Try again to teach getFirstTerminator() about debug values.

Fix some callers to better deal with debug values.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@123419 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/MachineBasicBlock.cpp

@@ -155,11 +155,22 @@ MachineBasicBlock::SkipPHIsAndLabels(MachineBasicBlock::iterator I) {
 }
 
 MachineBasicBlock::iterator MachineBasicBlock::getFirstTerminator() {
-  iterator I = end();
-  while (I != begin() && (--I)->getDesc().isTerminator())
-    ; /*noop */
-  if (I != end() && !I->getDesc().isTerminator()) ++I;
-  return I;
+  iterator B = begin(), I = end();
+  iterator Term = I;
+  while (I != B) {
+    --I;
+    // Ignore any debug values after the first terminator.
+    if (I->isDebugValue())
+      continue;
+    // Stop once we see a non-debug non-terminator.
+    if (!I->getDesc().isTerminator())
+      break;
+    // Earliest terminator so far.
+    Term = I;
+  }
+  // Return the first terminator, or end().
+  // Everything after Term is terminators and debug values.
+  return Term;
 }
 
 MachineBasicBlock::iterator MachineBasicBlock::getLastNonDebugInstr() {

lib/CodeGen/PHIElimination.cpp

@@ -339,6 +339,8 @@ void PHIElimination::LowerAtomicPHINode(
 #ifndef NDEBUG
         for (MachineBasicBlock::iterator TI = llvm::next(Term);
              TI != opBlock.end(); ++TI) {
+          if (TI->isDebugValue())
+            continue;
           assert(!TI->readsRegister(SrcReg) &&
                  "Terminator instructions cannot use virtual registers unless"
                  "they are the first terminator in a block!");
@@ -347,9 +349,13 @@ void PHIElimination::LowerAtomicPHINode(
       } else if (reusedIncoming || !IncomingReg) {
         // We may have to rewind a bit if we didn't insert a copy this time.
         KillInst = Term;
-        while (KillInst != opBlock.begin())
-          if ((--KillInst)->readsRegister(SrcReg))
+        while (KillInst != opBlock.begin()) {
+          --KillInst;
+          if (KillInst->isDebugValue())
+            continue;
+          if (KillInst->readsRegister(SrcReg))
             break;
+        }
       } else {
         // We just inserted this copy.
         KillInst = prior(InsertPos);