[lld][WebAssembly] Fix stub library deps causing LTO archive members to be required post-LTO (#101894)

Fixes: emscripten-core/emscripten#16836

Author: sbc100

lld/test/wasm/lto/stub-library.s

@@ -1,12 +1,21 @@
+## The function `bar` is declared in stub.so and depends on `foo` which is
+## defined in an LTO object.  We also test the case where the LTO object is
+## with an archive file.
+## This verifies that stub library dependencies (which are required exports) can
+## be defined in LTO objects, even when they are within archive files.
+
 # RUN: llvm-mc -filetype=obj -triple=wasm32-unknown-unknown -o %t.o %s
-# RUN: llvm-as %S/Inputs/foo.ll -o %t1.o
-# RUN: wasm-ld %t.o %t1.o %p/Inputs/stub.so -o %t.wasm
+# RUN: mkdir -p %t
+# RUN: llvm-as %S/Inputs/foo.ll -o %t/foo.o
+# RUN: wasm-ld %t.o %t/foo.o %p/Inputs/stub.so -o %t.wasm
 # RUN: obj2yaml %t.wasm | FileCheck %s
 
-# The function `bar` is declared in stub.so and depends on `foo`, which happens
-# be in an LTO object.
-# This verifies that stub library dependencies (required exports) can be defined
-# in LTO objects.
+## Run the same test but with foo.o inside of an archive file.
+# RUN: rm -f %t/libfoo.a
+# RUN: llvm-ar rcs %t/libfoo.a %t/foo.o
+# RUN: wasm-ld %t.o %t/libfoo.a %p/Inputs/stub.so -o %t2.wasm
+# RUN: obj2yaml %t2.wasm | FileCheck %s
+
 .functype bar () -> ()
 
 .globl _start

lld/wasm/Driver.cpp

@@ -949,6 +949,17 @@ static void processStubLibrariesPreLTO() {
           auto* needed = symtab->find(dep);
           if (needed ) {
             needed->isUsedInRegularObj = true;
+            // Like with handleLibcall we have to extract any LTO archive
+            // members that might need to be exported due to stub library
+            // symbols being referenced.  Without this the LTO object could be
+            // extracted during processStubLibraries, which is too late since
+            // LTO has already being performed at that point.
+            if (needed->isLazy() && isa<BitcodeFile>(needed->getFile())) {
+              if (!config->whyExtract.empty())
+                ctx.whyExtractRecords.emplace_back(toString(stub_file),
+                                                   needed->getFile(), *needed);
+              cast<LazySymbol>(needed)->extract();
+            }
           }
         }
       }

lld/wasm/InputFiles.cpp

@@ -744,7 +744,7 @@ Symbol *ObjFile::createUndefined(const WasmSymbol &sym, bool isCalledDirectly) {
   llvm_unreachable("unknown symbol kind");
 }
 
-StringRef strip(StringRef s) { return s.trim(' '); }
+static StringRef strip(StringRef s) { return s.trim(' '); }
 
 void StubFile::parse() {
   bool first = true;
@@ -761,7 +761,7 @@ void StubFile::parse() {
     }
 
     // Lines starting with # are considered comments
-    if (line.starts_with("#"))
+    if (line.starts_with("#") || !line.size())
       continue;
 
     StringRef sym;