[PATCH] D61008: [NFC][Utils] deleteDeadLoop(): add an assert that exit block has some non-PHI instruction

[Roman Lebedev via Phabricator via llvm-commits]

lebedev.ri created this revision.
lebedev.ri added reviewers: sanjoy, davide, vsk.
lebedev.ri added a project: LLVM.

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.


Repository:
  rL LLVM

https://reviews.llvm.org/D61008

Files:
  lib/Transforms/Utils/LoopUtils.cpp


Index: lib/Transforms/Utils/LoopUtils.cpp
===================================================================
--- lib/Transforms/Utils/LoopUtils.cpp
+++ lib/Transforms/Utils/LoopUtils.cpp
@@ -584,10 +584,14 @@
   // 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.


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