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/* --------------------------------------------------------------------------
* Lambda Lifter
*
* This is a very simple lambda lifter - it doesn't try to do Johnsson-style
* lambda lifting (yet).
*
* The Hugs 98 system is Copyright (c) Mark P Jones, Alastair Reid, the
* Yale Haskell Group, and the Oregon Graduate Institute of Science and
* Technology, 1994-1999, All rights reserved. It is distributed as
* free software under the license in the file "License", which is
* included in the distribution.
*
* $RCSfile: lift.c,v $
* $Revision: 1.11 $
* $Date: 2000/03/10 20:03:36 $
* ------------------------------------------------------------------------*/
#include "prelude.h"
#include "storage.h"
#include "connect.h"
#include "errors.h"
/* --------------------------------------------------------------------------
* Local function prototypes:
* ------------------------------------------------------------------------*/
static List liftedBinds = NIL;
static Bool makeInlineable = FALSE;
static Int inlineCounter = 0;
static StgExpr abstractExpr ( List vars, StgExpr e );
static inline Bool isTopLevel( StgVar v );
static List filterFreeVars( List vs );
static List liftLetBinds ( List binds, Bool topLevel );
static void liftAlt ( StgCaseAlt alt );
static void liftPrimAlt ( StgPrimAlt alt );
static void liftExpr ( StgExpr e );
/* --------------------------------------------------------------------------
* Lambda lifter
* ------------------------------------------------------------------------*/
/* abstract variables out of an expression */
static StgExpr abstractExpr( List vars, StgExpr e )
{
List args = NIL;
List sub = NIL; /* association list */
for(; nonNull(vars); vars=tl(vars)) {
StgVar var = hd(vars);
StgVar arg = mkStgVar(NIL,NIL);
stgVarRep(arg) = stgVarRep(var);
args = cons(arg,args);
sub = cons(pair(var,arg),sub);
}
return makeStgLambda(rev(args),substExpr(sub,e));
}
/* ToDo: should be conservative estimate but isn't */
/* Will a variable be floated out to top level - conservative estimate? */
static inline Bool isTopLevel( StgVar v )
{
if (isNull(stgVarBody(v))) {
return FALSE; /* only let bound vars can be floated */
} else if (stgVarInfo(v) == NONE) {
return TRUE; /* those at top level are already there */
} else {
return FALSE;
}
}
static List filterFreeVars( List vs )
{
List fvs = NIL;
if (vs == NONE) {
return NIL;
} else {
for(; nonNull(vs); vs=tl(vs)) {
StgVar v = hd(vs);
if (!isTopLevel(v)) {
fvs = cons(v,fvs);
}
}
return fvs;
}
}
static List liftLetBinds( List binds, Bool topLevel )
{
List bs = NIL;
for(; nonNull(binds); binds=tl(binds)) {
StgVar bind = hd(binds);
StgRhs rhs = stgVarBody(bind);
List fvs = filterFreeVars(stgVarInfo(bind));
switch (whatIs(rhs)) {
case STGCON:
case STGAPP:
case STGVAR:
case NAME:
bs = cons(bind,bs);
break;
default:
liftExpr(rhs);
if (nonNull(fvs)) {
StgVar v = mkStgVar(abstractExpr(fvs,rhs),NONE);
liftedBinds = cons(v,liftedBinds);
if (makeInlineable) {
Name n;
char s[16];
sprintf(s,"lam%d",inlineCounter++);
n = newName(findText(s),NIL);
name(n).stgVar = v;
stgVarBody(bind) = makeStgApp(n, fvs);
} else {
stgVarBody(bind) = makeStgApp(v, fvs);
}
}
bs = cons(bind,bs);
break;
}
}
return bs;
}
static void liftAlt( StgCaseAlt alt )
{
if (isDefaultAlt(alt))
liftExpr(stgDefaultBody(alt)); else
liftExpr(stgCaseAltBody(alt));
}
static void liftPrimAlt( StgPrimAlt alt )
{
liftExpr(stgPrimAltBody(alt));
}
static void liftExpr( StgExpr e )
{
switch (whatIs(e)) {
case LETREC:
stgLetBinds(e) = liftLetBinds(stgLetBinds(e),FALSE);
liftExpr(stgLetBody(e));
break;
case LAMBDA:
liftExpr(stgLambdaBody(e));
break;
case CASE:
liftExpr(stgCaseScrut(e));
mapProc(liftAlt,stgCaseAlts(e));
break;
case PRIMCASE:
liftExpr(stgPrimCaseScrut(e));
mapProc(liftPrimAlt,stgPrimCaseAlts(e));
break;
case STGPRIM:
break;
case STGAPP:
break;
case STGVAR:
case NAME:
break;
default:
internal("liftExpr");
}
}
/* Lift a list of top-level binds. */
List liftBinds( List binds )
{
List bs;
for(bs=binds; nonNull(bs); bs=tl(bs)) {
StgVar bind = hd(bs);
if (debugSC) {
if (lastModule() != modulePrelude) {
fprintf(stderr, "\n");
ppStg(hd(bs));
fprintf(stderr, "\n");
}
}
freeVarsBind(NIL,bind);
stgVarInfo(bind) = NONE; /* mark as top level */
}
liftedBinds = NIL;
binds = liftLetBinds(binds,TRUE);
binds = revOnto(liftedBinds,binds);
liftedBinds = NIL;
return binds;
}
/* --------------------------------------------------------------------------
* Compiler control:
* ------------------------------------------------------------------------*/
Void liftControl(what)
Int what; {
switch (what) {
case POSTPREL: break;
case PREPREL:
case RESET:
liftedBinds = NIL;
break;
case MARK:
mark(liftedBinds);
break;
}
}
/*-------------------------------------------------------------------------*/
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