[lld] [LLD][COFF] Add EC alias symbols for undefined x86_64 symbols on ARM64EC target (PR #114466)

[Martin Storsjö via llvm-commits]

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@@ -534,7 +534,22 @@ void ObjFile::initializeSymbols() {
 
 Symbol *ObjFile::createUndefined(COFFSymbolRef sym, bool overrideLazy) {
   StringRef name = check(coffObj->getSymbolName(sym));
-  return ctx.symtab.addUndefined(name, this, overrideLazy);
+  Symbol *s = ctx.symtab.addUndefined(name, this, overrideLazy);
+
+  // Add an anti-dependency alias for undefined AMD64 symbols on the ARM64EC
+  // target.
+  if (isArm64EC(ctx.config.machine) && getMachineType() == AMD64) {
+    auto u = dyn_cast<Undefined>(s);
+    if (u && !u->weakAlias) {
+      if (std::optional<std::string> mangledName =
+              getArm64ECMangledFunctionName(name)) {
+        Symbol *m =
+            ctx.symtab.addUndefined(saver().save(*mangledName), this, false);
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mstorsjo wrote:

Side note; literal bool parameters like false here, and true on the line below are quite hard to grasp unless you’re reading the called method at the same time. I think it may be more understandable if we’d add comments for these parameters about what they are; we have a pattern for that, `/*name=*/ false` (modulo spacing, I don’t remember what our canonical spacing is for these comments), which might make it clearer.

https://github.com/llvm/llvm-project/pull/114466