[NFC][DebugInfo] Rewrite more call-sites to insert with iterators (#124288)

As part of the "RemoveDIs" work to eliminate debug intrinsics, we're
replacing methods that use Instruction*'s as positions with iterators. The
call-sites updated in this patch are those where the dyn_cast_or_null cast
utility doesn't compose well with iterator insertion. It can distinguish
between nullptr and a "present" (non-null) Instruction pointer, but not
between a legal and illegal instruction iterator. This can lead to
end-iterator dereferences and thus crashes.

We can improve this in the future (as parent-pointers can now be accessed
from ilist nodes), but for the moment, add explicit tests for end()
iterators at the five call sites affected by this.

1 files changed, 4 insertions, 2 deletions

diff --git a/llvm/lib/IR/Verifier.cpp b/llvm/lib/IR/Verifier.cpp
index 54de812..8432779 100644
--- a/llvm/lib/IR/Verifier.cpp
+++ b/llvm/lib/IR/Verifier.cpp
@@ -6521,8 +6521,10 @@ void Verifier::visitIntrinsicCall(Intrinsic::ID ID, CallBase &Call) {
       const ColorVector &CV = BlockEHFuncletColors.find(CallBB)->second;
       assert(CV.size() > 0 && "Uncolored block");
       for (BasicBlock *ColorFirstBB : CV)
-        if (dyn_cast_or_null<FuncletPadInst>(ColorFirstBB->getFirstNonPHI()))
-          InEHFunclet = true;
+        if (auto It = ColorFirstBB->getFirstNonPHIIt();
+            It != ColorFirstBB->end())
+          if (dyn_cast_or_null<FuncletPadInst>(&*It))
+            InEHFunclet = true;
 
       // Check for funclet operand bundle
       bool HasToken = false;