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Improve alias analysis: disambiguate new allocations.

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This commit is contained in:
Mike Pall 2010-09-21 01:31:04 +02:00
parent 52b922c1e9
commit 23b5c56d41
1 changed files with 54 additions and 26 deletions
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50
src/lj_opt_mem.c
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@ -37,38 +37,64 @@ typedef enum {
/* -- ALOAD/HLOAD forwarding and ASTORE/HSTORE elimination ---------------- */
/* Alias analysis for two different table references. */
static AliasRet aa_table(jit_State *J, IRRef ta, IRRef tb)
{
IRIns *ir, *taba = IR(ta), *tabb = IR(tb);
int newa, newb;
lua_assert(ta != tb);
/* Disambiguate new allocations. */
newa = (taba->o == IR_TNEW || taba->o == IR_TDUP);
newb = (tabb->o == IR_TNEW || tabb->o == IR_TDUP);
if (newa && newb)
return ALIAS_NO; /* Two different allocations never alias. */
if (newb) { /* At least one allocation? */
IRRef tmp = ta; ta = tb; tb = tmp;
} else if (!newa) {
return ALIAS_MAY; /* Anything else: we just don't know. */
}
/* Now ta holds the allocation, tb the other table reference.
** The allocation might be stored and reloaded as tb. So perform a
** simplified escape analysis: check for intervening stores which have
** the allocation as the right operand.
*/
for (ir = IR(ta+1); ir < IR(tb); ir++)
if (ir->op2 == ta &&
(ir->o == IR_ASTORE || ir->o == IR_HSTORE ||
ir->o == IR_USTORE || ir->o == IR_FSTORE))
return ALIAS_MAY; /* Allocation was stored and might alias. */
return ALIAS_NO; /* Allocation doesn't alias the other reference. */
}
/* Alias analysis for array and hash access using key-based disambiguation. */
static AliasRet aa_ahref(jit_State *J, IRIns *refa, IRIns *refb)
{
IRRef ka = refa->op2;
IRRef kb = refb->op2;
IRIns *keya, *keyb;
IRRef ta, tb;
if (refa == refb)
return ALIAS_MUST; /* Shortcut for same refs. */
keya = IR(ka);
if (keya->o == IR_KSLOT) { ka = keya->op1; keya = IR(ka); }
keyb = IR(kb);
if (keyb->o == IR_KSLOT) { kb = keyb->op1; keyb = IR(kb); }
ta = (refa->o==IR_HREFK || refa->o==IR_AREF) ? IR(refa->op1)->op1 : refa->op1;
tb = (refb->o==IR_HREFK || refb->o==IR_AREF) ? IR(refb->op1)->op1 : refb->op1;
if (ka == kb) {
/* Same key. Check for same table with different ref (NEWREF vs. HREF). */
IRIns *ta = refa;
IRIns *tb = refb;
if (ta->o == IR_HREFK || ta->o == IR_AREF) ta = IR(ta->op1);
if (tb->o == IR_HREFK || tb->o == IR_AREF) tb = IR(tb->op1);
if (ta->op1 == tb->op1)
if (ta == tb)
return ALIAS_MUST; /* Same key, same table. */
else
return ALIAS_MAY; /* Same key, possibly different table. */
return aa_table(J, ta, tb); /* Same key, possibly different table. */
}
if (irref_isk(ka) && irref_isk(kb))
return ALIAS_NO; /* Different constant keys. */
if (refa->o == IR_AREF) {
/* Disambiguate array references based on index arithmetic. */
lua_assert(refb->o == IR_AREF);
if (refa->op1 == refb->op1) {
/* Same table, different non-const array keys. */
int32_t ofsa = 0, ofsb = 0;
IRRef basea = ka, baseb = kb;
lua_assert(refb->o == IR_AREF);
/* Gather base and offset from t[base] or t[base+-ofs]. */
if (keya->o == IR_ADD && irref_isk(keya->op2)) {
basea = keya->op1;
@ -84,7 +110,6 @@ static AliasRet aa_ahref(jit_State *J, IRIns *refa, IRIns *refb)
}
if (basea == baseb && ofsa != ofsb)
return ALIAS_NO; /* t[base+-o1] vs. t[base+-o2] and o1 != o2. */
}
} else {
/* Disambiguate hash references based on the type of their keys. */
lua_assert((refa->o==IR_HREF || refa->o==IR_HREFK || refa->o==IR_NEWREF) &&
@ -92,7 +117,10 @@ static AliasRet aa_ahref(jit_State *J, IRIns *refa, IRIns *refb)
if (!irt_sametype(keya->t, keyb->t))
return ALIAS_NO; /* Different key types. */
}
return ALIAS_MAY; /* Anything else: we just don't know. */
if (ta == tb)
return ALIAS_MAY; /* Same table, cannot disambiguate keys. */
else
return aa_table(J, ta, tb); /* Try to disambiguate tables. */
}
/* Array and hash load forwarding. */