optim.c

来自「<B>Digital的Unix操作系统VAX 4.2源码</B>」· C语言 代码 · 共 299 行

#ifndef lint
static char	*sccsid = " @(#)optim.c	4.1	(ULTRIX)	7/17/90";
#endif lint

/************************************************************************
 *									*
 *			Copyright (c) 1986 by				*
 *		Digital Equipment Corporation, Maynard, MA		*
 *			All rights reserved.				*
 *									*
 *   This software is furnished under a license and may be used and	*
 *   copied  only  in accordance with the terms of such license and	*
 *   with the  inclusion  of  the  above  copyright  notice.   This	*
 *   software  or  any  other copies thereof may not be provided or	*
 *   otherwise made available to any other person.  No title to and	*
 *   ownership of the software is hereby transferred.			*
 *									*
 *   This software is  derived  from  software  received  from  the	*
 *   University    of   California,   Berkeley,   and   from   Bell	*
 *   Laboratories.  Use, duplication, or disclosure is  subject  to	*
 *   restrictions  under  license  agreements  with  University  of	*
 *   California and with AT&T.						*
 *									*
 *   The information in this software is subject to change  without	*
 *   notice  and should not be construed as a commitment by Digital	*
 *   Equipment Corporation.						*
 *									*
 *   Digital assumes no responsibility for the use  or  reliability	*
 *   of its software on equipment which is not supplied by Digital.	*
 *									*
 ************************************************************************/

/************************************************************************
*
*			Modification History
*
*	David Metsky		15-Jan-86
*
* 001	Added from BSD 4.3 version as part of upgrade.
*
*	Based on:	optim.c		4.6		8/22/85
*
*************************************************************************/

# include "pass1.h"

# define SWAP(p,q) {sp=p; p=q; q=sp;}
# define RCON(p) (p->in.right->in.op==ICON)
# define RO(p) p->in.right->in.op
# define RV(p) p->in.right->tn.lval
# define LCON(p) (p->in.left->in.op==ICON)
# define LO(p) p->in.left->in.op
# define LV(p) p->in.left->tn.lval

	/* is p a constant without a name */
# define nncon(p)	((p)->in.op == ICON && (p)->tn.rval == NONAME)

int oflag = 0;

NODE *
fortarg( p ) NODE *p; {
	/* fortran function arguments */

	if( p->in.op == CM ){
		p->in.left = fortarg( p->in.left );
		p->in.right = fortarg( p->in.right );
		return(p);
		}

	while( ISPTR(p->in.type) ){
		p = buildtree( UNARY MUL, p, NIL );
		}
	return( optim(p) );
	}

	/* mapping relationals when the sides are reversed */
short revrel[] ={ EQ, NE, GE, GT, LE, LT, UGE, UGT, ULE, ULT };
NODE *
optim(p) register NODE *p; {
	/* local optimizations, most of which are probably machine independent */

	register o, ty;
	NODE *sp;
	int i;
	TWORD t;

	if( (t=BTYPE(p->in.type))==ENUMTY || t==MOETY ) econvert(p);
	if( oflag ) return(p);
	ty = optype( o=p->in.op);
	if( ty == LTYPE ) return(p);

	if( ty == BITYPE ) p->in.right = optim(p->in.right);
	p->in.left = optim(p->in.left);

	/* collect constants */

	switch(o){

	case SCONV:
	case PCONV:
		return( clocal(p) );

	case FORTCALL:
		p->in.right = fortarg( p->in.right );
		break;

	case UNARY AND:
		if( LO(p) != NAME || !andable(p->in.left) ) return(p);

		LO(p) = ICON;

		setuleft:
		/* paint over the type of the left hand side with the type of the top */
		p->in.left->in.type = p->in.type;
		p->in.left->fn.cdim = p->fn.cdim;
		p->in.left->fn.csiz = p->fn.csiz;
		p->in.op = FREE;
		return( p->in.left );

	case UNARY MUL:
		if( LO(p) != ICON ) break;
		LO(p) = NAME;
		goto setuleft;

	case MINUS:
		if( !nncon(p->in.right) ) break;
		RV(p) = -RV(p);
		o = p->in.op = PLUS;

	case MUL:
	case PLUS:
	case AND:
	case OR:
	case ER:
		/* commutative ops; for now, just collect constants */
		/* someday, do it right */
		if( nncon(p->in.left) || ( LCON(p) && !RCON(p) ) ) SWAP( p->in.left, p->in.right );
		/* make ops tower to the left, not the right */
		if( RO(p) == o ){
			NODE *t1, *t2, *t3;
			t1 = p->in.left;
			sp = p->in.right;
			t2 = sp->in.left;
			t3 = sp->in.right;
			/* now, put together again */
			p->in.left = sp;
			sp->in.left = t1;
			sp->in.right = t2;
			p->in.right = t3;
			}
		if(o == PLUS && LO(p) == MINUS && RCON(p) && RCON(p->in.left) &&
		   conval(p->in.right, MINUS, p->in.left->in.right)){
			zapleft:
			RO(p->in.left) = FREE;
			LO(p) = FREE;
			p->in.left = p->in.left->in.left;
		}
		if( RCON(p) && LO(p)==o && RCON(p->in.left) &&
		    conval( p->in.right, o, p->in.left->in.right ) ){
			goto zapleft;
			}
		else if( LCON(p) && RCON(p) &&
			 conval( p->in.left, o, p->in.right ) ){
			zapright:
			RO(p) = FREE;
			p->in.left = makety( p->in.left, p->in.type, p->fn.cdim, p->fn.csiz );
			p->in.op = FREE;
			return( clocal( p->in.left ) );
			}
		/* FALL THROUGH */

	case ASG MUL:
		/* change muls to adds or shifts */

		if( (o == MUL || o == ASG MUL) &&
		    nncon(p->in.right) && (i=ispow2(RV(p)))>=0){
			if( i == 0 ) /* multiplication by 1 */
				goto zapright;
			if( i == 1 && optype(LO(p)) == LTYPE){
				/* multiplication by 2 */
				p->in.op = (asgop(o) ? ASG PLUS : PLUS);
				o = p->in.op;
				ncopy(p->in.right, p->in.left);
				}
			else {
				p->in.op = (asgop(o) ? ASG LS : LS);
				o = p->in.op;
				p->in.right->in.type = p->in.right->fn.csiz = INT;
				RV(p) = i;
				}
			}

		/* change +'s of negative consts back to - */
		if( o==PLUS && nncon(p->in.right) && RV(p)<0 ){
			RV(p) = -RV(p);
			o = p->in.op = MINUS;
			}
		/* FALL THROUGH */
	case ASG AND:
	case ASG PLUS:
	case ASG MINUS:
	case RS:
	case LS:
		/* Operations with zero */
		if( nncon(p->in.right) && RV(p) == 0 ) {
			if( o == MUL || o == ASG MUL ||
			    o == AND || o == ASG AND ) {
				if( asgop(o) )
					p->in.op = ASSIGN;
				else if( optype(LO(p)) == LTYPE ) {
					p->in.op = FREE;
					LO(p) = FREE;
					p = p->in.right;
					}
				else
					p->in.op = COMOP; /* side effects */
				}
			else if( o == PLUS || o == MINUS ||
				 o == ASG PLUS || o == ASG MINUS ||
				 o == OR || o == ER ||
				 o == LS || o == RS )
				goto zapright;
			}
		break;

	case ASG DIV:
	case DIV:
		if( nncon( p->in.right ) ){
			if( RV(p) == 0 ) uerror("division by zero");
			else if( RV(p) == 1 ) goto zapright;
			/* Unsigned division by a power of two */
			else if( (i=ispow2(RV(p)))>=0 &&
				 (ISUNSIGNED(p->in.left->in.type) ||
				  ISUNSIGNED(p->in.right->in.type)) ){
				p->in.op = (asgop(o) ? ASG RS : RS);
				p->in.right->in.type = p->in.right->fn.csiz = INT;
				RV(p) = i;
				}
			}
		break;

	case ASG MOD:
	case MOD:
		if( nncon(p->in.right) ){
			if( RV(p) == 0 ) uerror("modulus of zero");
			else if( RV(p) == 1 ){ /* mod by one gives zero */
				RV(p) = 0;
				if( asgop(o) )
					p->in.op = ASSIGN;
				else if( optype(LO(p)) == LTYPE ) {
					p->in.op = FREE;
					LO(p) = FREE;
					p = p->in.right;
					}
				else
					p->in.op = COMOP; /* side effects */
				}
			else if ((i=ispow2(RV(p)))>=0 &&
				 (ISUNSIGNED(p->in.left->in.type) ||
				  ISUNSIGNED(p->in.right->in.type)) ){
				/* Unsigned mod by a power of two */
				p->in.op = (asgop(o) ? ASG AND : AND);
				RV(p)--;
				}
			}
		break;

	case EQ:
	case NE:
	case LT:
	case LE:
	case GT:
	case GE:
	case ULT:
	case ULE:
	case UGT:
	case UGE:
		if( !LCON(p) ) break;

		/* exchange operands */

		sp = p->in.left;
		p->in.left = p->in.right;
		p->in.right = sp;
		p->in.op = revrel[p->in.op - EQ ];
		break;

		}

	return(p);
	}

ispow2( c ) CONSZ c; {
	register i;
	if( c <= 0 || (c&(c-1)) ) return(-1);
	for( i=0; c>1; ++i) c >>= 1;
	return(i);
	}