[ELF] Move demoteSymbols to Writer.cpp. NFC

History of demoteSharedSymbols:

* https://reviews.llvm.org/D45536 demotes SharedSymbol
* https://reviews.llvm.org/D111365 demotes lazy symbols
* The pending #69295 will demote symbols defined in discarded sections

The pass is placed after markLive just to be clear that it needs `isNeeded`
information computed by markLive. The remaining passes in Driver.cpp do not use
symbol information. Move the pass to Writer.cpp to be closer to other
symbol-related passes.

Author: MaskRay

lld/ELF/Driver.cpp

@@ -2248,24 +2248,6 @@ static void replaceCommonSymbols() {
   }
 }
 
-// If all references to a DSO happen to be weak, the DSO is not added to
-// DT_NEEDED. If that happens, replace ShardSymbol with Undefined to avoid
-// dangling references to an unneeded DSO. Use a weak binding to avoid
-// --no-allow-shlib-undefined diagnostics. Similarly, demote lazy symbols.
-static void demoteSharedAndLazySymbols() {
-  llvm::TimeTraceScope timeScope("Demote shared and lazy symbols");
-  for (Symbol *sym : symtab.getSymbols()) {
-    auto *s = dyn_cast<SharedSymbol>(sym);
-    if (!(s && !cast<SharedFile>(s->file)->isNeeded) && !sym->isLazy())
-      continue;
-
-    uint8_t binding = sym->isLazy() ? sym->binding : uint8_t(STB_WEAK);
-    Undefined(nullptr, sym->getName(), binding, sym->stOther, sym->type)
-        .overwrite(*sym);
-    sym->versionId = VER_NDX_GLOBAL;
-  }
-}
-
 // The section referred to by `s` is considered address-significant. Set the
 // keepUnique flag on the section if appropriate.
 static void markAddrsig(Symbol *s) {
@@ -3023,7 +3005,6 @@ void LinkerDriver::link(opt::InputArgList &args) {
 
   // Garbage collection and removal of shared symbols from unused shared objects.
   invokeELFT(markLive,);
-  demoteSharedAndLazySymbols();
 
   // Make copies of any input sections that need to be copied into each
   // partition.

lld/ELF/Writer.cpp

@@ -251,6 +251,23 @@ void elf::addReservedSymbols() {
   ElfSym::edata2 = add("_edata", -1);
 }
 
+// If all references to a DSO happen to be weak, the DSO is not added to
+// DT_NEEDED. If that happens, replace ShardSymbol with Undefined to avoid
+// dangling references to an unneeded DSO. Use a weak binding to avoid
+// --no-allow-shlib-undefined diagnostics. Similarly, demote lazy symbols.
+static void demoteSymbols() {
+  llvm::TimeTraceScope timeScope("Demote symbols");
+  for (Symbol *sym : symtab.getSymbols()) {
+    auto *s = dyn_cast<SharedSymbol>(sym);
+    if (!(s && !cast<SharedFile>(s->file)->isNeeded) && !sym->isLazy())
+      continue;
+    uint8_t binding = sym->isLazy() ? sym->binding : uint8_t(STB_WEAK);
+    Undefined(nullptr, sym->getName(), binding, sym->stOther, sym->type)
+        .overwrite(*sym);
+    sym->versionId = VER_NDX_GLOBAL;
+  }
+}
+
 // Fully static executables don't support MTE globals at this point in time, as
 // we currently rely on:
 //   - A dynamic loader to process relocations, and
@@ -1935,12 +1952,13 @@ template <class ELFT> void Writer<ELFT>::finalizeSections() {
       for (Partition &part : partitions)
         finalizeSynthetic(part.ehFrame.get());
     }
+  }
 
-    if (config->hasDynSymTab) {
-      parallelForEach(symtab.getSymbols(), [](Symbol *sym) {
-        sym->isPreemptible = computeIsPreemptible(*sym);
-      });
-    }
+  demoteSymbols();
+  if (config->hasDynSymTab) {
+    parallelForEach(symtab.getSymbols(), [](Symbol *sym) {
+      sym->isPreemptible = computeIsPreemptible(*sym);
+    });
   }
 
   // Change values of linker-script-defined symbols from placeholders (assigned