Teach MachineBasicBlock::getFirstTerminator to ignore debug values.

It will still return an iterator that points to the first terminator or end(),
but there may be DBG_VALUE instructions following the first terminator.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@123384 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 18 insertions, 5 deletions

diff --git a/lib/CodeGen/MachineBasicBlock.cpp b/lib/CodeGen/MachineBasicBlock.cpp
index 813fad288e..b5904443a8 100644
--- a/lib/CodeGen/MachineBasicBlock.cpp
+++ b/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;
 }
 
 void MachineBasicBlock::dump() const {
diff --git a/lib/CodeGen/PHIElimination.cpp b/lib/CodeGen/PHIElimination.cpp
index 923fa213e7..81ae3618ee 100644
--- a/lib/CodeGen/PHIElimination.cpp
+++ b/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!");