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optimization for `while' (first version)

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Roberto Ierusalimschy
2002-05-10 14:02:32 -03:00
parent 94e5545806
commit b487975344
3 changed files with 64 additions and 15 deletions
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47
lparser.c
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@@ -1,5 +1,5 @@
/*
** $Id: lparser.c,v 1.178 2002/04/24 20:07:46 roberto Exp roberto $
** $Id: lparser.c,v 1.179 2002/05/07 17:36:56 roberto Exp roberto $
** Lua Parser
** See Copyright Notice in lua.h
*/
@@ -946,22 +946,61 @@ static void assignment (LexState *ls, struct LHS_assign *lh, int nvars) {
static void cond (LexState *ls, expdesc *v) {
/* cond -> exp */
expr(ls, v); /* read condition */
if (v->k == VNIL) v->k = VFALSE; /* `falses' are all equal here */
luaK_goiftrue(ls->fs, v);
luaK_patchtohere(ls->fs, v->t);
}
/*
** The while statement optimizes its code by coding the condition
** after its body (and thus avoiding one jump in the loop).
*/
/*
** maximum size of expressions for optimizing `while' code
*/
#ifndef MAXEXPWHILE
#define MAXEXPWHILE 100
#endif
/*
** the call `luaK_goiffalse' may grow the size of an expression by
** at most this:
*/
#define EXTRAEXP 5
static void whilestat (LexState *ls, int line) {
/* whilestat -> WHILE cond DO block END */
Instruction codeexp[MAXEXPWHILE + EXTRAEXP];
int lineexp = 0;
int i;
int sizeexp;
FuncState *fs = ls->fs;
int while_init = luaK_getlabel(fs);
expdesc v;
BlockCnt bl;
enterblock(fs, &bl, 1);
next(ls);
cond(ls, &v);
expr(ls, &v);
if (v.k == VK) v.k = VTRUE; /* `trues' are all equal here */
lineexp = ls->linenumber;
luaK_goiffalse(fs, &v);
sizeexp = fs->pc - while_init;
if (sizeexp > MAXEXPWHILE)
luaX_syntaxerror(ls, "while condition too complex");
fs->pc = while_init; /* remove `exp' code */
luaK_getlabel(fs);
for (i = 0; i < sizeexp; i++) /* save `exp' code */
codeexp[i] = fs->f->code[while_init + i];
luaK_jump(fs);
enterblock(fs, &bl, 1);
check(ls, TK_DO);
block(ls);
luaK_patchlist(fs, luaK_jump(fs), while_init);
luaK_patchtohere(fs, while_init); /* initial jump jumps to here */
luaK_moveexp(&v, fs->pc - while_init); /* correct pointers */
for (i=0; i<sizeexp; i++)
luaK_code(fs, codeexp[i], lineexp);
luaK_patchlist(fs, v.t, while_init+1);
luaK_patchtohere(fs, v.f);
check_match(ls, TK_END, TK_WHILE, line);
leaveblock(fs);