[llvm] [DirectX] Implement the ForwardHandleAccesses pass (PR #135378)

[Helena Kotas via llvm-commits]

================
@@ -0,0 +1,165 @@
+//===- DXILForwardHandleAccesses.cpp - Cleanup Handles --------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "DXILForwardHandleAccesses.h"
+#include "DXILShaderFlags.h"
+#include "DirectX.h"
+#include "llvm/Analysis/DXILResource.h"
+#include "llvm/Analysis/Loads.h"
+#include "llvm/IR/DiagnosticInfo.h"
+#include "llvm/IR/Dominators.h"
+#include "llvm/IR/IntrinsicInst.h"
+#include "llvm/IR/Intrinsics.h"
+#include "llvm/IR/IntrinsicsDirectX.h"
+#include "llvm/IR/Module.h"
+#include "llvm/InitializePasses.h"
+#include "llvm/Pass.h"
+#include "llvm/Transforms/Utils/Local.h"
+
+#define DEBUG_TYPE "dxil-forward-handle-accesses"
+
+using namespace llvm;
+
+static void diagnoseAmbiguousHandle(IntrinsicInst *NewII,
+                                    IntrinsicInst *PrevII) {
+  Function *F = NewII->getFunction();
+  LLVMContext &Context = F->getParent()->getContext();
+  Context.diagnose(DiagnosticInfoGeneric(
+      Twine("Handle at \"") + NewII->getName() + "\" overwrites handle at \"" +
+      PrevII->getName() + "\""));
+}
+
+static void diagnoseHandleNotFound(LoadInst *LI) {
+  Function *F = LI->getFunction();
+  LLVMContext &Context = F->getParent()->getContext();
+  Context.diagnose(DiagnosticInfoGeneric(
+      LI, Twine("Load of \"") + LI->getPointerOperand()->getName() +
+              "\" is not a global resource handle"));
+}
+
+static void diagnoseUndominatedLoad(LoadInst *LI, IntrinsicInst *Handle) {
+  Function *F = LI->getFunction();
+  LLVMContext &Context = F->getParent()->getContext();
+  Context.diagnose(DiagnosticInfoGeneric(
+      LI, Twine("Load at \"") + LI->getName() +
+              "\" is not dominated by handle creation at \"" +
+              Handle->getName() + "\""));
+}
+
+static void
+processHandle(IntrinsicInst *II,
+              DenseMap<GlobalVariable *, IntrinsicInst *> &HandleMap) {
+  for (User *U : II->users())
+    if (auto *SI = dyn_cast<StoreInst>(U))
+      if (auto *GV = dyn_cast<GlobalVariable>(SI->getPointerOperand())) {
+        auto Entry = HandleMap.try_emplace(GV, II);
+        if (Entry.second)
+          LLVM_DEBUG(dbgs() << "Added " << GV->getName() << " to handle map\n");
+        else
+          diagnoseAmbiguousHandle(II, Entry.first->second);
+      }
+}
+
+static bool forwardHandleAccesses(Function &F, DominatorTree &DT) {
+  bool Changed = false;
+
+  DenseMap<GlobalVariable *, IntrinsicInst *> HandleMap;
+  SmallVector<LoadInst *> LoadsToProcess;
+  for (BasicBlock &BB : F)
+    for (Instruction &Inst : BB)
+      if (auto *II = dyn_cast<IntrinsicInst>(&Inst)) {
+        switch (II->getIntrinsicID()) {
+        case Intrinsic::dx_resource_handlefrombinding:
+          processHandle(II, HandleMap);
+          break;
+        default:
+          continue;
+        }
----------------
hekota wrote:

Just curious - why is this not an`if`? Are you expecting more cases to add later on?
```
if (II->getIntrinsicID() == Intrinsic::dx_resource_handlefrombinding)
 processHandle(II, HandleMap);
```

https://github.com/llvm/llvm-project/pull/135378