[llvm-dlltool] Use EXPORTAS name type for renamed imports on ARM64EC. (#99346)

Summary:
Renamed entries are more tricky on ARM64EC than on other targets due
to additional symbols (we need `__imp_aux_*` in addition to `__imp_*`
and both mangled and unmangled symbol thunks). While we could extend
weak aliases to add them, it seems cleaner to just always use EXPORTAS
name type on ARM64EC targets. Unlike other targets, linkers supporting
ARM64EC need to support EXPORTAS, so there is no compatibility problem
with that.

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Differential Revision: https://phabricator.intern.facebook.com/D60251341

Author: cjacek

llvm/lib/Object/COFFImportFile.cpp

@@ -729,7 +729,10 @@ Error writeImportLibrary(StringRef ImportName, StringRef Path,
         else if (Machine == IMAGE_FILE_MACHINE_I386 &&
                  applyNameType(IMPORT_NAME_NOPREFIX, Name) == E.ImportName)
           NameType = IMPORT_NAME_NOPREFIX;
-        else if (Name == E.ImportName)
+        else if (isArm64EC(M)) {
+          NameType = IMPORT_NAME_EXPORTAS;
+          ExportName = E.ImportName;
+        } else if (Name == E.ImportName)
           NameType = IMPORT_NAME;
         else {
           Deferred D;

llvm/test/tools/llvm-dlltool/arm64ec.test

@@ -44,6 +44,29 @@ RUN: llvm-nm --print-armap test3.lib | FileCheck --check-prefix=ARMAP2 %s
 RUN: not llvm-dlltool -m arm64 -d test.def -N test2.def -l test4.lib 2>&1 | FileCheck --check-prefix=ERR %s
 ERR: native .def file is supported only on arm64ec target
 
+RUN: llvm-dlltool -m arm64ec -d test3.def -l test3.lib
+RUN: llvm-readobj test3.lib | FileCheck --check-prefix=ALIAS %s
+
+ALIAS:      File: test.dll
+ALIAS-NEXT: Format: COFF-import-file-ARM64EC
+ALIAS-NEXT: Type: code
+ALIAS-NEXT: Name type: export as
+ALIAS-NEXT: Export name: efunc
+ALIAS-NEXT: Symbol: __imp_func
+ALIAS-NEXT: Symbol: func
+ALIAS-NEXT: Symbol: __imp_aux_func
+ALIAS-NEXT: Symbol: #func
+ALIAS-EMPTY:
+ALIAS-NEXT: File: test.dll
+ALIAS-NEXT: Format: COFF-import-file-ARM64EC
+ALIAS-NEXT: Type: code
+ALIAS-NEXT: Name type: export as
+ALIAS-NEXT: Export name: efunc
+ALIAS-NEXT: Symbol: __imp_efunc
+ALIAS-NEXT: Symbol: efunc
+ALIAS-NEXT: Symbol: __imp_aux_efunc
+ALIAS-NEXT: Symbol: #efunc
+
 #--- test.def
 LIBRARY test.dll
 EXPORTS
@@ -53,3 +76,9 @@ EXPORTS
 LIBRARY test.dll
 EXPORTS
     otherfunc
+
+#--- test3.def
+LIBRARY test.dll
+EXPORTS
+    func == efunc
+    efunc