[llvm] [BOLT][DWARF] Avoid unnecessary work if DWO id is zero (PR #154749)

[Jinjie Huang via llvm-commits]

https://github.com/Jinjie-Huang created https://github.com/llvm/llvm-project/pull/154749

DWOs with a DWOId of 0 are considered invalid. Currently, createRangeLocListAddressWriters() is called before these invalid DWOs are skipped, which seems unnecessary. Perhaps we can check the DWOId beforehand?

BTW, this may lead to an assertion failure inside createRangeLocListAddressWriters("RangeLists writer for DWO unit already exists.), when a duplicate DWO ID of 0 is encountered. I hit this case when using the compiler built prior to this [commit](https://github.com/llvm/llvm-project/commit/e731a2678c7cf81b1d3817489a52b519cb14f85e) with -fsplit-dwarf-inlining enabled, which generates a large number of Compile Units with a DWO ID == 0. I'm not sure if other scenarios could also trigger this issue.

>From 73d7ed229285659ba61123db52210e70d976516a Mon Sep 17 00:00:00 2001
From: huangjinjie <huangjinjie at bytedance.com>
Date: Thu, 21 Aug 2025 20:09:57 +0800
Subject: [PATCH] Avoid unnecessary work if DWO id is zero

---
 bolt/lib/Rewrite/DWARFRewriter.cpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/bolt/lib/Rewrite/DWARFRewriter.cpp b/bolt/lib/Rewrite/DWARFRewriter.cpp
index 0c1a1bac6c72e..e8f6189eb5a69 100644
--- a/bolt/lib/Rewrite/DWARFRewriter.cpp
+++ b/bolt/lib/Rewrite/DWARFRewriter.cpp
@@ -729,13 +729,13 @@ void DWARFRewriter::updateDebugInfo() {
     ThreadPoolInterface &ThreadPool =
         ParallelUtilities::getThreadPool(ThreadCount);
     for (DWARFUnit *CU : DIEBlder.getProcessedCUs()) {
-      createRangeLocListAddressWriters(*CU);
       std::optional<DWARFUnit *> SplitCU;
       std::optional<uint64_t> DWOId = CU->getDWOId();
       if (DWOId)
         SplitCU = BC.getDWOCU(*DWOId);
       if (!SplitCU)
         continue;
+      createRangeLocListAddressWriters(*CU);
       DebugAddrWriter &AddressWriter =
           *AddressWritersByCU[CU->getOffset()].get();
       DebugRangesSectionWriter &TempRangesSectionWriter =