[hackers] [scc] Add more identities for logic operators || Roberto E. Vargas Caballero

From: <git_AT_suckless.org>
Date: Sat, 5 Sep 2015 19:59:17 +0200 (CEST)

commit 4343d4491f8251b0af5065d3898a2dc7cf8abf2f
Author: Roberto E. Vargas Caballero <k0ga_AT_shike2.com>
AuthorDate: Sat Sep 5 19:54:51 2015 +0200
Commit: Roberto E. Vargas Caballero <k0ga_AT_shike2.com>
CommitDate: Sat Sep 5 19:54:51 2015 +0200

    Add more identities for logic operators

diff --git a/cc1/fold.c b/cc1/fold.c
index fe6e7d9..bb4a16a 100644
--- a/cc1/fold.c
+++ b/cc1/fold.c
_AT_@ -376,83 +376,104 @@ ones(int n)
         return v;
 }
 
-/*
- * 0 || i => i
- * 1 || i => 1
- * 0 && i => 0
- * 1 && i => i
- * i >> 0 => i
- * i << 0 => i
- * i + 0 => i
- * i - 0 => i
- * i | 0 => i
- * i ^ 0 => i
- * i * 0 => i,0
- * i * 1 => i
- * i / 1 => i
- * i & ~0 => i
- * i % 1 => i,1
- */
 static Node *
 identity(int *op, Node *lp, Node *rp)
 {
- int iszero, isone, istrue, val;
+ int iszeror, isoner, istruer, val;
+ int iszerol, isonel, istruel;
 
         if (!rp)
                 return NULL;
 
- iszero = cmpnode(rp, 0);
- isone = cmpnode(rp, 1),
- istrue = !iszero && rp->constant;
+ iszeror = cmpnode(rp, 0);
+ isoner = cmpnode(rp, 1),
+ istruer = !iszeror && rp->constant;
+ iszerol = cmpnode(lp, 0);
+ isonel = cmpnode(lp, 1),
+ istruel = !iszerol && lp->constant;
 
         switch (*op) {
         case OOR:
- val = 1;
- goto logic_operator;
+ /*
+ * 1 || i => 1 (free right)
+ * i || 0 => i (free right)
+ * 0 || i => i (free left)
+ * i || 1 => i,1 (comma)
+ */
+ if (isonel | iszeror)
+ goto free_right;
+ if (iszerol)
+ goto free_left;
+ if (isoner)
+ goto change_to_comma;
+ return NULL;
         case OAND:
- val = 0;
- goto logic_operator;
+ /*
+ * 0 && i => 0 (free right)
+ * i && 1 => i (free right)
+ * 1 && i => i (free left)
+ * i && 0 => i,0 (comma)
+ */
+ if (iszerol | isoner)
+ goto free_right;
+ if (isonel)
+ goto free_left;
+ if (iszeror)
+ goto change_to_comma;
+ return NULL;
         case OSHL:
         case OSHR:
         case OBXOR:
         case OADD:
         case OBOR:
         case OSUB:
- if (iszero)
+ /*
+ * i >> 0 => i
+ * i << 0 => i
+ * i + 0 => i
+ * i - 0 => i
+ * i | 0 => i
+ * i ^ 0 => i
+ */
+ if (iszeror)
                         goto free_right;
                 return NULL;
         case OMUL:
- if (iszero)
+ /*
+ * i * 0 => i,0
+ * i * 1 => i
+ */
+ if (iszeror)
                         goto change_to_comma;
+ if (isoner)
+ goto free_right;
+ return NULL;
         case ODIV:
- if (isone)
+ /* i / 1 => i */
+ if (isoner)
                         goto free_right;
                 return NULL;
         case OBAND:
+ /* i & ~0 => i */
                 if (cmpnode(rp, ones(lp->type->size * 8)))
                         goto free_right;
                 return NULL;
         case OMOD:
- if (isone)
+ /* i % 1 => i,1 */
+ if (isoner)
                         goto change_to_comma;
         default:
                 return NULL;
         }
 
-logic_operator:
- if (!lp->constant)
- return NULL;
- if (cmpnode(lp, val))
- goto free_right;
+free_right:
+ freetree(rp);
+ return lp;
 
 free_left:
         freetree(lp);
         return rp;
 
-free_right:
- freetree(rp);
- return lp;
-
 change_to_comma:
         *op = OCOMMA;
         return NULL;
Received on Sat Sep 05 2015 - 19:59:17 CEST