From 4a5c9a1ac521f206b940aca5ab9d06a9db0c1445 Mon Sep 17 00:00:00 2001
From: Matthew Fernandez <matthew.fernandez@gmail.com>
Date: Sat, 12 Jun 2021 12:36:31 -0700
Subject: [PATCH] return a value instead of pointer from Blocks::totalOrder

This function dynamically allocated a list and returned a pointer to this,
presumably under the assumption that copying this kind of object during return
is expensive. However, Named Return Value Optimization (NRVO) applies to this
function. So the compiler can elide the copy during return, making a value
cheaper than a heap pointer here.
---
 lib/vpsc/blocks.cpp     | 6 +++---
 lib/vpsc/blocks.h       | 2 +-
 lib/vpsc/solve_VPSC.cpp | 5 ++---
 3 files changed, 6 insertions(+), 7 deletions(-)

diff --git a/lib/vpsc/blocks.cpp b/lib/vpsc/blocks.cpp
index f8b09e5cc..e6f99bfa4 100644
--- a/lib/vpsc/blocks.cpp
+++ b/lib/vpsc/blocks.cpp
@@ -54,14 +54,14 @@ Blocks::~Blocks()
  * returns a list of variables with total ordering determined by the constraint 
  * DAG
  */
-list<Variable*> *Blocks::totalOrder() {
-	list<Variable*> *order = new list<Variable*>;
+list<Variable*> Blocks::totalOrder() {
+	list<Variable*> order;
 	for(int i=0;i<nvs;i++) {
 		vs[i]->visited=false;
 	}
 	for(int i=0;i<nvs;i++) {
 		if(vs[i]->in.empty()) {
-			dfsVisit(vs[i],*order);
+			dfsVisit(vs[i],order);
 		}
 	}
 	return order;
diff --git a/lib/vpsc/blocks.h b/lib/vpsc/blocks.h
index b5b544236..e39ce81ae 100644
--- a/lib/vpsc/blocks.h
+++ b/lib/vpsc/blocks.h
@@ -42,7 +42,7 @@ public:
 	void mergeLeft(Block *r);
 	void mergeRight(Block *l);
 	void split(Block *b, Block *&l, Block *&r, Constraint *c);
-	std::list<Variable*> *totalOrder();
+	std::list<Variable*> totalOrder();
 	void cleanup();
 	double cost();
 private:
diff --git a/lib/vpsc/solve_VPSC.cpp b/lib/vpsc/solve_VPSC.cpp
index 10bf69e03..c1ea8c3ea 100644
--- a/lib/vpsc/solve_VPSC.cpp
+++ b/lib/vpsc/solve_VPSC.cpp
@@ -74,8 +74,8 @@ void VPSC::printBlocks() {
 * another so that constraints internal to the block are satisfied.
 */
 void VPSC::satisfy() {
-	list<Variable*> *vs=bs.totalOrder();
-	for(Variable *v : *vs) {
+	list<Variable*> vs=bs.totalOrder();
+	for(Variable *v : vs) {
 		if(!v->block->deleted) {
 			bs.mergeLeft(v->block);
 		}
@@ -91,7 +91,6 @@ void VPSC::satisfy() {
 			throw "Unsatisfied constraint";
 		}
 	}
-	delete vs;
 }
 
 void VPSC::refine() {
-- 
2.40.0