scc

commit ced6abe311cb8e3d553409e861f16fb7d64652cf
parent 2d870333e1b1f5383fe75996469bab34bf3aa97d
Author: Roberto E. Vargas Caballero <k0ga@shike2.com>
Date:   Wed,  3 Nov 2021 05:43:59 +0100

cc2/qbe: Use sethi number to drive assign generation

Sethi numbers gives an indication of the number of registers
needed to implement a tree, and generating first the subtree
with an higher sethi number improves the performance of  the
generated code.

Diffstat:
M
src/cmd/cc/cc2/target/qbe/cgen.c
 | 
11
++++++++---

1 file changed, 8 insertions(+), 3 deletions(-)
diff --git a/src/cmd/cc/cc2/target/qbe/cgen.c b/src/cmd/cc/cc2/target/qbe/cgen.c
@@ -585,9 +585,14 @@ rhs(Node *np, Node *ret)
 				l = l->left;
 			}
 		case 0:
-			/* TODO: see what is the most difficult */
-			lhs(l, &aux2);
-			rhs(r, ret);
+			if (l->complex >= r->complex) {
+				lhs(l, &aux2);
+				rhs(r, ret);
+			} else {
+				rhs(r, ret);
+				lhs(l, &aux2);
+			}
+
 			return assign(tp, &aux2, ret);
 		}
 		return ret;