Fix a bug where we incorrectly value numbered the first PHI definition the

same as the PHI use.  This is not correct as the PHI use value is different
depending on which branch is taken.  This fixes espresso with aggressive
coallescing, and perhaps others.

llvm-svn: 15189

1 files changed, 26 insertions, 3 deletions

diff --git a/llvm/lib/CodeGen/LiveIntervalAnalysis.cpp b/llvm/lib/CodeGen/LiveIntervalAnalysis.cpp
index d54eaefb660..361210e1062 100644
--- a/llvm/lib/CodeGen/LiveIntervalAnalysis.cpp
+++ b/llvm/lib/CodeGen/LiveIntervalAnalysis.cpp
@@ -393,9 +393,32 @@ void LiveIntervals::handleVirtualRegisterDef(MachineBasicBlock* mbb,
          DEBUG(std::cerr << "RESULT: " << interval);
 
        } else {
-         // Otherwise, this must be because of phi elimination.  In this case, 
-         // the defined value will be live until the end of the basic block it
-         // is defined in.
+         // Otherwise, this must be because of phi elimination.  If this is the
+         // first redefinition of the vreg that we have seen, go back and change
+         // the live range in the PHI block to be a different value number.
+         if (interval.containsOneValue()) {
+           assert(vi.Kills.size() == 1 &&
+                  "PHI elimination vreg should have one kill, the PHI itself!");
+
+           // Remove the old range that we now know has an incorrect number.
+           MachineInstr *Killer = vi.Kills[0];
+           unsigned Start = getInstructionIndex(Killer->getParent()->begin());
+           unsigned End = getUseIndex(getInstructionIndex(Killer))+1;
+           DEBUG(std::cerr << "Removing [" << Start << "," << End << "] from: "
+                 << interval << "\n");
+           interval.removeRange(Start, End);
+           DEBUG(std::cerr << "RESULT: " << interval);
+
+           // Replace the interval with one of a NEW value number.
+           LiveRange LR(Start, End, interval.getNextValue());
+           DEBUG(std::cerr << " replace range with " << LR);
+           interval.addRange(LR);
+           DEBUG(std::cerr << "RESULT: " << interval);
+         }
+
+         // In the case of PHI elimination, each variable definition is only
+         // live until the end of the block.  We've already taken care of the
+         // rest of the live range.
          unsigned defIndex = getDefIndex(getInstructionIndex(mi));
          LiveRange LR(defIndex, 
                       getInstructionIndex(&mbb->back()) + InstrSlots::NUM,