script engine: switch() fixup and optimizations

- optimize/transform switch() statements into:
   - jump tables (if small enough)
   - condition tables
   - simple blocks (optimization when the expression in switch()
     is constant)
   - only a condition evaluator (when the switch body is empty,
     but the switch expression has side-effect and hence cannot be
     optimized away)

route.c

@@ -82,6 +82,7 @@
 #include "str_hash.h"
 #include "ut.h"
 #include "rvalue.h"
+#include "switch.h"
 
 #define RT_HASH_SIZE	8 /* route names hash */
 
@@ -697,7 +698,29 @@ int fix_actions(struct action* a)
 						return ret;
 				}
 				break;
-
+			case SWITCH_T:
+				if (t->val[0].type!=RVE_ST){
+					LOG(L_CRIT, "BUG: fix_actions: invalid subtype"
+								"%d for if (should be expr)\n",
+								t->val[0].type);
+					return E_BUG;
+				}else if (t->val[1].type!=CASE_ST){
+					LOG(L_CRIT, "BUG: fix_actions: invalid subtype"
+								"%d for switch(...){...}(should be action)\n",
+								t->val[1].type);
+					return E_BUG;
+				}
+				if (t->val[0].u.data){
+					if ((ret=fix_rval_expr(&t->val[0].u.data))<0)
+						return ret;
+				}else{
+					LOG(L_CRIT, "BUG: fix_actions: null switch()"
+							" expression\n");
+					return E_BUG;
+				}
+				if ((ret=fix_switch(t))<0)
+					return ret;
+				break;
 			case ASSIGN_T:
 			case ADD_T:
 				if (t->val[0].type !=LVAL_ST) {

switch.c

@@ -0,0 +1,374 @@
+/* 
+ * $Id$
+ * 
+ * Copyright (C) 2009 iptelorg GmbH
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+/*
+ * switch.c
+ */
+/*
+ * History:
+ * --------
+ *  2009-02-02  initial version (andrei)
+*/
+
+#include "switch.h"
+#include "rvalue.h"
+#include "route.h"
+#include "mem/mem.h"
+#include "error.h"
+
+#define MAX_JT_SIZE 100  /* maximum jump table size */
+
+
+/** create a cond table structure (pkg_malloc'ed).
+ * @return 0 on error, pointer on success
+ */
+static struct switch_cond_table* mk_switch_cond_table(int n)
+{
+	struct switch_cond_table* sct;
+	
+	/* allocate everything in a single block, better for cache locality */
+	sct=pkg_malloc(ROUND_INT(sizeof(*sct))+
+					ROUND_POINTER(n*sizeof(sct->cond[0]))+
+					n*sizeof(sct->jump[0]));
+	if (sct==0) return 0;
+	sct->n=n;
+	sct->cond=(int*)((char*)sct+ROUND_INT(sizeof(*sct)));
+	sct->jump=(struct action**)
+				((char*)sct->cond+ROUND_POINTER(n*sizeof(sct->cond[0])));
+	sct->def=0;
+	return sct;
+}
+
+
+
+/** create a jump table structure (pkg_malloc'ed).
+ * @param jmp_size - size of the jump table
+ * @param rest - size of the fallback condition table
+ * @return 0 on error, pointer on success
+ */
+static struct switch_jmp_table* mk_switch_jmp_table(int jmp_size, int rest)
+{
+	struct switch_jmp_table* jt;
+	int size;
+	
+	/* alloc everything in a block */
+	size = 	ROUND_POINTER(sizeof(*jt))+
+			ROUND_INT(jmp_size*sizeof(jt->tbl[0]))+
+			ROUND_POINTER(rest*sizeof(jt->rest.cond[0]))+
+			rest*sizeof(jt->rest.jump[0]);
+	jt=pkg_malloc(size);
+	if (jt == 0) return 0;
+	memset(jt, 0, size);
+	jt->tbl = (struct action**)((char*) jt + ROUND_POINTER(sizeof(*jt)));
+	jt->rest.cond = (int*)
+					((char*) jt->tbl + ROUND_INT(jmp_size*sizeof(jt->tbl[0])));
+	jt->rest.jump = (struct action**) ((char*) jt->rest.cond + 
+								ROUND_POINTER(rest*sizeof(jt->rest.cond[0])));
+	jt->rest.n=rest;
+	return jt;
+}
+
+
+
+void destroy_case_stms(struct case_stms *lst)
+{
+	struct case_stms* l;
+	struct case_stms* n;
+	
+	for (l=lst; l; l=n){
+		n=l->next;
+		rve_destroy(l->ct_rve);
+		/* TODO: the action list is not freed (missing destroy_action() and
+		   there are some case when we need at least part of the action list
+		*/
+		pkg_free(l);
+	}
+}
+
+
+
+/** fixup function for SWITCH_T actions.
+ * can produce 4 different action types:
+ *  - BLOCK_T (actions) - actions grouped in a block, break ends the block
+ *    execution.
+ *  - EVAL_T (cond)  - null switch block, but the condition has to be
+ *                       evaluated due to possible side-effects.
+ *  - SWITCH_COND_T(cond, jumps) - condition table
+ *  - SWITCH_JT_T(cond, jumptable) - jumptable + condition table
+ * TODO: external optimizers that would "flatten" BLOCK_T w/no breaks or
+ * breaks at the end.
+ * 
+ */
+int fix_switch(struct action* t)
+{
+	struct case_stms* c;
+	int n, i, j, ret, val;
+	struct action* a;
+	struct action* block;
+	struct action* def_a;
+	struct action* action_lst;
+	struct action** tail;
+	struct switch_jmp_table* jmp;
+	struct switch_cond_table* sct;
+	int labels_no;
+	struct action** def_jmp_bm;
+	int* cond;
+	struct action*** jmp_bm;
+	int default_found;
+	int first, last, start, end, hits, best_hits;
+	struct rval_expr* sw_rve;
+	
+	ret=E_BUG;
+	cond=0;
+	jmp_bm=0;
+	def_jmp_bm=0;
+	labels_no=0;
+	default_found=0;
+	sw_rve=(struct rval_expr*)t->val[0].u.data;
+	/*  handle null actions: optimize away if no
+	   sideffects */
+	if (t->val[1].u.data==0){
+		if (!rve_has_side_effects(sw_rve)){
+			t->type=BLOCK_T;
+			rve_destroy(sw_rve);
+			t->val[0].type=BLOCK_ST;
+			t->val[0].u.data=0;
+			DBG("SWITCH: null switch optimized away\n");
+		}else{
+			t->type=EVAL_T;
+			t->val[0].type=RVE_ST;
+			DBG("SWITCH: null switch turned to EVAL_T\n");
+		}
+		return 0;
+	}
+	def_a=0;
+	n=0;
+	for (c=(struct case_stms*)t->val[1].u.data; c; c=c->next){
+		if (c->ct_rve){
+			if (!rve_is_constant(c->ct_rve)){
+				LOG(L_ERR, "ERROR: fix_switch: non constant "
+						"expression in case\n");
+				return E_BUG;
+			}
+			if (rval_expr_eval_int(0, 0,  &c->int_label, c->ct_rve)
+					<0){
+				LOG(L_ERR, "ERROR: fix_switch: case expression"
+						" (%d,%d) has non-interger type\n",
+						c->ct_rve->fpos.s_line,
+						c->ct_rve->fpos.s_col);
+				return E_BUG;
+			}
+			c->is_default=0;
+			n++; /* count only non-default cases */
+		}else{
+			if (default_found){
+				LOG(L_ERR, "ERROR: fix_switch: more then one \"default\""
+						" label found (%d, %d)\n",
+						c->ct_rve->fpos.s_line,
+						c->ct_rve->fpos.s_col);
+				return E_UNSPEC;
+			}
+			default_found=1;
+			c->int_label=-1;
+			c->is_default=1;
+			def_a=c->actions;
+		}
+		if ( c->actions && ((ret=fix_actions(c->actions))<0))
+			goto error;
+	}
+	DBG("SWITCH: %d cases, %d default\n", n, default_found);
+	/*: handle n==0 (no case only a default:) */
+	if (n==0){
+		if (default_found){
+			if (!rve_has_side_effects(sw_rve)){
+				t->type=BLOCK_T;
+				rve_destroy(sw_rve);
+				destroy_case_stms(t->val[1].u.data);
+				t->val[0].type=BLOCK_ST;
+				t->val[0].u.data=def_a;
+				t->val[1].type=0;
+				t->val[1].u.data=0;
+				DBG("SWITCH: default only switch optimized away (BLOCK_T)\n");
+				return 0;
+			}
+			DBG("SWITCH: default only switch with side-effect...\n");
+		}else{
+			LOG(L_CRIT, "BUG: fix_switch: empty switch not expected at this"
+					" point\n");
+			ret=E_BUG;
+			goto error;
+		}
+	}
+	labels_no=n;
+	cond=pkg_malloc(sizeof(cond[0])*n);
+	jmp_bm=pkg_malloc(sizeof(jmp_bm[0])*n);
+	if (cond==0 || jmp_bm==0){
+		LOG(L_ERR, "ERROR: fix_switch: memory allocation failure\n");
+		ret=E_OUT_OF_MEM;
+		goto error;
+	}
+	
+	/* fill condition table and jump point bookmarks and "flatten" the action 
+	   lists (transform them into a single list for the entire switch, rather
+	    then one block per case ) */
+	n=0;
+	action_lst=0;
+	tail=&action_lst;
+	for (c=(struct case_stms*)t->val[1].u.data; c; c=c->next){
+		a=c->actions;
+		if (a){
+			for (; a->next; a=a->next);
+			if (action_lst==0)
+				action_lst=c->actions;
+			else
+				*tail=c->actions;
+		}
+		if (c->is_default){
+			def_jmp_bm=tail;
+		} else {
+			for (j=0; j<n; j++){
+				if (cond[j]==c->int_label){
+					LOG(L_ERR, "ERROR: fix_switch: duplicate case (%d,%d)\n",
+							c->ct_rve->fpos.s_line, c->ct_rve->fpos.s_col);
+					ret=E_UNSPEC;
+					goto error;
+				}
+			}
+			cond[n]=c->int_label;
+			jmp_bm[n]=tail;
+			n++;
+		}
+		if (c->actions)
+			tail=&a->next;
+	}
+	/* handle constant rve w/ no side-effects: replace the whole case 
+	   with the case rve block */
+	if ( (scr_opt_lev>=2) &&
+			!rve_has_side_effects(sw_rve) && rve_is_constant(sw_rve)){
+		if (rval_expr_eval_int(0, 0,  &val, sw_rve) <0){
+			LOG(L_ERR, "ERROR: fix_switch: wrong type for switch(...) "
+					"expression (%d,%d)\n", 
+					sw_rve->fpos.s_line, sw_rve->fpos.s_col);
+			ret=E_UNSPEC;
+			goto error;
+		}
+		/* start with the "default:" value in case nothing is found */
+		block=def_jmp_bm?*def_jmp_bm:0;
+		for (i=0; i<n; i++){
+			if (cond[i]==val){
+				block=*jmp_bm[i];
+				break;
+			}
+		}
+		t->type=BLOCK_T;
+		rve_destroy(sw_rve);
+		t->val[0].type=BLOCK_ST;
+		t->val[0].u.data=block;
+		destroy_case_stms(t->val[1].u.data);
+		t->val[1].type=0;
+		t->val[1].u.data=0;
+		ret=0;
+		DBG("SWITCH: constant switch(%d) with %d cases optimized away to case "
+				" %d \n", val, n, i);
+		goto end;
+	}
+	/* try to create a jumptable */
+	/* cost: 2 cmp & table lookup
+	   => makes sense for more then 3 cases
+	   & if size< MAX_JT_SIZE
+	*/
+	best_hits=3; /* more then 3 hits needed */
+	start=end=0;
+	for (i=0; i<n; i++){
+		last=first=cond[i];
+		hits=1;
+		for (j=0; j<n; j++){
+			if ((i==j) || (cond[j]<=first)) continue;
+			if (cond[j]<last)
+				hits++;
+			else if ((cond[j]-first)<MAX_JT_SIZE){
+				last=cond[j];
+				hits++;
+			}
+		}
+		if (hits>best_hits){
+			best_hits=hits;
+			start=first;
+			end=last;
+			if (hits==n) break;
+		}
+	}
+	if (start!=end){
+		/* build jumptable: end-start entries and
+		 with a n-best_hits normal switch table */
+		jmp=mk_switch_jmp_table(end-start+1, n-best_hits);
+		if (jmp==0){
+			LOG(L_ERR, "ERROR: fix_switch: memory allocation error\n");
+			ret=E_OUT_OF_MEM;
+			goto error;
+		}
+		jmp->first=start;
+		jmp->last=end;
+		jmp->rest.n=n-best_hits;
+		jmp->rest.def=def_jmp_bm?*def_jmp_bm:0;
+		/* fill it with default values */
+		for (i=0; i<=(end-start); i++)
+			jmp->tbl[i]=jmp->rest.def;
+		for (i=0, j=0; i<n; i++){
+			if (cond[i]>=start && cond[i]<=end){
+				jmp->tbl[cond[i]-start]=*jmp_bm[i];
+			}else{
+				jmp->rest.cond[j]=cond[i];
+				jmp->rest.jump[j]=*jmp_bm[i];
+				j++;
+			}
+		}
+		t->type=SWITCH_JT_T;
+		t->val[1].type=JUMPTABLE_ST;
+		t->val[1].u.data=jmp;
+		ret=0;
+		DBG("SWITCH: optimized to jumptable [%d, %d] and %d condtable,"
+				"default: %s\n ",
+				jmp->first, jmp->last, jmp->rest.n, jmp->rest.def?"yes":"no");
+	}else{
+		sct=mk_switch_cond_table(n);
+		if (sct==0){
+			LOG(L_ERR, "ERROR: fix_switch: memory allocation error\n");
+			ret=E_OUT_OF_MEM;
+			goto error;
+		}
+		sct->n=n;
+		for (i=0; i<n; i++){
+			sct->cond[i]=cond[i];
+			sct->jump[i]=*jmp_bm[i];
+		}
+		sct->def=def_jmp_bm?*def_jmp_bm:0;
+		t->type=SWITCH_COND_T;
+		t->val[1].type=CONDTABLE_ST;
+		t->val[1].u.data=sct;
+		DBG("SWITCH: optimized to condtable (%d) default: %s\n ",
+				sct->n, sct->def?"yes":"no");
+		ret=0;
+	}
+end:
+error:
+	if (cond) pkg_free(cond);
+	if (jmp_bm) pkg_free(jmp_bm);
+	return ret;
+}
+
+/* vi: set ts=4 sw=4 tw=79:ai:cindent: */