[SPIRV] Add shadow function when only global variable declared in the module

[YixingZhang007]

This PR is still working in progress. Thank you for your understanding!

[llvmbot]

@llvm/pr-subscribers-backend-spir-v

Author: None (YixingZhang007)

Changes

---

Full diff: https://github.com/llvm/llvm-project/pull/164829.diff

1 Files Affected:

• (modified) llvm/lib/Target/SPIRV/SPIRVEmitIntrinsics.cpp (+30)

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);

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diff --git a/llvm/lib/Target/SPIRV/SPIRVEmitIntrinsics.cpp b/llvm/lib/Target/SPIRV/SPIRVEmitIntrinsics.cpp
index f39670f5a..2182d4ad0 100644
--- a/llvm/lib/Target/SPIRV/SPIRVEmitIntrinsics.cpp
+++ b/llvm/lib/Target/SPIRV/SPIRVEmitIntrinsics.cpp
@@ -3025,25 +3025,25 @@ bool SPIRVEmitIntrinsics::runOnModule(Module &M) {
 
   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;
-          }
+    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();