[clang] [LifetimeSafety] Add multi-block support to buildOriginFlowChain (PR #204592)

[Yuan Suo via cfe-commits]

================
@@ -235,20 +290,17 @@ class AnalysisImpl
       CurrOID = SrcOriginID;
     }
 
-    // FIXME: Ideally, this return is unreachable and should be an assert
-    // because we expect to always finish at an IssueFact. But since current
-    // traversal is limited to a single CFG block, multi-block OriginFlowChain
-    // construction might miss the IssueFact. We should add llvm_unreachable
-    // here once multi-block support is implemented.
-    return {};
+    return {OriginFlowChain, false};
----------------
suoyuan666 wrote:

Because the entry point has been changed to use the multi-block implementation of `buildOriginFlowChain` instead of this function, the case where the target `IssueFact` cannot be found and the function returns should be treated as a normal situation.

https://github.com/llvm/llvm-project/pull/204592