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) == 0, they can always directly be simplified to 0.
> For example code like:
> unsigned foo(unsigned x)
> {
> unsigned t = (x & 0x00000fff);
> return (t >> 12) & t;
> }
>
> is now simplified into:
> foo:
> ret.32 $0
>
> while previously it was:
> foo:
> and.32 %r2 <- %arg1, $0xfff
> lsr.32 %r4 <- %r2, $12
> and.32 %r6 <- %r4, %r2
> ret.32 %r6
>
> Signed-off-by: Luc Van Oostenryck <luc.vanoostenryck@xxxxxxxxx>
> ---
> simplify.c | 6 +++++-
> validation/optim/lsr-and0.c | 1 -
> 2 files changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/simplify.c b/simplify.c
> index c18965bfa..fe264417e 100644
> --- a/simplify.c
> +++ b/simplify.c
> @@ -590,7 +590,7 @@ static int simplify_or_lsr(struct instruction *insn, pseudo_t src, pseudo_t othe
> static int simplify_shift(struct instruction *insn, pseudo_t pseudo, long long value)
> {
> struct instruction *def;
> - unsigned long long mask, omask;
> + unsigned long long mask, omask, nmask;
> unsigned long long nval;
> unsigned int size;
> pseudo_t src2;
> @@ -649,7 +649,11 @@ static int simplify_shift(struct instruction *insn, pseudo_t pseudo, long long v
> // by (A >> S) & (M >> S)
> if (!constant(def->src2))
> break;
> + mask = bits_mask(insn->size - value) << value;
> omask = def->src2->value;
> + nmask = omask & mask;
> + if (nmask == 0)
> + return replace_with_pseudo(insn, value_pseudo(0));
> if (nbr_users(pseudo) > 1)
> break;
> def->opcode = OP_LSR;
> diff --git a/validation/optim/lsr-and0.c b/validation/optim/lsr-and0.c
> index 292c0332f..94310ba8a 100644
> --- a/validation/optim/lsr-and0.c
> +++ b/validation/optim/lsr-and0.c
> @@ -7,7 +7,6 @@ unsigned lsr_and0(unsigned x)
> /*
> * check-name: lsr-and0
> * check-command: test-linearize -Wno-decl $file
> - * check-known-to-fail
> *
> * check-output-ignore
> * check-output-contains: ret\\..*\\$0$
>
