[Debuginfo][TailCallElim] Fix #86262: drop the debug location of entry branch (#86269)

This pr fixes #86262.

---------

Co-authored-by: Stephen Tozer <[email protected]>

Author: Apochens

llvm/lib/Transforms/Scalar/TailRecursionElimination.cpp

@@ -510,7 +510,9 @@ void TailRecursionEliminator::createTailRecurseLoopHeader(CallInst *CI) {
   NewEntry->takeName(HeaderBB);
   HeaderBB->setName("tailrecurse");
   BranchInst *BI = BranchInst::Create(HeaderBB, NewEntry);
-  BI->setDebugLoc(CI->getDebugLoc());
+  // If the new branch preserves the debug location of CI, it could result in
+  // misleading stepping, if CI is located in a conditional branch.
+  // So, here we don't give any debug location to BI.
 
   // Move all fixed sized allocas from HeaderBB to NewEntry.
   for (BasicBlock::iterator OEBI = HeaderBB->begin(), E = HeaderBB->end(),

llvm/test/Transforms/TailCallElim/debugloc.ll

@@ -4,13 +4,13 @@
 define void @foo() {
 entry:
 ; CHECK-LABEL: entry:
-; CHECK: br label %tailrecurse, !dbg ![[DbgLoc:[0-9]+]]
+; CHECK: br label %tailrecurse{{$}}
 
   call void @foo()                            ;; line 1
   ret void
 
 ; CHECK-LABEL: tailrecurse:
-; CHECK: br label %tailrecurse, !dbg ![[DbgLoc]]
+; CHECK: br label %tailrecurse, !dbg ![[DbgLoc:[0-9]+]]
 }
 
 ;; Make sure tailrecurse has the call instruction's DL