| Message ID | 20170809193806.30975-8-luc.vanoostenryck@gmail.com (mailing list archive) |
|---|---|
| State | Superseded, archived |
| Headers | show |
On Wed, Aug 9, 2017 at 3:38 PM, Luc Van Oostenryck <luc.vanoostenryck@gmail.com> wrote: > This is especially usefull when simplifying code > accessing bitfields. > > Signed-off-by: Luc Van Oostenryck <luc.vanoostenryck@gmail.com> > --- > simplify.c | 29 ++++++++++++++++++++++++++++- > validation/bitfield-size.c | 4 +--- > 2 files changed, 29 insertions(+), 4 deletions(-) > > diff --git a/simplify.c b/simplify.c > index 40d4f0068..e8bf1c171 100644 > --- a/simplify.c > +++ b/simplify.c > @@ -411,6 +411,32 @@ static int simplify_asr(struct instruction *insn, pseudo_t pseudo, long long val > return 0; > } > > +static int simplify_lsr(struct instruction *insn, pseudo_t pseudo, long long value) > +{ > + struct instruction *def; > + unsigned long long mask; > + > + if (!value) > + return replace_with_pseudo(insn, pseudo); > + switch (def_opcode(insn->src1)) { > + case OP_AND: > + // replace (A & M) >> S > + // by (A >> S) & (M >> S) A little bit suggestion base on my previous reading and question ask on this. When I first read the comment without reading the code, then I would wondering why (A>>S) & (M>>S) is simpler. The following code actually explain the constant mask very well. So the comment best understand if the code was read. Adding some comment on M is constant will help a lot in the comment. Not a reason to object the patch of course. Just suggestions. Chris -- To unsubscribe from this list: send the line "unsubscribe linux-sparse" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Thu, Aug 10, 2017 at 3:16 AM, Christopher Li <sparse@chrisli.org> wrote: >> + // replace (A & M) >> S >> + // by (A >> S) & (M >> S) > > A little bit suggestion base on my previous reading and question ask on > this. When I first read the comment without reading the code, then I would > wondering why (A>>S) & (M>>S) is simpler. The following code actually > explain the constant mask very well. So the comment best understand if > the code was read. Adding some comment on M is constant will help a > lot in the comment. Yes. In fact, these patches still need to have a proper commit message. I've added a not for now. --Luc -- To unsubscribe from this list: send the line "unsubscribe linux-sparse" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/simplify.c b/simplify.c index 40d4f0068..e8bf1c171 100644 --- a/simplify.c +++ b/simplify.c @@ -411,6 +411,32 @@ static int simplify_asr(struct instruction *insn, pseudo_t pseudo, long long val return 0; } +static int simplify_lsr(struct instruction *insn, pseudo_t pseudo, long long value) +{ + struct instruction *def; + unsigned long long mask; + + if (!value) + return replace_with_pseudo(insn, pseudo); + switch (def_opcode(insn->src1)) { + case OP_AND: + // replace (A & M) >> S + // by (A >> S) & (M >> S) + def = insn->src1->def; + if (!constant(def->src2)) + break; + if (nbr_pseudo_users(insn->src1) > 1) + break; + mask = def->src2->value; + def->opcode = OP_LSR; + def->src2 = value_pseudo(value); + insn->opcode = OP_AND; + insn->src2 = value_pseudo(mask >> value); + return REPEAT_CSE; + } + return 0; +} + static int simplify_mul_div(struct instruction *insn, long long value) { unsigned long long sbit = 1ULL << (insn->size - 1); @@ -561,13 +587,14 @@ static int simplify_constant_rightside(struct instruction *insn) case OP_ADD: case OP_OR: case OP_XOR: case OP_SHL: - case OP_LSR: case_neutral_zero: if (!value) return replace_with_pseudo(insn, insn->src1); return 0; case OP_ASR: return simplify_asr(insn, insn->src1, value); + case OP_LSR: + return simplify_lsr(insn, insn->src1, value); case OP_MODU: case OP_MODS: if (value == 1) diff --git a/validation/bitfield-size.c b/validation/bitfield-size.c index c8c94bb15..34400479a 100644 --- a/validation/bitfield-size.c +++ b/validation/bitfield-size.c @@ -36,8 +36,6 @@ unsigned int get_pbfi_b(struct bfi *bf) { return bf->b; } * check-output-ignore * * check-output-excludes: cast\\.4 - * check-output-pattern-6-times: cast\\. * check-output-pattern-6-times: lsr\\..*\\$6 - * check-output-pattern-6-times: and\\..*\\$15 - * check-output-pattern-6-times: and\\..*\\$960 + * check-output-pattern-12-times: and\\..*\\$15 */
This is especially usefull when simplifying code accessing bitfields. Signed-off-by: Luc Van Oostenryck <luc.vanoostenryck@gmail.com> --- simplify.c | 29 ++++++++++++++++++++++++++++- validation/bitfield-size.c | 4 +--- 2 files changed, 29 insertions(+), 4 deletions(-)