Fix A < 0 ? C : 0 optimization (PR tree-optimization/78720)

On Sat, Dec 10, 2016 at 11:45:35AM +0100, Marc Glisse wrote:
> On Sat, 10 Dec 2016, Jakub Jelinek wrote:
> 
> >	* match.pd (A < 0 ? C : 0): Only optimize for signed A.  If shift
> >	is negative, first convert to @1's type and then lshift it by -shift.
> 
> Thanks, the ChangeLog needs updating.

Indeed, here it is with updated ChangeLog and as an added benefit, also
successfully bootstrapped/regtested on x86_64-linux and i686-linux.

> It is funny to notice that the fact that @1 is a power of 2 has become
> mostly irrelevant. When C fits in the type of A, we can do an arithmetic
> shift right of precision-1 to obtain a mask of 0 or -1, then bit_and works
> not just for powers of 2. Otherwise, imagining that A is int32_t and C
> int64_t, all we care about is that the low 31 bits of C are 0 (otherwise we
> could also do an arithmetic right shift, either before or after the
> convert). But that's another patch, fixing the PR is what matters for now.

You're right.

2016-12-09  Jakub Jelinek  <jakub@redhat.com>
	    Marc Glisse  <marc.glisse@inria.fr>

	PR tree-optimization/78720
	* match.pd (A < 0 ? C : 0): Only optimize for signed A.  If shift
	is negative, sign extend to @1's type and than AND with C.

	* gcc.c-torture/execute/pr78720.c: New test.



	Jakub

On December 10, 2016 12:01:37 PM GMT+01:00, Jakub Jelinek <jakub@redhat.com> wrote:
>On Sat, Dec 10, 2016 at 11:45:35AM +0100, Marc Glisse wrote:
>> On Sat, 10 Dec 2016, Jakub Jelinek wrote:
>> 
>> >	* match.pd (A < 0 ? C : 0): Only optimize for signed A.  If shift
>> >	is negative, first convert to @1's type and then lshift it by
>-shift.
>> 
>> Thanks, the ChangeLog needs updating.
>
>Indeed, here it is with updated ChangeLog and as an added benefit, also
>successfully bootstrapped/regtested on x86_64-linux and i686-linux.

OK.

Richard.

>> It is funny to notice that the fact that @1 is a power of 2 has
>become
>> mostly irrelevant. When C fits in the type of A, we can do an
>arithmetic
>> shift right of precision-1 to obtain a mask of 0 or -1, then bit_and
>works
>> not just for powers of 2. Otherwise, imagining that A is int32_t and
>C
>> int64_t, all we care about is that the low 31 bits of C are 0
>(otherwise we
>> could also do an arithmetic right shift, either before or after the
>> convert). But that's another patch, fixing the PR is what matters for
>now.
>
>You're right.
>
>2016-12-09  Jakub Jelinek  <jakub@redhat.com>
>	    Marc Glisse  <marc.glisse@inria.fr>
>
>	PR tree-optimization/78720
>	* match.pd (A < 0 ? C : 0): Only optimize for signed A.  If shift
>	is negative, sign extend to @1's type and than AND with C.
>
>	* gcc.c-torture/execute/pr78720.c: New test.
>
>--- gcc/match.pd.jj	2016-12-09 10:19:10.909735559 +0100
>+++ gcc/match.pd	2016-12-10 09:21:26.260516596 +0100
>@@ -2768,17 +2768,22 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
>     (ncmp (convert:stype @0) { build_zero_cst (stype); })))))
> 
> /* If we have A < 0 ? C : 0 where C is a power of 2, convert
>-   this into a right shift followed by ANDing with C.  */
>+   this into a right shift or sign extension followed by ANDing with
>C.  */
> (simplify
>  (cond
>   (lt @0 integer_zerop)
>   integer_pow2p@1 integer_zerop)
>- (with {
>+ (if (!TYPE_UNSIGNED (TREE_TYPE (@0)))
>+  (with {
>     int shift = element_precision (@0) - wi::exact_log2 (@1) - 1;
>-  }
>-  (bit_and
>-   (convert (rshift @0 { build_int_cst (integer_type_node, shift); }))
>-   @1)))
>+   }
>+   (if (shift >= 0)
>+    (bit_and
>+     (convert (rshift @0 { build_int_cst (integer_type_node, shift);
>}))
>+     @1)
>+    /* Otherwise ctype must be wider than TREE_TYPE (@0) and pure
>+       sign extension followed by AND with C will achieve the effect. 
>*/
>+    (bit_and (convert @0) @1)))))
> 
>/* When the addresses are not directly of decls compare base and
>offset.
>    This implements some remaining parts of fold_comparison address
>--- gcc/testsuite/gcc.c-torture/execute/pr78720.c.jj	2016-12-10
>09:18:43.386574179 +0100
>+++ gcc/testsuite/gcc.c-torture/execute/pr78720.c	2016-12-10
>09:18:43.386574179 +0100
>@@ -0,0 +1,29 @@
>+/* PR tree-optimization/78720 */
>+
>+__attribute__((noinline, noclone)) long int
>+foo (signed char x)
>+{
>+  return x < 0 ? 0x80000L : 0L;
>+}
>+
>+__attribute__((noinline, noclone)) long int
>+bar (signed char x)
>+{
>+  return x < 0 ? 0x80L : 0L;
>+}
>+
>+__attribute__((noinline, noclone)) long int
>+baz (signed char x)
>+{
>+  return x < 0 ? 0x20L : 0L;
>+}
>+
>+int
>+main ()
>+{
>+  if (foo (-1) != 0x80000L || bar (-1) != 0x80L || baz (-1) != 0x20L
>+      || foo (0) != 0L || bar (0) != 0L || baz (0) != 0L
>+      || foo (31) != 0L || bar (31) != 0L || baz (31) != 0L)
>+    __builtin_abort ();
>+  return 0;
>+}
>
>
>	Jakub