[lld] [LLD][COFF] Generate X64 thunks for ARM64EC entry points and patchable functions. (PR #105499)

[Martin Storsjö via llvm-commits]

================
@@ -1317,6 +1317,72 @@ void LinkerDriver::convertResources() {
   f->includeResourceChunks();
 }
 
+void LinkerDriver::maybeCreateECExportThunk(StringRef name, Symbol *&sym) {
+  Defined *def;
+  if (!sym)
+    return;
+  if (auto undef = dyn_cast<Undefined>(sym))
+    def = undef->getWeakAlias();
+  else
+    def = dyn_cast<Defined>(sym);
+  if (!def)
+    return;
+
+  if (def->getChunk()->getArm64ECRangeType() != chpe_range_type::Arm64EC)
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mstorsjo wrote:

Hmm, `getArm64ECRangeType()` return a `std::optional<>` - don't we usually need to somewhat check that it really is set and not nullopt, and then kinda unwrap/dereference it to get the actual value? Or I guess this does that, somewhat, and nullopt obviously returns true for the `operator!=`?

I.e., I presume this combo actually works on both GCC, Clang and MSVC, but have you tested that it works (and doesn't e.g. assert) on nullopt?

https://github.com/llvm/llvm-project/pull/105499