[llvm] [SPIRV] Emit NonSemantic DebugGlobalVariable (PR #207230)

[Manuel Carrasco via llvm-commits]

================
@@ -251,6 +255,27 @@ void SPIRVNonSemanticDebugHandler::beginModule(Module *M) {
     if (!SP->isDefinition())
       SubprogramDeclarations.push_back(SP);
   }
+
+  // Map DIGlobalVariable -> llvm::GlobalVariable for globals that attach !dbg.
+  // The link lives on the IR global (via DIGlobalVariableExpression); DIGV
+  // metadata has no back-reference to its @g.
+  for (const GlobalVariable &G : M->globals()) {
+    SmallVector<DIGlobalVariableExpression *, 4> GVEs;
+    G.getDebugInfo(GVEs);
+    for (DIGlobalVariableExpression *GVE : GVEs)
+      DIGVToLLVMGV.try_emplace(GVE->getVariable(), &G);
+  }
+
+  // DebugInfoFinder deduplicates expressions but not by their pointed
+  // variables. We use a SmallSetVector to deduplicate them.
----------------
mgcarrasco wrote:

It seems to be the only one in clang, although it may also happen in the Fortran's front-end. Then, there are optimizations such as GlobalMerge. This is what the AI has found out.

https://github.com/llvm/llvm-project/blob/a163cf9268e89097dae55580f2ce2a1a7a99194b/llvm/test/Transforms/GlobalMerge/debug-info.ll#L7
https://github.com/llvm/llvm-project/blob/main/llvm/lib/CodeGen/GlobalMerge.cpp

https://github.com/llvm/llvm-project/pull/207230