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ack/util/ego/cj/cj.c

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/* $Id$ */
/*
* (c) copyright 1987 by the Vrije Universiteit, Amsterdam, The Netherlands.
* See the copyright notice in the ACK home directory, in the file "Copyright".
*/
/* C R O S S J U M P I N G
*
* CJ.H
*
*/
#include <stdlib.h>
#include <stdio.h>
#include <em_mnem.h>
#include <em_spec.h>
#include "../share/types.h"
#include "../share/debug.h"
#include "../share/global.h"
#include "../share/files.h"
#include "../share/get.h"
#include "../share/put.h"
#include "../share/lset.h"
#include "../share/map.h"
#include "../share/alloc.h"
#include "../share/utils.h"
#include "../share/def.h"
#include "../share/stack_chg.h"
#include "../share/go.h"
/* Cross jumping performs optimzations like:
*
* if cond then goto L1; if cond then goto L1
* S1; -----> S1;
* S2; goto L3;
* goto L2; L1:
* L1: S3;
* S3; L3:
* S2; S2;
* L2:
*
* CJ looks for two basic blocks b1 and b2 with the following properties:
* - there exists a basic block S such that SUCC(b1) = SUCC(b2) = {S}
* (so both have only 1 successor)
* - the last N (N > 0) instructions of b1 and b2, not counting a possible
* BRAnch instruction, are the same.
* As a result of the first condition, at least of the two blocks must end
* on an (unconditional) BRAnch instruction. If both end on a BRA, one block
* is chosen at random. Assume this block is b1. A new label L is put just
* before the N common instructions of block b2 (so this block is split
* into two). The BRA of b1 is changed into a BRA L. So dynamically the same
* instructions are executed in a slightly different order; yet the size of
* the code has become smaller.
*/
STATIC int Scj; /* number of optimizations found */
STATIC void showinstr();
#define DLINK(l1,l2) l1->l_next=l2; l2->l_prev=l1
STATIC bool same_instr(l1,l2)
line_p l1,l2;
{
/* See if l1 and l2 are the same instruction */
if (l1 == 0 || l2 == 0 || TYPE(l1) != TYPE(l2)) return FALSE;
if (INSTR(l1) != INSTR(l2)) return FALSE;
switch(TYPE(l1)) {
case OPSHORT: return SHORT(l1) == SHORT(l2);
case OPOFFSET: return OFFSET(l1) == OFFSET(l2);
case OPPROC: return PROC(l1) == PROC(l2);
case OPOBJECT: return OBJ(l1) == OBJ(l2);
case OPINSTRLAB: return INSTRLAB(l1) == INSTRLAB(l2);
case OPNO: return TRUE;
default: return FALSE;
}
}
STATIC line_p last_mnem(b)
bblock_p b;
{
/* Determine the last line of a list */
register line_p l;
for (l = b->b_start; l->l_next != (line_p) 0; l = l->l_next);
while (l != (line_p) 0 && (INSTR(l) < sp_fmnem || INSTR(l) > sp_lmnem)) {
l = PREV(l);
}
return l;
}
STATIC bool is_desirable(text)
line_p text;
{
/* We avoid to generate a BRAnch in the middle of some expression,
* as the code generator will write the contents of the fakestack
* to the real stack if it encounters a BRA. We do not avoid to
* split the parameter-pushing code of a subroutine call into two,
* as the parameters are pushed on the real stack anyway.
* So e.g. "LOL a ; LOL b; ADI" will not be split, but
* "LOL a; LOL b; CAL f" may be split.
*/
line_p l;
bool ok;
int stack_diff,pop,push;
stack_diff = 0;
for (l = text; l != (line_p) 0; l = l->l_next) {
switch(INSTR(l)) {
case op_cal:
case op_asp:
case op_bra:
return TRUE;
}
line_change(l,&ok,&pop,&push);
/* printf("instr %d, pop %d, push %d, ok %d\n",INSTR(l),pop,push,ok); */
if (!ok || (stack_diff -= pop) < 0) {
return FALSE;
} else {
stack_diff += push;
}
}
return TRUE;
}
STATIC cp_loops(b1,b2)
bblock_p b1,b2;
{
/* Copy the loopset of b2 to b1 */
Lindex i;
loop_p lp;
for (i = Lfirst(b2->b_loops); i != (Lindex) 0;
i = Lnext(i,b2->b_loops)) {
lp = (loop_p) Lelem(i);
Ladd(lp,&b1->b_loops);
}
}
STATIC jump_cross(l1,l2,b1,b2)
line_p l1,l2;
bblock_p b1,b2;
{
/* A cross-jump from block b2 to block b1 is found; the code in
* block b2 from line l2 up to the BRAnch is removed; block b1 is
* split into two; the second part consists of a new label
* followed by the code from l1 till the end of the block.
*/
line_p l;
bblock_p b;
bblock_p s;
/* First adjust the control flow graph */
b = freshblock(); /* create a new basic block */
b->b_succ = b1->b_succ;
/* SUCC(b1) = {b} */
b1->b_succ = Lempty_set(); Ladd(b,&b1->b_succ);
/* SUCC(b2) = {b} */
Ldeleteset(b2->b_succ); b2->b_succ = Lempty_set(); Ladd(b,&b2->b_succ);
/* PRED(b) = {b1,b2} */
b->b_pred = Lempty_set(); Ladd(b1,&b->b_pred); Ladd(b2,&b->b_pred);
/* PRED(SUCC(b)) := PRED(SUCC(b)) - {b1,b2} + {b} */
assert(Lnrelems(b->b_succ) == 1);
s = (bblock_p) Lelem(Lfirst(b->b_succ));
Lremove(b1,&s->b_pred); Lremove(b2,&s->b_pred); Ladd(b,&s->b_pred);
cp_loops(b,b1);
b->b_idom = common_dom(b1,b2);
b->b_flags = b1->b_flags;
b->b_next = b1->b_next;
b1->b_next = b;
/* Now adjust the EM text */
l = PREV(l1);
while (l && INSTR(l) == op_lab) {
l1 = l;
l = PREV(l);
}
if (l == (line_p) 0) {
b1->b_start = (line_p) 0;
} else {
l->l_next = (line_p) 0;
}
if (INSTR(l1) == op_lab) {
l = l1;
}
else {
l = newline(OPINSTRLAB);
l->l_instr = op_lab;
INSTRLAB(l) = freshlabel();
DLINK(l,l1);
}
b->b_start = l;
for (l = l2; INSTR(l) != op_bra;) {
line_p next = l->l_next;
assert (l != (line_p) 0);
rm_line(l,b2);
l = next;
}
INSTRLAB(l) = INSTRLAB(b->b_start);
}
STATIC bool try_tail(b1,b2)
bblock_p b1,b2;
{
/* See if b1 and b2 end on the same sequence of instructions */
line_p l1,l2;
bblock_p b = (bblock_p) 0;
int cnt = 0;
/* printf("try block %d and %d\n",b1->b_id,b2->b_id); */
if (b1->b_start == (line_p) 0 || b2->b_start == (line_p) 0) return FALSE;
l1 = last_mnem(b1);
l2 = last_mnem(b2);
if (l1 == (line_p) 0 || l2 == (line_p) 0) return FALSE;
/* printf("consider:\n"); showinstr(l1); showinstr(l2); */
if (INSTR(l1) == op_bra) {
b = b1;
l1 = PREV(l1);
}
if (INSTR(l2) == op_bra) {
b = b2;
l2 = PREV(l2);
}
assert(b != (bblock_p) 0);
while(same_instr(l1,l2)) {
cnt++;
l1 = PREV(l1);
l2 = PREV(l2);
/* printf("consider:\n"); showinstr(l1); showinstr(l2); */
}
if (cnt >= 1) {
l1 = (l1 == 0 ? b1->b_start : l1->l_next);
l2 = (l2 == 0 ? b2->b_start : l2->l_next);
if (is_desirable(l1)) {
if (b == b1) {
jump_cross(l2,l1,b2,b1);
Scj++;
} else {
jump_cross(l1,l2,b1,b2);
Scj++;
}
return TRUE;
}
}
return FALSE;
}
STATIC bool try_pred(b)
bblock_p b;
{
/* See if there is any pair (b1,b2), both in PRED(b) for
* which we can perform cross jumping.
*/
register bblock_p b1,b2;
register Lindex i,j;
lset s = b->b_pred;
for (i = Lfirst(s); i != (Lindex) 0; i = Lnext(i,s)) {
b1 = (bblock_p) Lelem(i);
if (Lnrelems(b1->b_succ) != 1) continue;
for (j = Lfirst(s); j != (Lindex) 0; j = Lnext(j,s)) {
b2 = (bblock_p) Lelem(j);
if (b1 != b2 && Lnrelems(b2->b_succ) == 1) {
if (try_tail(b1,b2)) return TRUE;
}
}
}
return FALSE;
}
void cj_optimize(void *vp)
{
/* Perform cross jumping for procedure p.
* In case cases a cross-jumping optimization which give
* new opportunities for further cross-jumping optimizations.
* Hence we repeat the whole process for the entire procedure,
* untill we find no further optimizations.
*/
proc_p p = vp;
bblock_p b;
bool changes = TRUE;
if (IS_ENTERED_WITH_GTO(p)) return;
while(changes) {
changes = FALSE;
b = p->p_start;
while (b != (bblock_p) 0) {
if (try_pred(b)) {
changes = TRUE;
} else {
b = b->b_next;
}
}
}
}
main(argc,argv)
int argc;
char *argv[];
{
go(argc,argv,no_action,cj_optimize,no_action,no_action);
report("cross jumps",Scj);
exit(0);
}
/******
* Debugging stuff
*/
extern char em_mnem[]; /* The mnemonics of the EM instructions. */
STATIC void showinstr(lnp) line_p lnp; {
/* Makes the instruction in `lnp' human readable. Only lines that
* can occur in expressions that are going to be eliminated are
* properly handled.
*/
if (lnp == 0) return;
if (INSTR(lnp) < sp_fmnem || INSTR(lnp) > sp_lmnem) {
printf("\t*** ?\n");
return;
}
printf("\t%s", &em_mnem[4 * (INSTR(lnp)-sp_fmnem)]);
switch (TYPE(lnp)) {
case OPNO:
break;
case OPSHORT:
printf(" %d", SHORT(lnp)); break;
case OPOBJECT:
printf(" %d", OBJ(lnp)->o_id); break;
case OPOFFSET:
printf(" %ld", OFFSET(lnp)); break;
default:
printf(" ?"); break;
}
printf("\n");
} /* showinstr */
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