On 19/08/18 10:29, Luc Van Oostenryck wrote:
> The instructions LSR(AND(x, M), S) are already simplified into
> AND(LSR(x, S), (M >> 12)) but only if AND(x, M) has a single user.
s/(M >> 12)/(M >> S)/
ATB,
Ramsay Jones
>
> However, if (M >> S) == (-1 >> S), the AND part is redundant and the
> whole can always directly be simplified into LSR(x, S).
>
> For example, code like:
> unsigned foo(unsigned x)
> {
> unsigned t = (x & 0xfffff000);
> return ((t >> 12) ^ (x >> 12)) & t;
> }
>
> is now optimized into:
> foo:
> ret.32 $0
>
> because (t >> 12) is simplified into (x >> 12).
>
> Signed-off-by: Luc Van Oostenryck <luc.vanoostenryck@xxxxxxxxx>
> ---
> simplify.c | 2 ++
> validation/optim/lsr-and1.c | 1 -
> 2 files changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/simplify.c b/simplify.c
> index fe264417e..8ace8a5da 100644
> --- a/simplify.c
> +++ b/simplify.c
> @@ -654,6 +654,8 @@ static int simplify_shift(struct instruction *insn, pseudo_t pseudo, long long v
> nmask = omask & mask;
> if (nmask == 0)
> return replace_with_pseudo(insn, value_pseudo(0));
> + if (nmask == mask)
> + return replace_pseudo(insn, &insn->src1, def->src1);
> if (nbr_users(pseudo) > 1)
> break;
> def->opcode = OP_LSR;
> diff --git a/validation/optim/lsr-and1.c b/validation/optim/lsr-and1.c
> index 906d9946f..ad249848b 100644
> --- a/validation/optim/lsr-and1.c
> +++ b/validation/optim/lsr-and1.c
> @@ -11,7 +11,6 @@ unsigned foo(unsigned x)
> /*
> * check-name: lsr-and1
> * check-command: test-linearize -Wno-decl $file
> - * check-known-to-fail
> *
> * check-output-ignore
> * check-output-contains: ret\\..*\\$0$
>
