Fix a problem that occurs when PHI nodes have multiple entries for the same predecessor

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@5055 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/RegAllocSimple.cpp

@@ -290,11 +290,27 @@ void RegAllocSimple::EliminatePHINodes(MachineBasicBlock &MBB) {
       // Get the MachineBasicBlock equivalent of the BasicBlock that is the
       // source path the phi
       MachineBasicBlock &opBlock = *MI->getOperand(i).getMachineBasicBlock();
+
+      // Check to make sure we haven't already emitted the copy for this block.
+      // This can happen because PHI nodes may have multiple entries for the
+      // same basic block.  It doesn't matter which entry we use though, because
+      // all incoming values are guaranteed to be the same for a particular bb.
+      //
+      // Note that this is N^2 in the number of phi node entries, but since the
+      // # of entries is tiny, this is not a problem.
+      //
+      bool HaveNotEmitted = true;
+      for (int op = MI->getNumOperands() - 1; op != i; op -= 2)
+        if (&opBlock == MI->getOperand(op).getMachineBasicBlock()) {
+          HaveNotEmitted = false;
+          break;
+        }
+
+      if (HaveNotEmitted) {
         MachineBasicBlock::iterator opI = opBlock.end();
         MachineInstr *opMI = *--opI;
         
-      // must backtrack over ALL the branches in the previous block, until no
+        // must backtrack over ALL the branches in the previous block
-      // more
         while (MII.isBranch(opMI->getOpcode()) && opI != opBlock.begin())
           opMI = *--opI;
         
@@ -319,6 +335,7 @@ void RegAllocSimple::EliminatePHINodes(MachineBasicBlock &MBB) {
           // Save that register value to the stack of the TARGET REG
           saveVirtRegToStack(opBlock, opI, virtualReg, physReg);
         }
+      }
 
       // make regs available to other instructions
       clearAllRegs();