From 4637dd8bc093db5336f2bc1fc76e334969f2fa5c Mon Sep 17 00:00:00 2001
From: Fei Gao <fei.gao@arm.com>
Date: Thu, 23 Nov 2023 06:38:57 +0000
Subject: [PATCH] Fix comments from aph

---
 src/hotspot/share/opto/output.cpp | 21 ++++++++++-----------
 1 file changed, 10 insertions(+), 11 deletions(-)

diff --git a/src/hotspot/share/opto/output.cpp b/src/hotspot/share/opto/output.cpp
index dc7ec7a305a46..64d98f27ff614 100644
--- a/src/hotspot/share/opto/output.cpp
+++ b/src/hotspot/share/opto/output.cpp
@@ -169,11 +169,10 @@ class Scheduling {
   // Add a node to the current bundle
   void AddNodeToBundle(Node *n, const Block *bb);
 
-  // Return true only when the stack offset of the first spill node is
-  // greater than the stack offset of the second one. Otherwise, return false.
-  // When compare_two_spill_nodes(first, second) returns true, we think that
-  // "second" should be scheduled before "first" in the final basic block.
-  bool compare_two_spill_nodes(Node* first, Node* second);
+  // Return an integer less than, equal to, or greater than zero
+  // if the stack offset of the first argument is respectively
+  // less than, equal to, or greater than the second.
+  int compare_two_spill_nodes(Node* first, Node* second);
 
   // Add a node to the list of available nodes
   void AddNodeToAvailableList(Node *n);
@@ -2277,7 +2276,7 @@ Node * Scheduling::ChooseNodeToBundle() {
   return _available[0];
 }
 
-bool Scheduling::compare_two_spill_nodes(Node* first, Node* second) {
+int Scheduling::compare_two_spill_nodes(Node* first, Node* second) {
   assert(first->is_MachSpillCopy() && second->is_MachSpillCopy(), "");
 
   OptoReg::Name first_src_lo = _regalloc->get_reg_first(first->in(1));
@@ -2288,16 +2287,16 @@ bool Scheduling::compare_two_spill_nodes(Node* first, Node* second) {
   // Comparison between stack -> reg and stack -> reg
   if (OptoReg::is_stack(first_src_lo) && OptoReg::is_stack(second_src_lo) &&
       OptoReg::is_reg(first_dst_lo) && OptoReg::is_reg(second_dst_lo)) {
-    return _regalloc->reg2offset(first_src_lo) > _regalloc->reg2offset(second_src_lo);
+    return _regalloc->reg2offset(first_src_lo) - _regalloc->reg2offset(second_src_lo);
   }
 
   // Comparison between reg -> stack and reg -> stack
   if (OptoReg::is_stack(first_dst_lo) && OptoReg::is_stack(second_dst_lo) &&
       OptoReg::is_reg(first_src_lo) && OptoReg::is_reg(second_src_lo)) {
-    return _regalloc->reg2offset(first_dst_lo) > _regalloc->reg2offset(second_dst_lo);
+    return _regalloc->reg2offset(first_dst_lo) - _regalloc->reg2offset(second_dst_lo);
   }
 
-  return false;
+  return 0; // Not comparable
 }
 
 void Scheduling::AddNodeToAvailableList(Node *n) {
@@ -2313,7 +2312,7 @@ void Scheduling::AddNodeToAvailableList(Node *n) {
 
   // Insert in latency order (insertion sort). If two MachSpillCopyNodes
   // for stack spilling or unspilling have the same latency, we sort
-  // them in the order of stack offset. Some backends (aarch64) may also
+  // them in the order of stack offset. Some ports (e.g. aarch64) may also
   // have more opportunities to do ld/st merging
   uint i;
   for (i = 0; i < _available.size(); i++) {
@@ -2321,7 +2320,7 @@ void Scheduling::AddNodeToAvailableList(Node *n) {
       break;
     } else if (_current_latency[_available[i]->_idx] == latency &&
                n->is_MachSpillCopy() && _available[i]->is_MachSpillCopy() &&
-               compare_two_spill_nodes(n, _available[i])) {
+               compare_two_spill_nodes(n, _available[i]) > 0) {
       break;
     }
   }