[llvm] [DirectX] Convert private global variables to internal linkage during Finalize Linkage pass (PR #146406)

[Kaitlin Peng via llvm-commits]

https://github.com/kmpeng created https://github.com/llvm/llvm-project/pull/146406

Fixes #140420. The switch.table.* validation errors were caused by DXIL not supporting private global variables. Converting them to internal linkage fixes the bug.

May need more discussion on the preserved analyses/a follow-up PR that fixes what this pass says it preserves.

>From 6a3aedc006a26e29908c731f3a4407b3b629169d Mon Sep 17 00:00:00 2001
From: kmpeng <kaitlinpeng at microsoft.com>
Date: Mon, 30 Jun 2025 11:30:50 -0700
Subject: [PATCH] fix switch.table.* bug - convert private global variables to
 internal linkage

---
 .../Target/DirectX/DXILFinalizeLinkage.cpp    | 20 ++++++++++++++++---
 1 file changed, 17 insertions(+), 3 deletions(-)

diff --git a/llvm/lib/Target/DirectX/DXILFinalizeLinkage.cpp b/llvm/lib/Target/DirectX/DXILFinalizeLinkage.cpp
index 94b2dbe78c4f7..5f331dbd2d826 100644
--- a/llvm/lib/Target/DirectX/DXILFinalizeLinkage.cpp
+++ b/llvm/lib/Target/DirectX/DXILFinalizeLinkage.cpp
@@ -18,6 +18,16 @@
 using namespace llvm;
 
 static bool finalizeLinkage(Module &M) {
+  bool MadeChange = false;
+
+  // Convert private global variables to internal linkage.
+  for (GlobalVariable &GV : M.globals()) {
+    if (GV.hasPrivateLinkage()) {
+      GV.setLinkage(GlobalValue::InternalLinkage);
+      MadeChange = true;
+    }
+  }
+
   SmallVector<Function *> Funcs;
 
   // Collect non-entry and non-exported functions to set to internal linkage.
@@ -32,13 +42,17 @@ static bool finalizeLinkage(Module &M) {
   }
 
   for (Function *F : Funcs) {
-    if (F->getLinkage() == GlobalValue::ExternalLinkage)
+    if (F->getLinkage() == GlobalValue::ExternalLinkage) {
       F->setLinkage(GlobalValue::InternalLinkage);
-    if (F->isDefTriviallyDead())
+      MadeChange = true;
+    }
+    if (F->isDefTriviallyDead()) {
       M.getFunctionList().erase(F);
+      MadeChange = true;
+    }
   }
 
-  return false;
+  return MadeChange;
 }
 
 PreservedAnalyses DXILFinalizeLinkage::run(Module &M,