[hackers] [scc] Add algebraic identities simplifications || Roberto E. Vargas Caballero

From: <git_AT_suckless.org>
Date: Wed, 26 Aug 2015 22:32:48 +0200 (CEST)

commit cd9f71bbfc1f5bf8fc7a63931c29cce9acabda97
Author: Roberto E. Vargas Caballero <k0ga_AT_shike2.com>
AuthorDate: Wed Aug 26 21:44:06 2015 +0200
Commit: Roberto E. Vargas Caballero <k0ga_AT_shike2.com>
CommitDate: Wed Aug 26 21:44:06 2015 +0200

    Add algebraic identities simplifications
    
    These kind of expressions are common in array expressions, so this commit
    simmplify a lot the intermediate file, and makes easier to validate the
    regression tests.

diff --git a/cc1/expr.c b/cc1/expr.c
index 9ffa3a8..7414c00 100644
--- a/cc1/expr.c
+++ b/cc1/expr.c
_AT_@ -40,9 +40,19 @@ static Node *
 simplify(unsigned char op, Type *tp, Node *lp, Node *rp)
 {
         Symbol *sym, *ls, *rs, aux;
+ int iszero, isone, noconst = 0;
 
- if (!lp->constant || !rp->constant)
+ if (!lp->constant && !rp->constant)
                 goto no_simplify;
+ if (!rp->constant) {
+ Node *np;
+ np = lp;
+ lp = rp;
+ rp = np;
+ }
+ if (!lp->constant)
+ noconst = 1;
+
         ls = lp->sym, rs = rp->sym;
         aux.type = tp;
 
_AT_@ -62,71 +72,143 @@ simplify(unsigned char op, Type *tp, Node *lp, Node *rp)
         }
 
         switch (tp->op) {
+ case PTR:
         case INT:
         cmp_integers:
+ iszero = SYMICMP(rs, 0);
+ isone = SYMICMP(rs, 1);
                 switch (op) {
                 case OADD:
+ if (iszero)
+ return lp;
+ if (noconst)
+ goto no_simplify;
                         FOLDINT(&aux, ls, rs, +);
                         break;
                 case OSUB:
+ if (iszero)
+ return lp;
+ if (noconst)
+ goto no_simplify;
                         FOLDINT(&aux, ls, rs, -);
                         break;
                 case OMUL:
+ if (isone)
+ return lp;
+ if (iszero)
+ return constnode(zero);
+ if (noconst)
+ goto no_simplify;
                         FOLDINT(&aux, ls, rs, *);
                         break;
                 case ODIV:
- if (SYMICMP(&aux, 0))
+ if (isone)
+ return lp;
+ if (iszero)
                                 goto division_by_0;
+ if (noconst)
+ goto no_simplify;
                         FOLDINT(&aux, ls, rs, /);
                         break;
                 case OMOD:
- if (SYMICMP(&aux, 0))
+ if (iszero)
                                 goto division_by_0;
+ if (noconst)
+ goto no_simplify;
                         FOLDINT(&aux, ls, rs, %);
                         break;
                 case OSHL:
+ if (iszero)
+ return lp;
+ if (noconst)
+ goto no_simplify;
                         FOLDINT(&aux, ls, rs, <<);
                         break;
                 case OSHR:
+ if (iszero)
+ return lp;
+ if (noconst)
+ goto no_simplify;
                         FOLDINT(&aux, ls, rs, >>);
                         break;
                 case OBAND:
+ if (SYMICMP(rs, ~0))
+ return lp;
+ if (noconst)
+ goto no_simplify;
                         FOLDINT(&aux, ls, rs, &);
                         break;
                 case OBXOR:
+ if (iszero)
+ return lp;
+ if (noconst)
+ goto no_simplify;
                         FOLDINT(&aux, ls, rs, ^);
                         break;
                 case OBOR:
+ if (iszero)
+ return lp;
+ if (noconst)
+ goto no_simplify;
                         FOLDINT(&aux, ls, rs, |);
                         break;
                 case OAND:
+ if (!iszero)
+ return lp;
+ /* TODO: What happens with something like f(0) && 0? */
+ if (noconst)
+ goto no_simplify;
                         FOLDINT(&aux, ls, rs, &&);
                         break;
                 case OOR:
+ if (iszero)
+ return lp;
+ if (noconst)
+ goto no_simplify;
+ /* TODO: What happens with something like f(0) || 1? */
                         FOLDINT(&aux, ls, rs, ||);
                         break;
                 case OLT:
+ /* TODO: what happens with signess? */
+ if (noconst)
+ goto no_simplify;
                         aux.u.i = CMPISYM(&aux, ls, rs, <);
                         break;
                 case OGT:
+ /* TODO: what happens with signess? */
+ if (noconst)
+ goto no_simplify;
                         aux.u.i = CMPISYM(&aux, ls, rs, >);
                         break;
                 case OGE:
+ /* TODO: what happens with signess? */
+ if (noconst)
+ goto no_simplify;
                         aux.u.i = CMPISYM(&aux, ls, rs, >=);
                         break;
                 case OLE:
+ /* TODO: what happens with signess? */
+ if (noconst)
+ goto no_simplify;
                         aux.u.i = CMPISYM(&aux, ls, rs, <=);
                         break;
                 case OEQ:
+ /* TODO: what happens with signess? */
+ if (noconst)
+ goto no_simplify;
                         aux.u.i = CMPISYM(&aux, ls, rs, ==);
                         break;
                 case ONE:
+ /* TODO: what happens with signess? */
+ if (noconst)
+ goto no_simplify;
                         aux.u.i = CMPISYM(&aux, ls, rs, !=);
                         break;
                 }
                 break;
         case FLOAT:
         cmp_floats:
+ /* TODO: Add algebraic reductions for floats */
                 switch (op) {
                 case OADD:
                         aux.u.f = ls->u.f + rs->u.f;
Received on Wed Aug 26 2015 - 22:32:48 CEST