Source

go / src / cmd / 8g / peep.c

  1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
// Derived from Inferno utils/6c/peep.c
// http://code.google.com/p/inferno-os/source/browse/utils/6c/peep.c
//
//	Copyright © 1994-1999 Lucent Technologies Inc.  All rights reserved.
//	Portions Copyright © 1995-1997 C H Forsyth (forsyth@terzarima.net)
//	Portions Copyright © 1997-1999 Vita Nuova Limited
//	Portions Copyright © 2000-2007 Vita Nuova Holdings Limited (www.vitanuova.com)
//	Portions Copyright © 2004,2006 Bruce Ellis
//	Portions Copyright © 2005-2007 C H Forsyth (forsyth@terzarima.net)
//	Revisions Copyright © 2000-2007 Lucent Technologies Inc. and others
//	Portions Copyright © 2009 The Go Authors.  All rights reserved.
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.

#include <u.h>
#include <libc.h>
#include "gg.h"
#include "opt.h"

#define	REGEXT	0

static void	conprop(Reg *r);
static void elimshortmov(Reg *r);

// do we need the carry bit
static int
needc(Prog *p)
{
	while(p != P) {
		switch(p->as) {
		case AADCL:
		case ASBBL:
		case ARCRB:
		case ARCRW:
		case ARCRL:
			return 1;
		case AADDB:
		case AADDW:
		case AADDL:
		case ASUBB:
		case ASUBW:
		case ASUBL:
		case AJMP:
		case ARET:
		case ACALL:
			return 0;
		default:
			if(p->to.type == D_BRANCH)
				return 0;
		}
		p = p->link;
	}
	return 0;
}

static Reg*
rnops(Reg *r)
{
	Prog *p;
	Reg *r1;

	if(r != R)
	for(;;) {
		p = r->prog;
		if(p->as != ANOP || p->from.type != D_NONE || p->to.type != D_NONE)
			break;
		r1 = uniqs(r);
		if(r1 == R)
			break;
		r = r1;
	}
	return r;
}

void
peep(void)
{
	Reg *r, *r1, *r2;
	Prog *p, *p1;
	int t;

	/*
	 * complete R structure
	 */
	t = 0;
	for(r=firstr; r!=R; r=r1) {
		r1 = r->link;
		if(r1 == R)
			break;
		p = r->prog->link;
		while(p != r1->prog)
		switch(p->as) {
		default:
			r2 = rega();
			r->link = r2;
			r2->link = r1;

			r2->prog = p;
			p->reg = r2;

			r2->p1 = r;
			r->s1 = r2;
			r2->s1 = r1;
			r1->p1 = r2;

			r = r2;
			t++;

		case ADATA:
		case AGLOBL:
		case ANAME:
		case ASIGNAME:
			p = p->link;
		}
	}
  
	// byte, word arithmetic elimination.
	elimshortmov(r);

	// constant propagation
	// find MOV $con,R followed by
	// another MOV $con,R without
	// setting R in the interim
	for(r=firstr; r!=R; r=r->link) {
		p = r->prog;
		switch(p->as) {
		case ALEAL:
			if(regtyp(&p->to))
			if(p->from.sym != S)
				conprop(r);
			break;

		case AMOVB:
		case AMOVW:
		case AMOVL:
			if(regtyp(&p->to))
			if(p->from.type == D_CONST)
				conprop(r);
			break;
		}
	}

loop1:
	if(debug['P'] && debug['v'])
		dumpit("loop1", firstr);

	t = 0;
	for(r=firstr; r!=R; r=r->link) {
		p = r->prog;
		switch(p->as) {
		case AMOVL:
			if(regtyp(&p->to))
			if(regtyp(&p->from)) {
				if(copyprop(r)) {
					excise(r);
					t++;
				} else
				if(subprop(r) && copyprop(r)) {
					excise(r);
					t++;
				}
			}
			break;

		case AMOVBLZX:
		case AMOVWLZX:
		case AMOVBLSX:
		case AMOVWLSX:
			if(regtyp(&p->to)) {
				r1 = rnops(uniqs(r));
				if(r1 != R) {
					p1 = r1->prog;
					if(p->as == p1->as && p->to.type == p1->from.type){
						p1->as = AMOVL;
						t++;
					}
				}
			}
			break;

		case AADDL:
		case AADDW:
			if(p->from.type != D_CONST || needc(p->link))
				break;
			if(p->from.offset == -1){
				if(p->as == AADDL)
					p->as = ADECL;
				else
					p->as = ADECW;
				p->from = zprog.from;
				break;
			}
			if(p->from.offset == 1){
				if(p->as == AADDL)
					p->as = AINCL;
				else
					p->as = AINCW;
				p->from = zprog.from;
				break;
			}
			break;

		case ASUBL:
		case ASUBW:
			if(p->from.type != D_CONST || needc(p->link))
				break;
			if(p->from.offset == -1) {
				if(p->as == ASUBL)
					p->as = AINCL;
				else
					p->as = AINCW;
				p->from = zprog.from;
				break;
			}
			if(p->from.offset == 1){
				if(p->as == ASUBL)
					p->as = ADECL;
				else
					p->as = ADECW;
				p->from = zprog.from;
				break;
			}
			break;
		}
	}
	if(t)
		goto loop1;
}

void
excise(Reg *r)
{
	Prog *p;

	p = r->prog;
	if(debug['P'] && debug['v'])
		print("%P ===delete===\n", p);

	p->as = ANOP;
	p->from = zprog.from;
	p->to = zprog.to;

	ostats.ndelmov++;
}

Reg*
uniqp(Reg *r)
{
	Reg *r1;

	r1 = r->p1;
	if(r1 == R) {
		r1 = r->p2;
		if(r1 == R || r1->p2link != R)
			return R;
	} else
		if(r->p2 != R)
			return R;
	return r1;
}

Reg*
uniqs(Reg *r)
{
	Reg *r1;

	r1 = r->s1;
	if(r1 == R) {
		r1 = r->s2;
		if(r1 == R)
			return R;
	} else
		if(r->s2 != R)
			return R;
	return r1;
}

int
regtyp(Adr *a)
{
	int t;

	t = a->type;
	if(t >= D_AX && t <= D_DI)
		return 1;
	return 0;
}

// movb elimination.
// movb is simulated by the linker
// when a register other than ax, bx, cx, dx
// is used, so rewrite to other instructions
// when possible.  a movb into a register
// can smash the entire 64-bit register without
// causing any trouble.
static void
elimshortmov(Reg *r)
{
	Prog *p;

	for(r=firstr; r!=R; r=r->link) {
		p = r->prog;
		if(regtyp(&p->to)) {
			switch(p->as) {
			case AINCB:
			case AINCW:
				p->as = AINCL;
				break;
			case ADECB:
			case ADECW:
				p->as = ADECL;
				break;
			case ANEGB:
			case ANEGW:
				p->as = ANEGL;
				break;
			case ANOTB:
			case ANOTW:
				p->as = ANOTL;
				break;
			}
			if(regtyp(&p->from) || p->from.type == D_CONST) {
				// move or artihmetic into partial register.
				// from another register or constant can be movl.
				// we don't switch to 32-bit arithmetic if it can
				// change how the carry bit is set (and the carry bit is needed).
				switch(p->as) {
				case AMOVB:
				case AMOVW:
					p->as = AMOVL;
					break;
				case AADDB:
				case AADDW:
					if(!needc(p->link))
						p->as = AADDL;
					break;
				case ASUBB:
				case ASUBW:
					if(!needc(p->link))
						p->as = ASUBL;
					break;
				case AMULB:
				case AMULW:
					p->as = AMULL;
					break;
				case AIMULB:
				case AIMULW:
					p->as = AIMULL;
					break;
				case AANDB:
				case AANDW:
					p->as = AANDL;
					break;
				case AORB:
				case AORW:
					p->as = AORL;
					break;
				case AXORB:
				case AXORW:
					p->as = AXORL;
					break;
				case ASHLB:
				case ASHLW:
					p->as = ASHLL;
					break;
				}
			} else {
				// explicit zero extension
				switch(p->as) {
				case AMOVB:
					p->as = AMOVBLZX;
					break;
				case AMOVW:
					p->as = AMOVWLZX;
					break;
				}
			}
		}
	}
}

/*
 * the idea is to substitute
 * one register for another
 * from one MOV to another
 *	MOV	a, R0
 *	ADD	b, R0	/ no use of R1
 *	MOV	R0, R1
 * would be converted to
 *	MOV	a, R1
 *	ADD	b, R1
 *	MOV	R1, R0
 * hopefully, then the former or latter MOV
 * will be eliminated by copy propagation.
 */
int
subprop(Reg *r0)
{
	Prog *p;
	Adr *v1, *v2;
	Reg *r;
	int t;

	p = r0->prog;
	v1 = &p->from;
	if(!regtyp(v1))
		return 0;
	v2 = &p->to;
	if(!regtyp(v2))
		return 0;
	for(r=uniqp(r0); r!=R; r=uniqp(r)) {
		if(uniqs(r) == R)
			break;
		p = r->prog;
		switch(p->as) {
		case ACALL:
			return 0;

		case AIMULL:
		case AIMULW:
			if(p->to.type != D_NONE)
				break;

		case ARCLB:
		case ARCLL:
		case ARCLW:
		case ARCRB:
		case ARCRL:
		case ARCRW:
		case AROLB:
		case AROLL:
		case AROLW:
		case ARORB:
		case ARORL:
		case ARORW:
		case ASALB:
		case ASALL:
		case ASALW:
		case ASARB:
		case ASARL:
		case ASARW:
		case ASHLB:
		case ASHLL:
		case ASHLW:
		case ASHRB:
		case ASHRL:
		case ASHRW:
			if(p->from.type == D_CONST)
				break;

		case ADIVB:
		case ADIVL:
		case ADIVW:
		case AIDIVB:
		case AIDIVL:
		case AIDIVW:
		case AIMULB:
		case AMULB:
		case AMULL:
		case AMULW:

		case AREP:
		case AREPN:

		case ACWD:
		case ACDQ:

		case ASTOSB:
		case ASTOSL:
		case AMOVSB:
		case AMOVSL:
			return 0;

		case AMOVL:
			if(p->to.type == v1->type)
				goto gotit;
			break;
		}
		if(copyau(&p->from, v2) ||
		   copyau(&p->to, v2))
			break;
		if(copysub(&p->from, v1, v2, 0) ||
		   copysub(&p->to, v1, v2, 0))
			break;
	}
	return 0;

gotit:
	copysub(&p->to, v1, v2, 1);
	if(debug['P']) {
		print("gotit: %D->%D\n%P", v1, v2, r->prog);
		if(p->from.type == v2->type)
			print(" excise");
		print("\n");
	}
	for(r=uniqs(r); r!=r0; r=uniqs(r)) {
		p = r->prog;
		copysub(&p->from, v1, v2, 1);
		copysub(&p->to, v1, v2, 1);
		if(debug['P'])
			print("%P\n", r->prog);
	}
	t = v1->type;
	v1->type = v2->type;
	v2->type = t;
	if(debug['P'])
		print("%P last\n", r->prog);
	return 1;
}

/*
 * The idea is to remove redundant copies.
 *	v1->v2	F=0
 *	(use v2	s/v2/v1/)*
 *	set v1	F=1
 *	use v2	return fail
 *	-----------------
 *	v1->v2	F=0
 *	(use v2	s/v2/v1/)*
 *	set v1	F=1
 *	set v2	return success
 */
int
copyprop(Reg *r0)
{
	Prog *p;
	Adr *v1, *v2;
	Reg *r;

	p = r0->prog;
	v1 = &p->from;
	v2 = &p->to;
	if(copyas(v1, v2))
		return 1;
	for(r=firstr; r!=R; r=r->link)
		r->active = 0;
	return copy1(v1, v2, r0->s1, 0);
}

int
copy1(Adr *v1, Adr *v2, Reg *r, int f)
{
	int t;
	Prog *p;

	if(r->active) {
		if(debug['P'])
			print("act set; return 1\n");
		return 1;
	}
	r->active = 1;
	if(debug['P'])
		print("copy %D->%D f=%d\n", v1, v2, f);
	for(; r != R; r = r->s1) {
		p = r->prog;
		if(debug['P'])
			print("%P", p);
		if(!f && uniqp(r) == R) {
			f = 1;
			if(debug['P'])
				print("; merge; f=%d", f);
		}
		t = copyu(p, v2, A);
		switch(t) {
		case 2:	/* rar, cant split */
			if(debug['P'])
				print("; %D rar; return 0\n", v2);
			return 0;

		case 3:	/* set */
			if(debug['P'])
				print("; %D set; return 1\n", v2);
			return 1;

		case 1:	/* used, substitute */
		case 4:	/* use and set */
			if(f) {
				if(!debug['P'])
					return 0;
				if(t == 4)
					print("; %D used+set and f=%d; return 0\n", v2, f);
				else
					print("; %D used and f=%d; return 0\n", v2, f);
				return 0;
			}
			if(copyu(p, v2, v1)) {
				if(debug['P'])
					print("; sub fail; return 0\n");
				return 0;
			}
			if(debug['P'])
				print("; sub %D/%D", v2, v1);
			if(t == 4) {
				if(debug['P'])
					print("; %D used+set; return 1\n", v2);
				return 1;
			}
			break;
		}
		if(!f) {
			t = copyu(p, v1, A);
			if(!f && (t == 2 || t == 3 || t == 4)) {
				f = 1;
				if(debug['P'])
					print("; %D set and !f; f=%d", v1, f);
			}
		}
		if(debug['P'])
			print("\n");
		if(r->s2)
			if(!copy1(v1, v2, r->s2, f))
				return 0;
	}
	return 1;
}

/*
 * return
 * 1 if v only used (and substitute),
 * 2 if read-alter-rewrite
 * 3 if set
 * 4 if set and used
 * 0 otherwise (not touched)
 */
int
copyu(Prog *p, Adr *v, Adr *s)
{

	switch(p->as) {

	default:
		if(debug['P'])
			print("unknown op %A\n", p->as);
		/* SBBL; ADCL; FLD1; SAHF */
		return 2;


	case ANEGB:
	case ANEGW:
	case ANEGL:
	case ANOTB:
	case ANOTW:
	case ANOTL:
		if(copyas(&p->to, v))
			return 2;
		break;

	case ALEAL:	/* lhs addr, rhs store */
		if(copyas(&p->from, v))
			return 2;


	case ANOP:	/* rhs store */
	case AMOVL:
	case AMOVBLSX:
	case AMOVBLZX:
	case AMOVWLSX:
	case AMOVWLZX:
		if(copyas(&p->to, v)) {
			if(s != A)
				return copysub(&p->from, v, s, 1);
			if(copyau(&p->from, v))
				return 4;
			return 3;
		}
		goto caseread;

	case ARCLB:
	case ARCLL:
	case ARCLW:
	case ARCRB:
	case ARCRL:
	case ARCRW:
	case AROLB:
	case AROLL:
	case AROLW:
	case ARORB:
	case ARORL:
	case ARORW:
	case ASALB:
	case ASALL:
	case ASALW:
	case ASARB:
	case ASARL:
	case ASARW:
	case ASHLB:
	case ASHLL:
	case ASHLW:
	case ASHRB:
	case ASHRL:
	case ASHRW:
		if(copyas(&p->to, v))
			return 2;
		if(copyas(&p->from, v))
			if(p->from.type == D_CX)
				return 2;
		goto caseread;

	case AADDB:	/* rhs rar */
	case AADDL:
	case AADDW:
	case AANDB:
	case AANDL:
	case AANDW:
	case ADECL:
	case ADECW:
	case AINCL:
	case AINCW:
	case ASUBB:
	case ASUBL:
	case ASUBW:
	case AORB:
	case AORL:
	case AORW:
	case AXORB:
	case AXORL:
	case AXORW:
	case AMOVB:
	case AMOVW:
		if(copyas(&p->to, v))
			return 2;
		goto caseread;

	case ACMPL:	/* read only */
	case ACMPW:
	case ACMPB:
	caseread:
		if(s != A) {
			if(copysub(&p->from, v, s, 1))
				return 1;
			return copysub(&p->to, v, s, 1);
		}
		if(copyau(&p->from, v))
			return 1;
		if(copyau(&p->to, v))
			return 1;
		break;

	case AJGE:	/* no reference */
	case AJNE:
	case AJLE:
	case AJEQ:
	case AJHI:
	case AJLS:
	case AJMI:
	case AJPL:
	case AJGT:
	case AJLT:
	case AJCC:
	case AJCS:

	case AADJSP:
	case AWAIT:
	case ACLD:
		break;

	case AIMULL:
	case AIMULW:
		if(p->to.type != D_NONE) {
			if(copyas(&p->to, v))
				return 2;
			goto caseread;
		}

	case ADIVB:
	case ADIVL:
	case ADIVW:
	case AIDIVB:
	case AIDIVL:
	case AIDIVW:
	case AIMULB:
	case AMULB:
	case AMULL:
	case AMULW:

	case ACWD:
	case ACDQ:
		if(v->type == D_AX || v->type == D_DX)
			return 2;
		goto caseread;

	case AREP:
	case AREPN:
		if(v->type == D_CX)
			return 2;
		goto caseread;

	case AMOVSB:
	case AMOVSL:
		if(v->type == D_DI || v->type == D_SI)
			return 2;
		goto caseread;

	case ASTOSB:
	case ASTOSL:
		if(v->type == D_AX || v->type == D_DI)
			return 2;
		goto caseread;

	case AJMP:	/* funny */
		if(s != A) {
			if(copysub(&p->to, v, s, 1))
				return 1;
			return 0;
		}
		if(copyau(&p->to, v))
			return 1;
		return 0;

	case ARET:	/* funny */
		if(v->type == REGRET || v->type == FREGRET)
			return 2;
		if(s != A)
			return 1;
		return 3;

	case ACALL:	/* funny */
		if(REGEXT && v->type <= REGEXT && v->type > exregoffset)
			return 2;
		if(REGARG >= 0 && v->type == (uchar)REGARG)
			return 2;

		if(s != A) {
			if(copysub(&p->to, v, s, 1))
				return 1;
			return 0;
		}
		if(copyau(&p->to, v))
			return 4;
		return 3;

	case ATEXT:	/* funny */
		if(REGARG >= 0 && v->type == (uchar)REGARG)
			return 3;
		return 0;
	}
	return 0;
}

/*
 * direct reference,
 * could be set/use depending on
 * semantics
 */
int
copyas(Adr *a, Adr *v)
{
	if(a->type != v->type)
		return 0;
	if(regtyp(v))
		return 1;
	if(v->type == D_AUTO || v->type == D_PARAM)
		if(v->offset == a->offset)
			return 1;
	return 0;
}

/*
 * either direct or indirect
 */
int
copyau(Adr *a, Adr *v)
{

	if(copyas(a, v))
		return 1;
	if(regtyp(v)) {
		if(a->type-D_INDIR == v->type)
			return 1;
		if(a->index == v->type)
			return 1;
	}
	return 0;
}

/*
 * substitute s for v in a
 * return failure to substitute
 */
int
copysub(Adr *a, Adr *v, Adr *s, int f)
{
	int t;

	if(copyas(a, v)) {
		t = s->type;
		if(t >= D_AX && t <= D_DI) {
			if(f)
				a->type = t;
		}
		return 0;
	}
	if(regtyp(v)) {
		t = v->type;
		if(a->type == t+D_INDIR) {
			if((s->type == D_BP) && a->index != D_NONE)
				return 1;	/* can't use BP-base with index */
			if(f)
				a->type = s->type+D_INDIR;
//			return 0;
		}
		if(a->index == t) {
			if(f)
				a->index = s->type;
			return 0;
		}
		return 0;
	}
	return 0;
}

static void
conprop(Reg *r0)
{
	Reg *r;
	Prog *p, *p0;
	int t;
	Adr *v0;

	p0 = r0->prog;
	v0 = &p0->to;
	r = r0;

loop:
	r = uniqs(r);
	if(r == R || r == r0)
		return;
	if(uniqp(r) == R)
		return;

	p = r->prog;
	t = copyu(p, v0, A);
	switch(t) {
	case 0:	// miss
	case 1:	// use
		goto loop;

	case 2:	// rar
	case 4:	// use and set
		break;

	case 3:	// set
		if(p->as == p0->as)
		if(p->from.type == p0->from.type)
		if(p->from.node == p0->from.node)
		if(p->from.offset == p0->from.offset)
		if(p->from.scale == p0->from.scale)
		if(p->from.dval == p0->from.dval)
		if(p->from.index == p0->from.index) {
			excise(r);
			goto loop;
		}
		break;
	}
}