On Tue, 16 Dec 2014, Marek Polacek wrote:
> As discussed in the PR, this adds folding of (1 << A) & 1) if in
> a eq/ne comparison. The assembly diff on my x86_64 box is
>
> movq %rsp, %rbp
> .cfi_def_cfa_register 6
> movl %edi, -4(%rbp)
> - movl -4(%rbp), %eax
> - movl $1, %edx
> - movl %eax, %ecx
> - sarl %cl, %edx
> - movl %edx, %eax
> - andl $1, %eax
> - testl %eax, %eax
> - setne %al
> + cmpl $0, -4(%rbp)
> + sete %al
> movzbl %al, %eax
> popq %rbp
> .cfi_def_cfa 7, 8
>
> Since this removes a shift, I was afraid that it could regress ubsan
> sanitization, but luckily that is not the case and the shift diagnostics
> seems to be intact.
>
> It triggers several times during the bootstrap.
>
> Bootstrapped/regtested on x86_64-linux + ppc64-linux, ok for trunk?
>
> 2014-12-16 Marek Polacek <[email protected]>
>
> PR middle-end/64309
> * match.pd: Add ((1 << A) & 1) != 0 -> A == 0 and
> ((1 << A) & 1) == 0 -> A != 0.
>
> * gcc.dg/pr64309.c: New test.
>
> diff --git gcc/match.pd gcc/match.pd
> index 083d65f..47b01eb 100644
> --- gcc/match.pd
> +++ gcc/match.pd
> @@ -599,6 +599,15 @@ along with GCC; see the file COPYING3. If not see
> build_int_cst (TREE_TYPE (@1),
> element_precision (type)), @1); }))
>
> +/* ((1 << A) & 1) != 0 -> A == 0 */
> +(simplify
> + (ne (bit_and (lshift integer_onep @0) integer_onep) integer_zerop)
> + (eq @0 { build_zero_cst (TREE_TYPE (@0)); }))
> +
> +/* ((1 << A) & 1) == 0 -> A != 0 */
> +(simplify
> + (eq (bit_and (lshift integer_onep @0) integer_onep) integer_zerop)
> + (ne @0 { build_zero_cst (TREE_TYPE (@0)); }))
You can use
(for cmp (ne eq)
icmp (eq ne)
(simplify
(cmp (bit_and (lshift integer_onep @0) integer_onep) integer_zerop)
(icmp @0 { build_zero_cst (TREE_TYPE (@0)); })))
to combine both patterns. Btw, shoudln't it be (bit_and (...)
integer_each_onep)? I'm always unsure about the complex integer case
(maybe try a runtime testcase and see what happens - eventually we
just don't support bit operations on them...)
Thanks,
Richard.
> /* Simplifications of conversions. */
>
> diff --git gcc/testsuite/gcc.dg/pr64309.c gcc/testsuite/gcc.dg/pr64309.c
> index e69de29..710a762 100644
> --- gcc/testsuite/gcc.dg/pr64309.c
> +++ gcc/testsuite/gcc.dg/pr64309.c
> @@ -0,0 +1,66 @@
> +/* PR middle-end/64309 */
> +/* { dg-do run } */
> +/* { dg-options "-fdump-tree-original" } */
> +
> +int
> +fn1 (int n)
> +{
> + return ((1 << n) & 1) != 0;
> +}
> +
> +int
> +fn2 (int n)
> +{
> + return (1 & (1 << n)) != 0;
> +}
> +
> +int
> +fn3 (int n)
> +{
> + return ((1 << n) & 1) == 0;
> +}
> +
> +int
> +fn4 (int n)
> +{
> + return (1 & (1 << n)) == 0;
> +}
> +
> +int
> +main (void)
> +{
> + if (fn1 (0) != 1
> + || fn1 (1) != 0
> + || fn1 (2) != 0
> + || fn1 (3) != 0
> + || fn1 (4) != 0
> + || fn1 (5) != 0)
> + __builtin_abort ();
> +
> + if (fn2 (0) != 1
> + || fn2 (1) != 0
> + || fn2 (2) != 0
> + || fn2 (3) != 0
> + || fn2 (4) != 0
> + || fn2 (5) != 0)
> + __builtin_abort ();
> +
> + if (fn3 (0) != 0
> + || fn3 (1) != 1
> + || fn3 (2) != 1
> + || fn3 (3) != 1
> + || fn3 (4) != 1
> + || fn3 (5) != 1)
> + __builtin_abort ();
> +
> + if (fn4 (0) != 0
> + || fn4 (1) != 1
> + || fn4 (2) != 1
> + || fn4 (3) != 1
> + || fn4 (4) != 1
> + || fn4 (5) != 1)
> + __builtin_abort ();
> +}
> +
> +/* { dg-final { scan-tree-dump-not "(<<|>>)" "original" } } */
> +/* { dg-final { cleanup-tree-dump "original" } } */
>
> Marek
>
>
--
Richard Biener <[email protected]>
SUSE LINUX GmbH, GF: Felix Imendoerffer, Jane Smithard, Jennifer Guild,
Dilip Upmanyu, Graham Norton HRB 21284 (AG Nuernberg)
