[TRE][DebugInfo] Preserve Debug Location in new branch instruction

[gramanas]

Summary

https://bugs.llvm.org/show_bug.cgi?id=38179

The DL is the one from the call instruction.

There are two branch instructions created
so the new test covers them both.

[gramanas]

• typo

[vsk]

Looks great, thanks!

lib/Transforms/Scalar/TailRecursionElimination.cpp

static bool eliminateRecursiveTailCall(CallInst *CI, ReturnInst *Ret,
 
   // OK! We can transform this tail call.  If this is the first one found,
   // create the new entry block, allowing us to branch back to the old entry.
   if (!OldEntry) {
     OldEntry = &F->getEntryBlock();
     BasicBlock *NewEntry = BasicBlock::Create(F->getContext(), "", F, OldEntry);
     NewEntry->takeName(OldEntry);
     OldEntry->setName("tailrecurse");
-    BranchInst::Create(OldEntry, NewEntry);
+    BranchInst *BI = BranchInst::Create(OldEntry, NewEntry);
+    BI->setDebugLoc(CI->getDebugLoc());
 
     // If this tail call is marked 'tail' and if there are any allocas in the
     // entry block, move them up to the new entry block.
     TailCallsAreMarkedTail = CI->isTailCall();
     if (TailCallsAreMarkedTail)
       // Move all fixed sized allocas from OldEntry to NewEntry.
       for (BasicBlock::iterator OEBI = OldEntry->begin(), E = OldEntry->end(),
              NEBI = NewEntry->begin(); OEBI != E; )

test/Transforms/TailCallElim/debugloc.ll

+; RUN: opt < %s -debugify -tailcallelim -S | FileCheck %s
+
+define void @foo() {
+entry:
+; CHECK-LABEL: entry:
+; CHECK: br label %tailrecurse, !dbg ![[DbgLoc:[0-9]+]]
+
+  call void @foo()                            ;; line 1
+  ret void
+
+; CHECK-LABEL: tailrecurse:
+; CHECK: br label %tailrecurse, !dbg ![[DbgLoc]]
+}
+
+;; Make sure tailrecurse has the call instruction's DL
+; CHECK: ![[DbgLoc]] = !DILocation(line: 1