[IR] Use EXPORTAS for ARM64EC mangled symbols with dllexport attribut…

…e. (#81940)

We currently just use mangled name. This works fine, because linker
should detect that and demangle it for the export table. However, on
MSVC, the compiler is more specific and passes demangled name as well,
with EXPORTAS. This PR aims to match that. MSVC doesn't use quotes in
this case, so I added '#' to the list of characters that don't need it.

llvm/lib/IR/Mangler.cpp

@@ -18,8 +18,10 @@
 #include "llvm/IR/DerivedTypes.h"
 #include "llvm/IR/Function.h"
 #include "llvm/IR/Module.h"
+#include "llvm/Object/COFF.h"
 #include "llvm/Support/raw_ostream.h"
 #include "llvm/TargetParser/Triple.h"
+
 using namespace llvm;
 
 namespace {
@@ -192,7 +194,7 @@ void Mangler::getNameWithPrefix(SmallVectorImpl<char> &OutName,
 
 // Check if the name needs quotes to be safe for the linker to interpret.
 static bool canBeUnquotedInDirective(char C) {
-  return isAlnum(C) || C == '_' || C == '@';
+  return isAlnum(C) || C == '_' || C == '@' || C == '#';
 }
 
 static bool canBeUnquotedInDirective(StringRef Name) {
@@ -233,6 +235,16 @@ void llvm::emitLinkerFlagsForGlobalCOFF(raw_ostream &OS, const GlobalValue *GV,
     } else {
       Mangler.getNameWithPrefix(OS, GV, false);
     }
+    if (TT.isWindowsArm64EC()) {
+      // Use EXPORTAS for mangled ARM64EC symbols.
+      // FIXME: During LTO, we're invoked prior to the EC lowering pass,
+      // so symbols are not yet mangled. Emitting the unmangled name
+      // typically functions correctly; the linker can resolve the export
+      // with the demangled alias.
+      if (std::optional<std::string> demangledName =
+              object::getArm64ECDemangledFunctionName(GV->getName()))
+        OS << ",EXPORTAS," << *demangledName;
+    }
     if (NeedQuotes)
       OS << "\"";
 

llvm/test/CodeGen/AArch64/dllexport.ll

@@ -1,5 +1,7 @@
 ; RUN: llc -mtriple aarch64-windows-gnu -filetype asm -o - %s | FileCheck %s -check-prefix CHECK -check-prefix CHECK-GNU
 ; RUN: llc -mtriple aarch64-windows-msvc -filetype asm -o - %s | FileCheck %s -check-prefix CHECK -check-prefix CHECK-MSVC
+; RUN: llc -mtriple arm64ec-windows-gnu -filetype asm -o - %s | FileCheck %s -check-prefix CHECK -check-prefix CHECK-GNU-EC
+; RUN: llc -mtriple arm64ec-windows-msvc -filetype asm -o - %s | FileCheck %s -check-prefix CHECK -check-prefix CHECK-MSVC-EC
 
 define void @f() {
   ret void
@@ -71,3 +73,40 @@ define weak_odr dllexport void @l() {
 ; CHECK-MSVC: .ascii "  /EXPORT:s"
 ; CHECK-MSVC: .ascii "  /EXPORT:t"
 ; CHECK-MSVC: .ascii "  /EXPORT:u"
+
+; CHECK-GNU-EC-NOT: -export:f
+; CHECK-GNU-EC-NOT: -export:#f,EXPORTAS,f
+; CHECK-GNU-EC: .ascii " -export:#g,EXPORTAS,g
+; CHECK-GNU-EC: .ascii " -export:#h,EXPORTAS,h
+; CHECK-GNU-EC-NOT: -export:i
+; CHECK-GNU-EC-NOT: -export:#i,EXPORTAS,i
+; CHECK-GNU-EC: .ascii " -export:#j,EXPORTAS,j"
+; CHECK-GNU-EC: .ascii " -export:#k,EXPORTAS,k"
+; CHECK-GNU-EC: .ascii " -export:#l,EXPORTAS,l"
+; CHECK-GNU-EC: .ascii " -export:m,data"
+; CHECK-GNU-EC: .ascii " -export:n,data"
+; CHECK-GNU-EC: .ascii " -export:o,data"
+; CHECK-GNU-EC: .ascii " -export:p,data"
+; CHECK-GNU-EC: .ascii " -export:q,data"
+; CHECK-GNU-EC: .ascii " -export:r"
+; CHECK-GNU-EC: .ascii " -export:s"
+; CHECK-GNU-EC: .ascii " -export:t"
+; CHECK-GNU-EC: .ascii " -export:u"
+; CHECK-MSVC-EC-NOT: /EXPORT:f
+; CHECK-MSVC-EC-NOT: /EXPORT:#f,EXPORTAS,f
+; CHECK-MSVC-EC: .ascii "  /EXPORT:#g,EXPORTAS,g"
+; CHECK-MSVC-EC: .ascii "  /EXPORT:#h,EXPORTAS,h"
+; CHECK-MSVC-EC-NOT: /EXPORT:i
+; CHECK-MSVC-EC-NOT: /EXPORT:#i,EXPORTAS,i
+; CHECK-MSVC-EC: .ascii "  /EXPORT:#j,EXPORTAS,j"
+; CHECK-MSVC-EC: .ascii "  /EXPORT:#k,EXPORTAS,k"
+; CHECK-MSVC-EC: .ascii "  /EXPORT:#l,EXPORTAS,l"
+; CHECK-MSVC-EC: .ascii "  /EXPORT:m,DATA"
+; CHECK-MSVC-EC: .ascii "  /EXPORT:n,DATA"
+; CHECK-MSVC-EC: .ascii "  /EXPORT:o,DATA"
+; CHECK-MSVC-EC: .ascii "  /EXPORT:p,DATA"
+; CHECK-MSVC-EC: .ascii "  /EXPORT:q,DATA"
+; CHECK-MSVC-EC: .ascii "  /EXPORT:r"
+; CHECK-MSVC-EC: .ascii "  /EXPORT:s"
+; CHECK-MSVC-EC: .ascii "  /EXPORT:t"
+; CHECK-MSVC-EC: .ascii "  /EXPORT:u"