src/HOL/IMP/Abs_Int1.thy

tuned messages

(* Author: Tobias Nipkow *)

theory Abs_Int1
imports Abs_State
begin

subsection "Computable Abstract Interpretation"

text{* Abstract interpretation over type @{text st} instead of functions. *}

context Gamma_semilattice
begin

fun aval' :: "aexp \<Rightarrow> 'av st \<Rightarrow> 'av" where
"aval' (N i) S = num' i" |
"aval' (V x) S = fun S x" |
"aval' (Plus a1 a2) S = plus' (aval' a1 S) (aval' a2 S)"

lemma aval'_correct: "s : \<gamma>\<^sub>s S \<Longrightarrow> aval a s : \<gamma>(aval' a S)"
by (induction a) (auto simp: gamma_num' gamma_plus' \<gamma>_st_def)

lemma gamma_Step_subcomm: fixes C1 C2 :: "'a::semilattice_sup acom"
  assumes "!!x e S. f1 x e (\<gamma>\<^sub>o S) \<subseteq> \<gamma>\<^sub>o (f2 x e S)"
          "!!b S. g1 b (\<gamma>\<^sub>o S) \<subseteq> \<gamma>\<^sub>o (g2 b S)"
  shows "Step f1 g1 (\<gamma>\<^sub>o S) (\<gamma>\<^sub>c C) \<le> \<gamma>\<^sub>c (Step f2 g2 S C)"
proof(induction C arbitrary: S)
qed (auto simp: assms intro!: mono_gamma_o sup_ge1 sup_ge2)

lemma in_gamma_update: "\<lbrakk> s : \<gamma>\<^sub>s S; i : \<gamma> a \<rbrakk> \<Longrightarrow> s(x := i) : \<gamma>\<^sub>s(update S x a)"
by(simp add: \<gamma>_st_def)

end


locale Abs_Int = Gamma_semilattice where \<gamma>=\<gamma>
  for \<gamma> :: "'av::semilattice_sup_top \<Rightarrow> val set"
begin

definition "step' = Step
  (\<lambda>x e S. case S of None \<Rightarrow> None | Some S \<Rightarrow> Some(update S x (aval' e S)))
  (\<lambda>b S. S)"

definition AI :: "com \<Rightarrow> 'av st option acom option" where
"AI c = pfp (step' \<top>) (bot c)"


lemma strip_step'[simp]: "strip(step' S C) = strip C"
by(simp add: step'_def)


text{* Correctness: *}

lemma step_step': "step (\<gamma>\<^sub>o S) (\<gamma>\<^sub>c C) \<le> \<gamma>\<^sub>c (step' S C)"
unfolding step_def step'_def
by(rule gamma_Step_subcomm)
  (auto simp: intro!: aval'_correct in_gamma_update split: option.splits)

lemma AI_correct: "AI c = Some C \<Longrightarrow> CS c \<le> \<gamma>\<^sub>c C"
proof(simp add: CS_def AI_def)
  assume 1: "pfp (step' \<top>) (bot c) = Some C"
  have pfp': "step' \<top> C \<le> C" by(rule pfp_pfp[OF 1])
  have 2: "step (\<gamma>\<^sub>o \<top>) (\<gamma>\<^sub>c C) \<le> \<gamma>\<^sub>c C"  --"transfer the pfp'"
  proof(rule order_trans)
    show "step (\<gamma>\<^sub>o \<top>) (\<gamma>\<^sub>c C) \<le> \<gamma>\<^sub>c (step' \<top> C)" by(rule step_step')
    show "... \<le> \<gamma>\<^sub>c C" by (metis mono_gamma_c[OF pfp'])
  qed
  have 3: "strip (\<gamma>\<^sub>c C) = c" by(simp add: strip_pfp[OF _ 1] step'_def)
  have "lfp c (step (\<gamma>\<^sub>o \<top>)) \<le> \<gamma>\<^sub>c C"
    by(rule lfp_lowerbound[simplified,where f="step (\<gamma>\<^sub>o \<top>)", OF 3 2])
  thus "lfp c (step UNIV) \<le> \<gamma>\<^sub>c C" by simp
qed

end


subsubsection "Monotonicity"

locale Abs_Int_mono = Abs_Int +
assumes mono_plus': "a1 \<le> b1 \<Longrightarrow> a2 \<le> b2 \<Longrightarrow> plus' a1 a2 \<le> plus' b1 b2"
begin

lemma mono_aval': "S1 \<le> S2 \<Longrightarrow> aval' e S1 \<le> aval' e S2"
by(induction e) (auto simp: mono_plus' mono_fun)

theorem mono_step': "S1 \<le> S2 \<Longrightarrow> C1 \<le> C2 \<Longrightarrow> step' S1 C1 \<le> step' S2 C2"
unfolding step'_def
by(rule mono2_Step) (auto simp: mono_aval' split: option.split)

lemma mono_step'_top: "C \<le> C' \<Longrightarrow> step' \<top> C \<le> step' \<top> C'"
by (metis mono_step' order_refl)

lemma AI_least_pfp: assumes "AI c = Some C" "step' \<top> C' \<le> C'" "strip C' = c"
shows "C \<le> C'"
by(rule pfp_bot_least[OF _ _ assms(2,3) assms(1)[unfolded AI_def]])
  (simp_all add: mono_step'_top)

end


subsubsection "Termination"

locale Measure1 =
fixes m :: "'av::order_top \<Rightarrow> nat"
fixes h :: "nat"
assumes h: "m x \<le> h"
begin

definition m_s :: "'av st \<Rightarrow> vname set \<Rightarrow> nat" ("m\<^sub>s") where
"m_s S X = (\<Sum> x \<in> X. m(fun S x))"

lemma m_s_h: "finite X \<Longrightarrow> m_s S X \<le> h * card X"
by(simp add: m_s_def) (metis mult.commute of_nat_id setsum_bounded[OF h])

definition m_o :: "'av st option \<Rightarrow> vname set \<Rightarrow> nat" ("m\<^sub>o") where
"m_o opt X = (case opt of None \<Rightarrow> h * card X + 1 | Some S \<Rightarrow> m_s S X)"

lemma m_o_h: "finite X \<Longrightarrow> m_o opt X \<le> (h*card X + 1)"
by(auto simp add: m_o_def m_s_h le_SucI split: option.split dest:m_s_h)

definition m_c :: "'av st option acom \<Rightarrow> nat" ("m\<^sub>c") where
"m_c C = listsum (map (\<lambda>a. m_o a (vars C)) (annos C))"

text{* Upper complexity bound: *}
lemma m_c_h: "m_c C \<le> size(annos C) * (h * card(vars C) + 1)"
proof-
  let ?X = "vars C" let ?n = "card ?X" let ?a = "size(annos C)"
  have "m_c C = (\<Sum>i<?a. m_o (annos C ! i) ?X)"
    by(simp add: m_c_def listsum_setsum_nth atLeast0LessThan)
  also have "\<dots> \<le> (\<Sum>i<?a. h * ?n + 1)"
    apply(rule setsum_mono) using m_o_h[OF finite_Cvars] by simp
  also have "\<dots> = ?a * (h * ?n + 1)" by simp
  finally show ?thesis .
qed

end

fun top_on_st :: "'a::order_top st \<Rightarrow> vname set \<Rightarrow> bool" ("top'_on\<^sub>s") where
"top_on_st S X = (\<forall>x\<in>X. fun S x = \<top>)"

fun top_on_opt :: "'a::order_top st option \<Rightarrow> vname set \<Rightarrow> bool" ("top'_on\<^sub>o") where
"top_on_opt (Some S)  X = top_on_st S X" |
"top_on_opt None X = True"

definition top_on_acom :: "'a::order_top st option acom \<Rightarrow> vname set \<Rightarrow> bool" ("top'_on\<^sub>c") where
"top_on_acom C X = (\<forall>a \<in> set(annos C). top_on_opt a X)"

lemma top_on_top: "top_on_opt (\<top>::_ st option) X"
by(auto simp: top_option_def fun_top)

lemma top_on_bot: "top_on_acom (bot c) X"
by(auto simp add: top_on_acom_def bot_def)

lemma top_on_post: "top_on_acom C X \<Longrightarrow> top_on_opt (post C) X"
by(simp add: top_on_acom_def post_in_annos)

lemma top_on_acom_simps:
  "top_on_acom (SKIP {Q}) X = top_on_opt Q X"
  "top_on_acom (x ::= e {Q}) X = top_on_opt Q X"
  "top_on_acom (C1;;C2) X = (top_on_acom C1 X \<and> top_on_acom C2 X)"
  "top_on_acom (IF b THEN {P1} C1 ELSE {P2} C2 {Q}) X =
   (top_on_opt P1 X \<and> top_on_acom C1 X \<and> top_on_opt P2 X \<and> top_on_acom C2 X \<and> top_on_opt Q X)"
  "top_on_acom ({I} WHILE b DO {P} C {Q}) X =
   (top_on_opt I X \<and> top_on_acom C X \<and> top_on_opt P X \<and> top_on_opt Q X)"
by(auto simp add: top_on_acom_def)

lemma top_on_sup:
  "top_on_opt o1 X \<Longrightarrow> top_on_opt o2 X \<Longrightarrow> top_on_opt (o1 \<squnion> o2 :: _ st option) X"
apply(induction o1 o2 rule: sup_option.induct)
apply(auto)
by transfer simp

lemma top_on_Step: fixes C :: "('a::semilattice_sup_top)st option acom"
assumes "!!x e S. \<lbrakk>top_on_opt S X; x \<notin> X; vars e \<subseteq> -X\<rbrakk> \<Longrightarrow> top_on_opt (f x e S) X"
        "!!b S. top_on_opt S X \<Longrightarrow> vars b \<subseteq> -X \<Longrightarrow> top_on_opt (g b S) X"
shows "\<lbrakk> vars C \<subseteq> -X; top_on_opt S X; top_on_acom C X \<rbrakk> \<Longrightarrow> top_on_acom (Step f g S C) X"
proof(induction C arbitrary: S)
qed (auto simp: top_on_acom_simps vars_acom_def top_on_post top_on_sup assms)


locale Measure = Measure1 +
assumes m2: "x < y \<Longrightarrow> m x > m y"
begin

lemma m1: "x \<le> y \<Longrightarrow> m x \<ge> m y"
by(auto simp: le_less m2)

lemma m_s2_rep: assumes "finite(X)" and "S1 = S2 on -X" and "\<forall>x. S1 x \<le> S2 x" and "S1 \<noteq> S2"
shows "(\<Sum>x\<in>X. m (S2 x)) < (\<Sum>x\<in>X. m (S1 x))"
proof-
  from assms(3) have 1: "\<forall>x\<in>X. m(S1 x) \<ge> m(S2 x)" by (simp add: m1)
  from assms(2,3,4) have "EX x:X. S1 x < S2 x"
    by(simp add: fun_eq_iff) (metis Compl_iff le_neq_trans)
  hence 2: "\<exists>x\<in>X. m(S1 x) > m(S2 x)" by (metis m2)
  from setsum_strict_mono_ex1[OF `finite X` 1 2]
  show "(\<Sum>x\<in>X. m (S2 x)) < (\<Sum>x\<in>X. m (S1 x))" .
qed

lemma m_s2: "finite(X) \<Longrightarrow> fun S1 = fun S2 on -X
  \<Longrightarrow> S1 < S2 \<Longrightarrow> m_s S1 X > m_s S2 X"
apply(auto simp add: less_st_def m_s_def)
apply (transfer fixing: m)
apply(simp add: less_eq_st_rep_iff eq_st_def m_s2_rep)
done

lemma m_o2: "finite X \<Longrightarrow> top_on_opt o1 (-X) \<Longrightarrow> top_on_opt o2 (-X) \<Longrightarrow>
  o1 < o2 \<Longrightarrow> m_o o1 X > m_o o2 X"
proof(induction o1 o2 rule: less_eq_option.induct)
  case 1 thus ?case by (auto simp: m_o_def m_s2 less_option_def)
next
  case 2 thus ?case by(auto simp: m_o_def less_option_def le_imp_less_Suc m_s_h)
next
  case 3 thus ?case by (auto simp: less_option_def)
qed

lemma m_o1: "finite X \<Longrightarrow> top_on_opt o1 (-X) \<Longrightarrow> top_on_opt o2 (-X) \<Longrightarrow>
  o1 \<le> o2 \<Longrightarrow> m_o o1 X \<ge> m_o o2 X"
by(auto simp: le_less m_o2)


lemma m_c2: "top_on_acom C1 (-vars C1) \<Longrightarrow> top_on_acom C2 (-vars C2) \<Longrightarrow>
  C1 < C2 \<Longrightarrow> m_c C1 > m_c C2"
proof(auto simp add: le_iff_le_annos size_annos_same[of C1 C2] vars_acom_def less_acom_def)
  let ?X = "vars(strip C2)"
  assume top: "top_on_acom C1 (- vars(strip C2))"  "top_on_acom C2 (- vars(strip C2))"
  and strip_eq: "strip C1 = strip C2"
  and 0: "\<forall>i<size(annos C2). annos C1 ! i \<le> annos C2 ! i"
  hence 1: "\<forall>i<size(annos C2). m_o (annos C1 ! i) ?X \<ge> m_o (annos C2 ! i) ?X"
    apply (auto simp: all_set_conv_all_nth vars_acom_def top_on_acom_def)
    by (metis finite_cvars m_o1 size_annos_same2)
  fix i assume i: "i < size(annos C2)" "\<not> annos C2 ! i \<le> annos C1 ! i"
  have topo1: "top_on_opt (annos C1 ! i) (- ?X)"
    using i(1) top(1) by(simp add: top_on_acom_def size_annos_same[OF strip_eq])
  have topo2: "top_on_opt (annos C2 ! i) (- ?X)"
    using i(1) top(2) by(simp add: top_on_acom_def size_annos_same[OF strip_eq])
  from i have "m_o (annos C1 ! i) ?X > m_o (annos C2 ! i) ?X" (is "?P i")
    by (metis 0 less_option_def m_o2[OF finite_cvars topo1] topo2)
  hence 2: "\<exists>i < size(annos C2). ?P i" using `i < size(annos C2)` by blast
  have "(\<Sum>i<size(annos C2). m_o (annos C2 ! i) ?X)
         < (\<Sum>i<size(annos C2). m_o (annos C1 ! i) ?X)"
    apply(rule setsum_strict_mono_ex1) using 1 2 by (auto)
  thus ?thesis
    by(simp add: m_c_def vars_acom_def strip_eq listsum_setsum_nth atLeast0LessThan size_annos_same[OF strip_eq])
qed

end


locale Abs_Int_measure =
  Abs_Int_mono where \<gamma>=\<gamma> + Measure where m=m
  for \<gamma> :: "'av::semilattice_sup_top \<Rightarrow> val set" and m :: "'av \<Rightarrow> nat"
begin

lemma top_on_step': "\<lbrakk> top_on_acom C (-vars C) \<rbrakk> \<Longrightarrow> top_on_acom (step' \<top> C) (-vars C)"
unfolding step'_def
by(rule top_on_Step)
  (auto simp add: top_option_def fun_top split: option.splits)

lemma AI_Some_measure: "\<exists>C. AI c = Some C"
unfolding AI_def
apply(rule pfp_termination[where I = "\<lambda>C. top_on_acom C (- vars C)" and m="m_c"])
apply(simp_all add: m_c2 mono_step'_top bot_least top_on_bot)
using top_on_step' apply(auto simp add: vars_acom_def)
done

end

end