[hackers] [scc] [cc2-qbe] Add Sethi-Ullman number calculation || Roberto E. Vargas Caballero

[git]

commit 53e82078e4f9c8450ba94ba169cce9b51d513df2
Author:     Roberto E. Vargas Caballero <roberto.var...@igrid-td.com>
AuthorDate: Tue Apr 12 17:16:50 2016 +0200
Commit:     Roberto E. Vargas Caballero <roberto.var...@igrid-td.com>
CommitDate: Tue Apr 12 17:16:50 2016 +0200

    [cc2-qbe] Add Sethi-Ullman number calculation
    
    In the case of QBE we can ignore the addressability, and we only
    use it for the Sethi-Ullman number generation

diff --git a/cc2/arch/qbe/cgen.c b/cc2/arch/qbe/cgen.c
index 54e3ed2..43236e1 100644
--- a/cc2/arch/qbe/cgen.c
+++ b/cc2/arch/qbe/cgen.c
@@ -7,7 +7,58 @@ generate(void)
 {
 }
 
+/*
+ * This is strongly influenced by
+ * http://plan9.bell-labs.com/sys/doc/compiler.ps (/sys/doc/compiler.ps)
+ * calculate addresability as follows
+ *     AUTO => 11          value+fp
+ *     REG => 11           reg
+ *     STATIC => 11        (value)
+ *     CONST => 11         $value
+ * These values of addressability are not used in the code generation.
+ * They are only used to calculate the Sethi-Ullman numbers. Since
+ * QBE is AMD64 targered we could do a better job here, and try to
+ * detect some of the complex addressing modes of these processors.
+ */
 Node *
 sethi(Node *np)
 {
+       Node *lp, *rp;
+
+       if (!np)
+               return np;
+
+       np->complex = 0;
+       np->address = 0;
+       lp = np->left;
+       rp = np->right;
+
+       switch (np->op) {
+       case AUTO:
+       case REG:
+       case MEM:
+       case CONST:
+               np->address = 11;
+               break;
+       default:
+               sethi(lp);
+               sethi(rp);
+               break;
+       }
+
+       if (np->address > 10)
+               return np;
+       if (lp)
+               rp->complex = lp->complex;
+       if (rp) {
+               int d = np->complex - rp->complex;
+
+               if (d == 0)
+                       ++np->complex;
+               else if (d < 0)
+                       np->complex = rp->complex;
+       }
+       if (np->complex == 0)
+               ++rp->complex;
+       return np;
 }
diff --git a/cc2/arch/z80/cgen.c b/cc2/arch/z80/cgen.c
index 567d209..95067f9 100644
--- a/cc2/arch/z80/cgen.c
+++ b/cc2/arch/z80/cgen.c
@@ -42,10 +42,8 @@ sethi(Node *np)
                np->address = 20;
                break;
        default:
-               if (lp)
-                       sethi(lp);
-               if (rp)
-                       sethi(rp);
+               sethi(lp);
+               sethi(rp);
                break;
        }