Subzero : Live Range Splitting after initial Register Allocation

src/IceOperand.cpp

Index: src/IceOperand.cpp
diff --git a/src/IceOperand.cpp b/src/IceOperand.cpp
index 540252b64785faa14f8ffecdbc8ef4689f75cea0..870e7fbaada65f76fe596165d919036b732cc571 100644
--- a/src/IceOperand.cpp
+++ b/src/IceOperand.cpp
@@ -101,15 +101,21 @@ bool operator==(const RegWeight &A, const RegWeight &B) {
   return !(B < A) && !(A < B);
 }
 
-void LiveRange::addSegment(InstNumberT Start, InstNumberT End) {
-  if (!Range.empty()) {
-    // Check for merge opportunity.
-    InstNumberT CurrentEnd = Range.back().second;
-    assert(Start >= CurrentEnd);
-    if (Start == CurrentEnd) {
-      Range.back().second = End;
-      return;
+void LiveRange::addSegment(InstNumberT Start, InstNumberT End, CfgNode *Node) {
+  if (!getFlags().getGlobalSplitting()) {

[Jim Stichnoth, 2016/07/29 17:04:06]

Remove the '!' and reverse the if/then/else branches.

[manasijm, 2016/08/01 22:20:03]

Done.

+    if (!Range.empty()) {
+      // Check for merge opportunity.
+      InstNumberT CurrentEnd = Range.back().second;
+      assert(Start >= CurrentEnd);
+      if (Start == CurrentEnd) {
+        Range.back().second = End;
+        return;
+      }
     }
+  } else {
+    // Disable merging to make sure a live range 'segment' has a single node.

[Jim Stichnoth, 2016/07/29 17:04:06]

I think you could still merge if the node is the same?  But I don't think that
would ever actually happen in today's code.  Maybe note this in a comment?  e.g.
"Merging could be allowed if the nodes are the same, but this currently never
happens in practice."

[manasijm, 2016/08/01 22:20:03]

Done.

+    assert(NodeMap.find(Start) == NodeMap.end());
+    NodeMap[Start] = Node;
   }
   Range.push_back(RangeElementType(Start, End));
 }