From f2f0589b02601184047ad5eb729ed3efd2b6a9c1 Mon Sep 17 00:00:00 2001
From: Matthias Braun <matze@braunis.de>
Date: Wed, 10 Dec 2014 01:12:40 +0000
Subject: [PATCH] LiveInterval: Add removeEmptySubRanges().

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@223887 91177308-0d34-0410-b5e6-96231b3b80d8
---
 include/llvm/CodeGen/LiveInterval.h |  4 ++++
 lib/CodeGen/LiveInterval.cpp        | 17 +++++++++++++++++
 2 files changed, 21 insertions(+)

diff --git a/include/llvm/CodeGen/LiveInterval.h b/include/llvm/CodeGen/LiveInterval.h
index 18700801ea2..0eead2c84bf 100644
--- a/include/llvm/CodeGen/LiveInterval.h
+++ b/include/llvm/CodeGen/LiveInterval.h
@@ -669,6 +669,10 @@ namespace llvm {
       SubRanges = nullptr;
     }
 
+    /// Removes all subranges without any segments (subranges without segments
+    /// are not considered valid and should only exist temporarily).
+    void removeEmptySubRanges();
+
     /// getSize - Returns the sum of sizes of all the LiveRange's.
     ///
     unsigned getSize() const;
diff --git a/lib/CodeGen/LiveInterval.cpp b/lib/CodeGen/LiveInterval.cpp
index 5162579adf1..5d1b99400b7 100644
--- a/lib/CodeGen/LiveInterval.cpp
+++ b/lib/CodeGen/LiveInterval.cpp
@@ -592,6 +592,23 @@ VNInfo *LiveRange::MergeValueNumberInto(VNInfo *V1, VNInfo *V2) {
   return V2;
 }
 
+void LiveInterval::removeEmptySubRanges() {
+  SubRange **NextPtr = &SubRanges;
+  SubRange *I = *NextPtr;
+  while (I != nullptr) {
+    if (!I->empty()) {
+      NextPtr = &I->Next;
+      I = *NextPtr;
+      continue;
+    }
+    // Skip empty subranges until we find the first nonempty one.
+    do {
+      I = I->Next;
+    } while (I != nullptr && I->empty());
+    *NextPtr = I;
+  }
+}
+
 unsigned LiveInterval::getSize() const {
   unsigned Sum = 0;
   for (const_iterator I = begin(), E = end(); I != E; ++I)