Fix wrong assertion failure.

Previously, if you have foo=bar in a definition file, this assertion
could fire because when symbols are read from file they could be mangled.
It seems that due to historical reasons underscore mangling scheme is
really ad-hoc, and I cannot find a clean way to handle this. I had
to just de-mangle symbols to search again.

llvm-svn: 297357

lld/COFF/Librarian.cpp

@@ -104,6 +104,14 @@ static ImportNameType getNameType(StringRef Sym, StringRef ExtName) {
 
 static std::string replace(StringRef S, StringRef From, StringRef To) {
   size_t Pos = S.find(From);
+
+  // From and To may be mangled, but substrings in S may not.
+  if (Pos == StringRef::npos && From.startswith("_") && To.startswith("_")) {
+    From = From.substr(1);
+    To = To.substr(1);
+    Pos = S.find(From);
+  }
+
   if (Pos == StringRef::npos) {
     error(S + ": replacing '" + From + "' with '" + To + "' failed");
     return "";

lld/test/COFF/export32.test

@@ -73,6 +73,16 @@
 # CHECK6:     duplicate /export option: _exportfn2
 # CHECK6-NOT: duplicate /export option: _exportfn1
 
+# RUN: lld-link /out:%t.dll /dll %t.obj /export:foo=mangled
+# RUN: llvm-objdump -p %t.dll | FileCheck -check-prefix=CHECK7 %s
+
+# CHECK7:      Export Table:
+# CHECK7:      DLL name: export32.test.tmp.dll
+# CHECK7:      Ordinal      RVA  Name
+# CHECK7-NEXT:       0        0
+# CHECK7-NEXT:       1        0
+# CHECK7-NEXT:       2   0x1010  foo
+
 --- !COFF
 header:
   Machine:         IMAGE_FILE_MACHINE_I386