[TIR][Driver] Move ShouldAnnotateEntryFunc logic into transform (apac…

…he#14562)

* [TIR][Driver] Move ShouldAnnotateEntryFunc logic into transform

Prior to this commit, the `MixedModulePassManager` determined whether
the module should have its entry function annotated, while the
`AnnotateEntryFunc` validates that this condition was upheld,
duplicating the logic applied.  This commit moves the logic to
`AnnotateEntryFunc`, which is unconditionally called from the
`MixedModulePassManager`, but which is a no-op for cases where no
annotation is required.

* Maintain previous behavior for modules with one function

src/driver/driver_api.cc

@@ -71,13 +71,6 @@ bool LLVMEnabled() {
   return pf != nullptr;
 }
 
-bool ShouldAnnotateEntryFunc(const IRModule mod) {
-  Optional<tvm::relay::Executor> executor = mod->GetAttr<tvm::relay::Executor>("executor");
-  const bool aot_executor = executor.defined() && executor.value()->name == "aot";
-  const bool single_entry_func = (mod->functions.size() == 1);
-  return single_entry_func && !aot_executor;
-}
-
 /*! \return The default host target for a given device target */
 Target DefaultTargetHost(Target target) {
   if (target.defined() && target->GetTargetDeviceType() == kDLCPU) {
@@ -558,9 +551,7 @@ transform::Sequential MixedModulePassManager(IRModule mixed_mod, Target target)
 
   mixed_pass_list.push_back(tir::transform::VerifyMemory());
 
-  if (ShouldAnnotateEntryFunc(mixed_mod)) {
-    mixed_pass_list.push_back(tir::transform::AnnotateEntryFunc());
-  }
+  mixed_pass_list.push_back(tir::transform::AnnotateEntryFunc());
 
   bool detect_global_barrier =
       pass_ctx->GetConfig<Bool>("tir.detect_global_barrier", Bool(false)).value();

src/tir/transforms/primfunc_utils.cc

@@ -23,6 +23,7 @@
  */
 
 #include <tvm/driver/driver_api.h>
+#include <tvm/relay/executor.h>
 #include <tvm/tir/transform.h>
 
 namespace tvm {
@@ -40,11 +41,49 @@ transform::Pass BindTarget(Target target) {
 }
 
 transform::Pass AnnotateEntryFunc() {
-  auto fpass = [](tir::PrimFunc f, IRModule m, transform::PassContext ctx) {
-    ICHECK(m->functions.size() == 1);
-    return WithAttr(std::move(f), tir::attr::kIsEntryFunc, Bool(true));
+  auto fpass = [](IRModule mod, transform::PassContext ctx) -> IRModule {
+    // AOT tracks the entry function, no annotation required
+    auto executor = mod->GetAttr<tvm::relay::Executor>("executor");
+    const bool is_aot_executor = executor.defined() && executor.value()->name == "aot";
+    if (is_aot_executor) {
+      return mod;
+    }
+
+    // If only a single function exists, that function must be the entry
+    if (mod->functions.size() == 1) {
+      auto [gvar, base_func] = *mod->functions.begin();
+      if (!base_func->HasNonzeroAttr(tir::attr::kIsEntryFunc)) {
+        if (auto ptr = base_func.as<PrimFuncNode>()) {
+          mod->Update(gvar, WithAttr(GetRef<PrimFunc>(ptr), tir::attr::kIsEntryFunc, Bool(true)));
+        }
+      }
+      return mod;
+    }
+
+    // If the module has multiple functions, but only one is exposed
+    // externally, that function must be the entry.
+    bool has_external_non_primfuncs = false;
+    IRModule with_annotations;
+    for (const auto& [gvar, base_func] : mod->functions) {
+      bool is_external = base_func->GetAttr<String>(tvm::attr::kGlobalSymbol).defined();
+      if (is_external) {
+        if (auto ptr = base_func.as<PrimFuncNode>()) {
+          with_annotations->Add(
+              gvar, WithAttr(GetRef<PrimFunc>(ptr), tir::attr::kIsEntryFunc, Bool(true)));
+        } else {
+          has_external_non_primfuncs = true;
+        }
+      }
+    }
+    if (with_annotations->functions.size() == 1 && !has_external_non_primfuncs) {
+      mod->Update(with_annotations);
+      return mod;
+    }
+
+    // Default fallback, no annotations may be inferred.
+    return mod;
   };
-  return tir::transform::CreatePrimFuncPass(fpass, 0, "tir.AnnotateEntryFunc", {});
+  return tvm::transform::CreateModulePass(fpass, 0, "tir.AnnotateEntryFunc", {});
 }
 
 transform::Pass Filter(runtime::TypedPackedFunc<bool(PrimFunc)> fcond) {