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First implementation of constant propagation

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Local constant variables initialized with compile-time constants
are optimized away from the code.
This commit is contained in:
Roberto Ierusalimschy
2019-07-12 11:38:42 -03:00
parent be8445d7e4
commit f6aab3ec1f
12 changed files with 249 additions and 119 deletions
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56
lcode.c
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@@ -67,6 +67,30 @@ static int tonumeral (const expdesc *e, TValue *v) {
}
/*
** If expression is a constant, fills 'v' with its value
** and returns 1. Otherwise, returns 0.
*/
int luaK_exp2const (FuncState *fs, const expdesc *e, TValue *v) {
if (hasjumps(e))
return 0; /* not a constant */
switch (e->k) {
case VFALSE: case VTRUE:
setbvalue(v, e->k == VTRUE);
return 1;
case VNIL:
setnilvalue(v);
return 1;
case VK: {
TValue *k = &fs->f->k[e->u.info];
setobj(fs->ls->L, v, k);
return 1;
}
default: return tonumeral(e, v);
}
}
/*
** Return the previous instruction of the current code. If there
** may be a jump target between the current instruction and the
@@ -629,6 +653,31 @@ static void luaK_float (FuncState *fs, int reg, lua_Number f) {
}
/*
** Convert a constant in 'v' into an expression description 'e'
*/
static void const2exp (FuncState *fs, TValue *v, expdesc *e) {
switch (ttypetag(v)) {
case LUA_TNUMINT:
e->k = VKINT; e->u.ival = ivalue(v);
break;
case LUA_TNUMFLT:
e->k = VKFLT; e->u.nval = fltvalue(v);
break;
case LUA_TBOOLEAN:
e->k = bvalue(v) ? VTRUE : VFALSE;
break;
case LUA_TNIL:
e->k = VNIL;
break;
case LUA_TSHRSTR: case LUA_TLNGSTR:
e->k = VK; e->u.info = luaK_stringK(fs, tsvalue(v));
break;
default: lua_assert(0);
}
}
/*
** Fix an expression to return the number of results 'nresults'.
** Either 'e' is a multi-ret expression (function call or vararg)
@@ -677,6 +726,11 @@ void luaK_setoneret (FuncState *fs, expdesc *e) {
*/
void luaK_dischargevars (FuncState *fs, expdesc *e) {
switch (e->k) {
case VCONST: {
TValue *val = &fs->ls->dyd->actvar.arr[e->u.info].k;
const2exp(fs, val, e);
break;
}
case VLOCAL: { /* already in a register */
e->u.info = e->u.var.sidx;
e->k = VNONRELOC; /* becomes a non-relocatable value */
@@ -1074,7 +1128,6 @@ void luaK_goiffalse (FuncState *fs, expdesc *e) {
** Code 'not e', doing constant folding.
*/
static void codenot (FuncState *fs, expdesc *e) {
luaK_dischargevars(fs, e);
switch (e->k) {
case VNIL: case VFALSE: {
e->k = VTRUE; /* true == not nil == not false */
@@ -1447,6 +1500,7 @@ static void codeeq (FuncState *fs, BinOpr opr, expdesc *e1, expdesc *e2) {
*/
void luaK_prefix (FuncState *fs, UnOpr op, expdesc *e, int line) {
static const expdesc ef = {VKINT, {0}, NO_JUMP, NO_JUMP};
luaK_dischargevars(fs, e);
switch (op) {
case OPR_MINUS: case OPR_BNOT: /* use 'ef' as fake 2nd operand */
if (constfolding(fs, op + LUA_OPUNM, e, &ef))