[lld] [LLD] [COFF] Fix handling of comdat .drectve sections (PR #68116)

[Reid Kleckner via llvm-commits]

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@@ -660,10 +660,15 @@ std::optional<Symbol *> ObjFile::createDefined(
 
     if (prevailing) {
       SectionChunk *c = readSection(sectionNumber, def, getName());
-      sparseChunks[sectionNumber] = c;
-      c->sym = cast<DefinedRegular>(leader);
-      c->selection = selection;
-      cast<DefinedRegular>(leader)->data = &c->repl;
+      if (c) {
+        sparseChunks[sectionNumber] = c;
+        c->sym = cast<DefinedRegular>(leader);
+        c->selection = selection;
+        cast<DefinedRegular>(leader)->data = &c->repl;
+      } else {
+        sparseChunks[sectionNumber] = nullptr;
+        return nullptr;
+      }
     } else {
       sparseChunks[sectionNumber] = nullptr;
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rnk wrote:

I see three assignments to `sparseChunks[sectionNumber]`, can we reduce nesting and arrange the code so that we store a variable which is sometimes null?

For your code change, essentially wrap the `c->` expressions in the `if (c)` check.

Is the `return nullptr` necessary, or can we return `leader`?

https://github.com/llvm/llvm-project/pull/68116