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| author | Michael Schmidt <github@mschmidt.me> | 2017-12-05 14:48:18 +0100 |
|---|---|---|
| committer | Xavier Leroy <xavierleroy@users.noreply.github.com> | 2017-12-05 14:48:18 +0100 |
| commit | 90b76a0842b7f080893dd70a7c0c6bc878f4056b (patch) | |
| tree | 277edd1eecf7bc7574a4b4dc3b925e3479dab8fd /x86 | |
| parent | 442e82e6ffc6958192f73382d2270e926ead9c80 (diff) | |
| download | compcert-kvx-90b76a0842b7f080893dd70a7c0c6bc878f4056b.tar.gz compcert-kvx-90b76a0842b7f080893dd70a7c0c6bc878f4056b.zip | |
Optimization for division by one during constant propagation (#39)
Signed and unsigned divisions by literal 1 are already optimized away during the Selection phase. This pull request also optimizes those divisions when the 1 divisor is produced by constant propagation.
Diffstat (limited to 'x86')
| -rw-r--r-- | x86/ConstpropOp.vp | 26 | ||||
| -rw-r--r-- | x86/ConstpropOpproof.v | 8 |
2 files changed, 24 insertions, 10 deletions
diff --git a/x86/ConstpropOp.vp b/x86/ConstpropOp.vp index f0000a85..be0cc09a 100644 --- a/x86/ConstpropOp.vp +++ b/x86/ConstpropOp.vp @@ -248,18 +248,24 @@ Definition make_xorimm (n: int) (r: reg) := else (Oxorimm n, r :: nil). Definition make_divimm n (r1 r2: reg) := - match Int.is_power2 n with - | Some l => if Int.ltu l (Int.repr 31) - then (Oshrximm l, r1 :: nil) - else (Odiv, r1 :: r2 :: nil) - | None => (Odiv, r1 :: r2 :: nil) - end. + if Int.eq n Int.one then + (Omove, r1 :: nil) + else + match Int.is_power2 n with + | Some l => if Int.ltu l (Int.repr 31) + then (Oshrximm l, r1 :: nil) + else (Odiv, r1 :: r2 :: nil) + | None => (Odiv, r1 :: r2 :: nil) + end. Definition make_divuimm n (r1 r2: reg) := - match Int.is_power2 n with - | Some l => (Oshruimm l, r1 :: nil) - | None => (Odivu, r1 :: r2 :: nil) - end. + if Int.eq n Int.one then + (Omove, r1 :: nil) + else + match Int.is_power2 n with + | Some l => (Oshruimm l, r1 :: nil) + | None => (Odivu, r1 :: r2 :: nil) + end. Definition make_moduimm n (r1 r2: reg) := match Int.is_power2 n with diff --git a/x86/ConstpropOpproof.v b/x86/ConstpropOpproof.v index ce20738c..e82c2963 100644 --- a/x86/ConstpropOpproof.v +++ b/x86/ConstpropOpproof.v @@ -421,6 +421,10 @@ Lemma make_divimm_correct: exists w, eval_operation ge (Vptr sp Ptrofs.zero) op e##args m = Some w /\ Val.lessdef v w. Proof. intros; unfold make_divimm. + predSpec Int.eq Int.eq_spec n Int.one; intros. subst. rewrite H0 in H. + destruct (e#r1) eqn:?; + try (rewrite Val.divs_one in H; exists (Vint i); split; simpl; try rewrite Heqv0; auto); + inv H; auto. destruct (Int.is_power2 n) eqn:?. destruct (Int.ltu i (Int.repr 31)) eqn:?. exists v; split; auto. simpl. eapply Val.divs_pow2; eauto. congruence. @@ -436,6 +440,10 @@ Lemma make_divuimm_correct: exists w, eval_operation ge (Vptr sp Ptrofs.zero) op e##args m = Some w /\ Val.lessdef v w. Proof. intros; unfold make_divuimm. + predSpec Int.eq Int.eq_spec n Int.one; intros. subst. rewrite H0 in H. + destruct (e#r1) eqn:?; + try (rewrite Val.divu_one in H; exists (Vint i); split; simpl; try rewrite Heqv0; auto); + inv H; auto. destruct (Int.is_power2 n) eqn:?. econstructor; split. simpl; eauto. rewrite H0 in H. erewrite Val.divu_pow2 by eauto. auto. |