[HLSL] Create HLSL legalization passes

[s-perron]

The semantics of HLSL require passes some passes to be run that will
modify the llvm-ir created by clang to match what is expected by the
backend.

In this PR, wewe move the DXILFinalizeLinkage to be run for all backend.
The pass is also renamed to HLSLFinalizeLinkage. A pass of the global opt
pass is run afterwards.

Fixes #122767.

[s-perron]

Resources without explicit register assignments are not supported yet. If we do not do this then we end up with a handle that is zero initialized, which causes problems.

[github-actions]

⚠️ C/C++ code formatter, clang-format found issues in your code. ⚠️

You can test this locally with the following command:

git-clang-format --diff 6518b121f037717fd211c36659f7b25266424719 834f6be33005c6fd289e776ad5dbeeebc5509695 --extensions cpp,h -- clang/lib/CodeGen/BackendUtil.cpp llvm/lib/Target/DirectX/DirectXTargetMachine.cpp llvm/include/llvm/Transforms/HLSL/HLSLFinalizeLinkage.h llvm/lib/Transforms/HLSL/HLSLFinalizeLinkage.cpp

View the diff from clang-format here.

diff --git a/llvm/lib/Transforms/HLSL/HLSLFinalizeLinkage.cpp b/llvm/lib/Transforms/HLSL/HLSLFinalizeLinkage.cpp
index 8b0b6ea1c1..143349b6c5 100644
--- a/llvm/lib/Transforms/HLSL/HLSLFinalizeLinkage.cpp
+++ b/llvm/lib/Transforms/HLSL/HLSLFinalizeLinkage.cpp
@@ -18,7 +18,7 @@ using namespace llvm;
 static bool finalizeLinkage(Module &M) {
   SmallPtrSet<Function *, 8> Funcs;
 
-  for(auto &Var : M.globals()) {
+  for (auto &Var : M.globals()) {
     if (Var.getLinkage() == GlobalValue::ExternalLinkage) {
       Var.setLinkage(GlobalValue::InternalLinkage);
     }

[s-perron]

@llvm-beanz Let me know if this is a reasonable direction to go. I'll have update a lot of tests, and I don't want to do that unless we believe this is what we would like to do.

[bogner]

Sharing the code here makes sense to me, however, this does make the pass run significantly earlier in the DXIL pipeline. That might be fine but we'll have to make sure we aren't creating dead functions in any of the other DXIL backend passes that might have been cleaned up by this so far.