Handle DBG_VALUE mixed with labels when doing PHI

elimination.  Before a DBG_VALUE could affect codegen.
The solution here is imperfect and not final.

llvm-svn: 96318

lib/CodeGen/PHIElimination.h

@@ -109,12 +109,29 @@ namespace llvm {
     // SkipPHIsAndLabels - Copies need to be inserted after phi nodes and
     // also after any exception handling labels: in landing pads execution
     // starts at the label, so any copies placed before it won't be executed!
+    // We also deal with DBG_VALUEs, which are a bit tricky:
+    //  PHI
+    //  DBG_VALUE
+    //  LABEL
+    // Here the DBG_VALUE needs to be skipped, and if it refers to a PHI it
+    // needs to be annulled or, better, moved to follow the label, as well.
+    //  PHI
+    //  DBG_VALUE
+    //  no label
+    // Here it is not a good idea to skip the DBG_VALUE.
+    // FIXME: For now we skip and annul all DBG_VALUEs, maximally simple and
+    // maximally stupid.
     MachineBasicBlock::iterator SkipPHIsAndLabels(MachineBasicBlock &MBB,
                                                 MachineBasicBlock::iterator I) {
       // Rather than assuming that EH labels come before other kinds of labels,
       // just skip all labels.
-      while (I != MBB.end() && (I->isPHI() || I->isLabel()))
+      while (I != MBB.end() && 
+             (I->isPHI() || I->isLabel() || I->isDebugValue())) {
+        if (I->isDebugValue() && I->getNumOperands()==3 && 
+            I->getOperand(0).isReg())
+          I->getOperand(0).setReg(0U);
         ++I;
+      }
       return I;
     }