From e617ccb80da76821379bbff4a2fdcd09e8401e8b Mon Sep 17 00:00:00 2001
From: Jakob Stoklund Olesen <stoklund@2pi.dk>
Date: Thu, 6 Sep 2012 18:15:18 +0000
Subject: [PATCH] Handle overlapping regunit intervals in
 LiveIntervals::addKillFlags().

We will soon allow virtual register live ranges to overlap regunit live
ranges when the physreg is defined as a copy of the virtreg:

  %EAX = COPY %vreg5
  FOO %vreg5
  BAR %EAX<kill>

There is no real interference since %vreg5 and %EAX have the same value
where they overlap.

This patch prevents addKillFlags from adding virtreg kill flags to FOO
where the assigned physreg is overlapping the virtual register live
range.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@163335 91177308-0d34-0410-b5e6-96231b3b80d8
---
 include/llvm/CodeGen/LiveIntervalAnalysis.h |  2 +-
 lib/CodeGen/LiveIntervalAnalysis.cpp        | 46 ++++++++++++++++++++-
 lib/CodeGen/VirtRegMap.cpp                  |  2 +-
 3 files changed, 46 insertions(+), 4 deletions(-)

diff --git a/include/llvm/CodeGen/LiveIntervalAnalysis.h b/include/llvm/CodeGen/LiveIntervalAnalysis.h
index da521dbc535..bf7469093a8 100644
--- a/include/llvm/CodeGen/LiveIntervalAnalysis.h
+++ b/include/llvm/CodeGen/LiveIntervalAnalysis.h
@@ -252,7 +252,7 @@ namespace llvm {
 
     /// addKillFlags - Add kill flags to any instruction that kills a virtual
     /// register.
-    void addKillFlags();
+    void addKillFlags(const VirtRegMap*);
 
     /// handleMove - call this method to notify LiveIntervals that
     /// instruction 'mi' has been moved within a basic block. This will update
diff --git a/lib/CodeGen/LiveIntervalAnalysis.cpp b/lib/CodeGen/LiveIntervalAnalysis.cpp
index bdf4f2dfffc..b447c3c2d70 100644
--- a/lib/CodeGen/LiveIntervalAnalysis.cpp
+++ b/lib/CodeGen/LiveIntervalAnalysis.cpp
@@ -34,6 +34,7 @@
 #include "llvm/ADT/DenseSet.h"
 #include "llvm/ADT/STLExtras.h"
 #include "LiveRangeCalc.h"
+#include "VirtRegMap.h"
 #include <algorithm>
 #include <limits>
 #include <cmath>
@@ -733,12 +734,28 @@ bool LiveIntervals::shrinkToUses(LiveInterval *li,
 // Register allocator hooks.
 //
 
-void LiveIntervals::addKillFlags() {
+void LiveIntervals::addKillFlags(const VirtRegMap *VRM) {
+  // Keep track of regunit ranges.
+  SmallVector<std::pair<LiveInterval*, LiveInterval::iterator>, 8> RU;
+
   for (unsigned i = 0, e = MRI->getNumVirtRegs(); i != e; ++i) {
     unsigned Reg = TargetRegisterInfo::index2VirtReg(i);
     if (MRI->reg_nodbg_empty(Reg))
       continue;
     LiveInterval *LI = &getInterval(Reg);
+    if (LI->empty())
+      continue;
+
+    // Find the regunit intervals for the assigned register. They may overlap
+    // the virtual register live range, cancelling any kills.
+    RU.clear();
+    for (MCRegUnitIterator Units(VRM->getPhys(Reg), TRI); Units.isValid();
+         ++Units) {
+      LiveInterval *RUInt = &getRegUnit(*Units);
+      if (RUInt->empty())
+        continue;
+      RU.push_back(std::make_pair(RUInt, RUInt->find(LI->begin()->end)));
+    }
 
     // Every instruction that kills Reg corresponds to a live range end point.
     for (LiveInterval::iterator RI = LI->begin(), RE = LI->end(); RI != RE;
@@ -749,7 +766,32 @@ void LiveIntervals::addKillFlags() {
       MachineInstr *MI = getInstructionFromIndex(RI->end);
       if (!MI)
         continue;
-      MI->addRegisterKilled(Reg, NULL);
+
+      // Check if any of the reguints are live beyond the end of RI. That could
+      // happen when a physreg is defined as a copy of a virtreg:
+      //
+      //   %EAX = COPY %vreg5
+      //   FOO %vreg5         <--- MI, cancel kill because %EAX is live.
+      //   BAR %EAX<kill>
+      //
+      // There should be no kill flag on FOO when %vreg5 is rewritten as %EAX.
+      bool CancelKill = false;
+      for (unsigned u = 0, e = RU.size(); u != e; ++u) {
+        LiveInterval *RInt = RU[u].first;
+        LiveInterval::iterator &I = RU[u].second;
+        if (I == RInt->end())
+          continue;
+        I = RInt->advanceTo(I, RI->end);
+        if (I == RInt->end() || I->start >= RI->end)
+          continue;
+        // I is overlapping RI.
+        CancelKill = true;
+        break;
+      }
+      if (CancelKill)
+        MI->clearRegisterKills(Reg, NULL);
+      else
+        MI->addRegisterKilled(Reg, NULL);
     }
   }
 }
diff --git a/lib/CodeGen/VirtRegMap.cpp b/lib/CodeGen/VirtRegMap.cpp
index a1cac7c5b2a..6343e8a3529 100644
--- a/lib/CodeGen/VirtRegMap.cpp
+++ b/lib/CodeGen/VirtRegMap.cpp
@@ -200,7 +200,7 @@ bool VirtRegRewriter::runOnMachineFunction(MachineFunction &fn) {
   DEBUG(VRM->dump());
 
   // Add kill flags while we still have virtual registers.
-  LIS->addKillFlags();
+  LIS->addKillFlags(VRM);
 
   // Live-in lists on basic blocks are required for physregs.
   addMBBLiveIns();