From 90b76a0842b7f080893dd70a7c0c6bc878f4056b Mon Sep 17 00:00:00 2001 From: Michael Schmidt Date: Tue, 5 Dec 2017 14:48:18 +0100 Subject: 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. --- x86/ConstpropOpproof.v | 8 ++++++++ 1 file changed, 8 insertions(+) (limited to 'x86/ConstpropOpproof.v') 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. -- cgit