Assorted changes to reduce stack and heap requirements when compiling very big functions.

git-svn-id: https://yquem.inria.fr/compcert/svn/compcert/trunk@2151 fca1b0fc-160b-0410-b1d3-a4f43f01ea2e

2 files changed, 29 insertions, 9 deletions

diff --git a/powerpc/Asmgen.v b/powerpc/Asmgen.v
index 0035dff..39b84e0 100644
--- a/powerpc/Asmgen.v
+++ b/powerpc/Asmgen.v
@@ -621,7 +621,7 @@ Definition transl_instr (f: Mach.function) (i: Mach.instruction)
 
 (** Translation of a code sequence *)
 
-Definition r11_is_parent (before: bool) (i: Mach.instruction) : bool :=
+Definition it1_is_parent (before: bool) (i: Mach.instruction) : bool :=
   match i with
   | Msetstack src ofs ty => before
   | Mgetparam ofs ty dst => negb (mreg_eq dst IT1)
@@ -629,21 +629,39 @@ Definition r11_is_parent (before: bool) (i: Mach.instruction) : bool :=
   | _ => false
   end.
 
-Fixpoint transl_code (f: Mach.function) (il: list Mach.instruction)  (r11p: bool) :=
+(** This is the naive definition that we no longer use because it
+  is not tail-recursive.  It is kept as specification. *)
+
+Fixpoint transl_code (f: Mach.function) (il: list Mach.instruction) (it1p: bool) :=
   match il with
   | nil => OK nil
   | i1 :: il' =>
-      do k <- transl_code f il' (r11_is_parent r11p i1);
-      transl_instr f i1 r11p k
+      do k <- transl_code f il' (it1_is_parent it1p i1);
+      transl_instr f i1 it1p k
   end.
 
+(** This is an equivalent definition in continuation-passing style
+  that runs in constant stack space. *)
+
+Fixpoint transl_code_rec (f: Mach.function) (il: list Mach.instruction)
+                         (it1p: bool) (k: code -> res code) :=
+  match il with
+  | nil => k nil
+  | i1 :: il' =>
+      transl_code_rec f il' (it1_is_parent it1p i1)
+        (fun c1 => do c2 <- transl_instr f i1 it1p c1; k c2)
+  end.
+
+Definition transl_code' (f: Mach.function) (il: list Mach.instruction) (it1p: bool) :=
+  transl_code_rec f il it1p (fun c => OK c).
+
 (** Translation of a whole function.  Note that we must check
   that the generated code contains less than [2^32] instructions,
   otherwise the offset part of the [PC] code pointer could wrap
   around, leading to incorrect executions. *)
 
 Definition transl_function (f: Mach.function) :=
-  do c <- transl_code f f.(Mach.fn_code) false;
+  do c <- transl_code' f f.(Mach.fn_code) false;
   OK (Pallocframe f.(fn_stacksize) f.(fn_link_ofs) ::
       Pmflr GPR0 ::
       Pstw GPR0 (Cint f.(fn_retaddr_ofs)) GPR1 :: c).
diff --git a/powerpc/Asmgenproof.v b/powerpc/Asmgenproof.v
index 658653f..07e66cf 100644
--- a/powerpc/Asmgenproof.v
+++ b/powerpc/Asmgenproof.v
@@ -317,7 +317,8 @@ Lemma transl_find_label:
   end.
 Proof.
   intros. monadInv H. destruct (zlt Int.max_unsigned (list_length_z x)); inv EQ0.
-  monadInv EQ. simpl. eapply transl_code_label; eauto. 
+  monadInv EQ. rewrite transl_code'_transl_code in EQ0.
+  simpl. eapply transl_code_label; eauto. 
 Qed.
 
 End TRANSL_LABEL.
@@ -360,6 +361,7 @@ Proof.
   destruct i; try (intros [A B]; apply A). intros. subst c0. repeat constructor.
 - intros. monadInv H0. 
   destruct (zlt Int.max_unsigned (list_length_z x)); inv EQ0. monadInv EQ.
+  rewrite transl_code'_transl_code in EQ0.
   exists x; exists false; split; auto. unfold fn_code. repeat constructor.
 - exact transf_function_no_overflow.
 Qed.
@@ -421,7 +423,7 @@ Lemma exec_straight_steps:
    exists rs2,
        exec_straight tge tf c rs1 m1' k rs2 m2'
     /\ agree ms2 sp rs2
-    /\ (r11_is_parent ep i = true -> rs2#GPR11 = parent_sp s)) ->
+    /\ (it1_is_parent ep i = true -> rs2#GPR11 = parent_sp s)) ->
   exists st',
   plus step tge (State rs1 m1') E0 st' /\
   match_states (Mach.State s fb sp c ms2 m2) st'.
@@ -440,7 +442,7 @@ Lemma exec_straight_steps_goto:
   Genv.find_funct_ptr ge fb = Some (Internal f) ->
   Mach.find_label lbl f.(Mach.fn_code) = Some c' ->
   transl_code_at_pc ge (rs1 PC) fb f (i :: c) ep tf tc ->
-  r11_is_parent ep i = false ->
+  it1_is_parent ep i = false ->
   (forall k c (TR: transl_instr f i ep k = OK c),
    exists jmp, exists k', exists rs2,
        exec_straight tge tf c rs1 m1' (jmp :: k') rs2 m2'
@@ -897,7 +899,7 @@ Hint Resolve agree_nextinstr agree_set_other: asmgen.
   exploit Mem.storev_extends. eexact G. eexact H2. eauto. eauto. 
   intros [m3' [P Q]].
   (* Execution of function prologue *)
-  monadInv EQ0.
+  monadInv EQ0. rewrite transl_code'_transl_code in EQ1.
   set (rs2 := nextinstr (rs0#GPR1 <- sp #GPR0 <- Vundef)).
   set (rs3 := nextinstr (rs2#GPR0 <- (rs0#LR))).
   set (rs4 := nextinstr rs3).