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.

llvm-svn: 163335

llvm/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

llvm/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;
@@ -749,6 +766,31 @@ void LiveIntervals::addKillFlags() {
       MachineInstr *MI = getInstructionFromIndex(RI->end);
       if (!MI)
         continue;
+
+      // 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);
     }
   }

llvm/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();