[llvm] [SPIRV] Add shadow function when only global variable declared in the module (PR #164829)

[via llvm-commits]

https://github.com/YixingZhang007 created https://github.com/llvm/llvm-project/pull/164829

…there is global variable but no function

>From 63ae5de4cf503c89d092d11d50ea15c548775955 Mon Sep 17 00:00:00 2001
From: y <yixing.zhang at intel.com>
Date: Wed, 22 Oct 2025 23:00:29 -0700
Subject: [PATCH] add initial solution by adding a shadow functin into the
 module when there is global variable but no function

---
 llvm/lib/Target/SPIRV/SPIRVEmitIntrinsics.cpp | 30 +++++++++++++++++++
 1 file changed, 30 insertions(+)

diff --git a/llvm/lib/Target/SPIRV/SPIRVEmitIntrinsics.cpp b/llvm/lib/Target/SPIRV/SPIRVEmitIntrinsics.cpp
index 9f2e07508a36a..64e076338816f 100644
--- a/llvm/lib/Target/SPIRV/SPIRVEmitIntrinsics.cpp
+++ b/llvm/lib/Target/SPIRV/SPIRVEmitIntrinsics.cpp
@@ -3013,6 +3013,36 @@ bool SPIRVEmitIntrinsics::runOnModule(Module &M) {
   parseFunDeclarations(M);
   insertConstantsForFPFastMathDefault(M);
 
+  // If there are no functions but there is at least one global variable,
+  // create a shadow function to "anchor" global handling in codegen.
+  bool HasAnyFunction = false;
+  for (auto &F : M)
+    if (!F.isDeclaration() && !F.isIntrinsic())
+      HasAnyFunction = true;
+
+  Function *ShadowFunc = nullptr;
+  if (!HasAnyFunction) {
+      for (auto GI = M.global_begin(), GE = M.global_end(); GI != GE; ) {
+          GlobalVariable *GV = &*GI++;
+          if (GV->hasInternalLinkage()) {
+              GV->eraseFromParent();
+              Changed = true;
+          } else if (ShadowFunc == nullptr) {
+              LLVMContext &Ctx = M.getContext();
+              auto *FTy = FunctionType::get(Type::getVoidTy(Ctx), /*isVarArg=*/false);
+              ShadowFunc = Function::Create(
+                  FTy, GlobalValue::InternalLinkage, "__spirv_globals_entry", &M);
+
+              // Create a basic block and insert a ret void
+              BasicBlock *BB = BasicBlock::Create(Ctx, "entry", ShadowFunc);
+              IRBuilder<> B(BB);
+              B.CreateRetVoid();
+
+              Changed = true;
+          }
+      }
+  }
+
   TodoType.clear();
   for (auto &F : M)
     Changed |= runOnFunction(F);