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