[NFC][Utils] deleteDeadLoop(): add an assert that exit block has some non-PHI instruction

Summary:
If `deleteDeadLoop()` is called on such a loop, that has "bad" exit block,
one that e.g. has no terminator instruction, the `DIBuilder::insertDbgValueIntrinsic()`
will be told to insert the Dbg Value Intrinsic after `nullptr`
(since there is no first non-PHI instruction), which will cause it to not insert
those instructions into any basic block. The instructions will be parent-less,
and IR verifier will complain. It is rather obvious to track down the root cause
when that happens, so let's just assert it never happens.

Reviewers: sanjoy, davide, vsk

Reviewed By: vsk

Subscribers: llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D61008

llvm-svn: 359993

1 files changed, 7 insertions, 3 deletions

diff --git a/llvm/lib/Transforms/Utils/LoopUtils.cpp b/llvm/lib/Transforms/Utils/LoopUtils.cpp
index 045cb6284c4..16971b2edbb 100644
--- a/llvm/lib/Transforms/Utils/LoopUtils.cpp
+++ b/llvm/lib/Transforms/Utils/LoopUtils.cpp
@@ -584,10 +584,14 @@ void llvm::deleteDeadLoop(Loop *L, DominatorTree *DT = nullptr,
   // dbg.value truncates the range of any dbg.value before the loop where the
   // loop used to be. This is particularly important for constant values.
   DIBuilder DIB(*ExitBlock->getModule());
+  Instruction *InsertDbgValueBefore = ExitBlock->getFirstNonPHI();
+  assert(InsertDbgValueBefore &&
+         "There should be a non-PHI instruction in exit block, else these "
+         "instructions will have no parent.");
   for (auto *DVI : DeadDebugInst)
-    DIB.insertDbgValueIntrinsic(
-        UndefValue::get(Builder.getInt32Ty()), DVI->getVariable(),
-        DVI->getExpression(), DVI->getDebugLoc(), ExitBlock->getFirstNonPHI());
+    DIB.insertDbgValueIntrinsic(UndefValue::get(Builder.getInt32Ty()),
+                                DVI->getVariable(), DVI->getExpression(),
+                                DVI->getDebugLoc(), InsertDbgValueBefore);
 
   // Remove the block from the reference counting scheme, so that we can
   // delete it freely later.