+ (bit_ior @0 @1)))
> >
> > It could be macroized so they are handled by the same piece of code, but
> > that's not important for a couple lines.
>
> Yeah, that could be done, but I didn't see much value in doing that.
>
> > As far as I can tell, TYPE_SATURATING is for fixed point numbers only, are
> > we allowed to use bit_ior/bit_and on those? I never know what kind of
> > integers are supposed to be supported, so I would have checked
> > TYPE_OVERFLOW_UNDEFINED (type) || TYPE_OVERFLOW_WRAPS (type) since those are
> > the 2 cases where we know it is safe (for TYPE_OVERFLOW_TRAPS it is never
> > clear if we are supposed to preserve traps or just avoid introducing new
> > ones). Well, the reviewer will know, I'll shut up :-)
>
> I think you're right about TYPE_SATURATING so I've dropped that and instead
> replaced it with TYPE_OVERFLOW_TRAPS. That should do the right thing
> together with TYPE_OVERFLOW_SANITIZED.
Are you sure? The point is that if the minus or the plus in the original
expression saturate the result isn't correct, no?
> > (I still believe that the necessity for TYPE_OVERFLOW_SANITIZED here points
> > to a design issue in ubsan, but it is way too late to discuss that)
>
> I think delayed folding would help here a bit. Also, we've been talking
> about doing the signed overflow sanitization earlier, but so far I didn't
> implement that. And -ftrapv should be merged into the ubsan infrastructure
> some day.
>
> > It is probably not worth the trouble adding the variant:
> > x+(y-(x&y)) -> x|y
> > since it decomposes as
> > y-(x&y) -> y&~x
> > x+(y&~x) -> x|y
> > x+(y-(x|y)) -> x-(x&~y) -> x&y is less likely to happen because the first
> > transform y-(x|y) -> -(x&~y) increases the number of insns. Bah, we can't
> > handle everything...
>
> That sounds about right ;). Thanks!
>
> So, Richi, is this variant ok as well? I also added one ubsan test.
As said, removing TYPE_SATURATING doesn't sound correct. I'm not sure
about TYPE_OVERFLOW_TRAPS - we're certainly removing traps elsewhere
(look for the scarce use of this flag in fold-const.c and match.pd
where I only preserved those that were originally in fold-const.c).
So, TYPE_OVERFLOW_TRAPS is your choice but TYPE_SATURATING is
required IMHO.
Richard.
> Bootstrapped/regtested on x86_64-linux, ok for trunk?
>
> 2015-06-22 Marek Polacek <pola...@redhat.com>
>
> * match.pd ((x + y) - (x | y) -> x & y,
> (x + y) - (x & y) -> x | y): New patterns.
>
> * gcc.dg/fold-minus-4.c: New test.
> * gcc.dg/fold-minus-5.c: New test.
> * c-c++-common/ubsan/overflow-add-5.c: New test.
>
> diff --git gcc/match.pd gcc/match.pd
> index badb80a..6d520ef 100644
> --- gcc/match.pd
> +++ gcc/match.pd
> @@ -343,6 +343,18 @@ along with GCC; see the file COPYING3. If not see
> (plus:c (bit_and @0 @1) (bit_ior @0 @1))
> (plus @0 @1))
>
> +/* (x + y) - (x | y) -> x & y */
> +(simplify
> + (minus (plus @0 @1) (bit_ior @0 @1))
> + (if (!TYPE_OVERFLOW_SANITIZED (type) && !TYPE_OVERFLOW_TRAPS (type))
> + (bit_and @0 @1)))
> +
> +/* (x + y) - (x & y) -> x | y */
> +(simplify
> + (minus (plus @0 @1) (bit_and @0 @1))
> + (if (!TYPE_OVERFLOW_SANITIZED (type) && !TYPE_OVERFLOW_TRAPS (type))
> + (bit_ior @0 @1)))
> +
> /* (x | y) - (x ^ y) -> x & y */
> (simplify
> (minus (bit_ior @0 @1) (bit_xor @0 @1))
> diff --git gcc/testsuite/c-c++-common/ubsan/overflow-add-5.c
> gcc/testsuite/c-c++-common/ubsan/overflow-add-5.c
> index e69de29..905a60a 100644
> --- gcc/testsuite/c-c++-common/ubsan/overflow-add-5.c
> +++ gcc/testsuite/c-c++-common/ubsan/overflow-add-5.c
> @@ -0,0 +1,30 @@
> +/* { dg-do run } */
> +/* { dg-options "-fsanitize=signed-integer-overflow" } */
> +
> +int __attribute__ ((noinline))
> +foo (int i, int j)
> +{
> + return (i + j) - (i | j);
> +}
> +
> +/* { dg-output "signed integer overflow: 2147483647 \\+ 1 cannot be
> represented in type 'int'\[^\n\r]*(\n|\r\n|\r)" } */
> +/* { dg-output "\[^\n\r]*signed integer overflow: -2147483648 - 2147483647
> cannot be represented in type 'int'\[^\n\r]*(\n|\r\n|\r)" } */
> +
> +int __attribute__ ((noinline))
> +bar (int i, int j)
> +{
> + return (i + j) - (i & j);
> +}
> +
> +/* { dg-output "\[^\n\r]*signed integer overflow: 2147483647 \\+ 1 cannot be
> represented in type 'int'\[^\n\r]*(\n|\r\n|\r)" } */
> +/* { dg-output "\[^\n\r]*signed integer overflow: -2147483648 - 1 cannot be
> represented in type 'int'" } */
> +
> +int
> +main ()
> +{
> + int r = foo (__INT_MAX__, 1);
> + asm volatile ("" : "+g" (r));
> + r = bar (__INT_MAX__, 1);
> + asm volatile ("" : "+g" (r));
> + return 0;
> +}
> diff --git gcc/testsuite/gcc.dg/fold-minus-4.c
> gcc/testsuite/gcc.dg/fold-minus-4.c
> index e69de29..2d76b4f 100644
> --- gcc/testsuite/gcc.dg/fold-minus-4.c
> +++ gcc/testsuite/gcc.dg/fold-minus-4.c
> @@ -0,0 +1,37 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O -fdump-tree-cddce1" } */
> +
> +int
> +fn1 (int a, int b)
> +{
> + int tem1 = a + b;
> + int tem2 = a & b;
> + return tem1 - tem2;
> +}
> +
> +int
> +fn2 (int a, int b)
> +{
> + int tem1 = b + a;
> + int tem2 = a & b;
> + return tem1 - tem2;
> +}
> +
> +int
> +fn3 (int a, int b)
> +{
> + int tem1 = a + b;
> + int tem2 = b & a;
> + return tem1 - tem2;
> +}
> +
> +int
> +fn4 (int a, int b)
> +{
> + int tem1 = b + a;
> + int tem2 = b & a;
> + return tem1 - tem2;
> +}
> +
> +/* { dg-final { scan-tree-dump-not " & " "cddce1" } } */
> +/* { dg-final { scan-tree-dump-not " \\+ " "cddce1" } } */
> diff --git gcc/testsuite/gcc.dg/fold-minus-5.c
> gcc/testsuite/gcc.dg/fold-minus-5.c
> index e69de29..a31e1cc 100644
> --- gcc/testsuite/gcc.dg/fold-minus-5.c
> +++ gcc/testsuite/gcc.dg/fold-minus-5.c
> @@ -0,0 +1,37 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O -fdump-tree-cddce1" } */
> +
> +int
> +fn1 (int a, int b)
> +{
> + int tem1 = a + b;
> + int tem2 = a | b;
> + return tem1 - tem2;
> +}
> +
> +int
> +fn2 (int a, int b)
> +{
> + int tem1 = b + a;
> + int tem2 = a | b;
> + return tem1 - tem2;
> +}
> +
> +int
> +fn3 (int a, int b)
> +{
> + int tem1 = a + b;
> + int tem2 = b | a;
> + return tem1 - tem2;
> +}
> +
> +int
> +fn4 (int a, int b)
> +{
> + int tem1 = b + a;
> + int tem2 = b | a;
> + return tem1 - tem2;
> +}
> +
> +/* { dg-final { scan-tree-dump-not " \\+ " "cddce1" } } */
> +/* { dg-final { scan-tree-dump-not " \\| " "cddce1" } } */
>
> Marek
>
>
--
Richard Biener <rguent...@suse.de>
SUSE LINUX GmbH, GF: Felix Imendoerffer, Jane Smithard, Dilip Upmanyu, Graham
Norton, HRB 21284 (AG Nuernberg)
