[llvm] [AMDGPU] Introduce conditional barrier pseudo instruction (PR #171604)

[Matt Arsenault via llvm-commits]

================
@@ -0,0 +1,147 @@
+//===-- AMDGPUExpandCondBarrier.cpp - Expand conditional barriers ------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+//
+// This pass expands SI_COND_BARRIER pseudo instructions into conditional
+// control flow with actual barrier instructions.
+//
+//===----------------------------------------------------------------------===//
+
+#include "AMDGPU.h"
+#include "GCNSubtarget.h"
+#include "SIInstrInfo.h"
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/CodeGen/MachineBasicBlock.h"
+#include "llvm/CodeGen/MachineFunctionPass.h"
+#include "llvm/CodeGen/MachineInstrBuilder.h"
+#include "llvm/InitializePasses.h"
+
+using namespace llvm;
+
+#define DEBUG_TYPE "amdgpu-expand-cond-barrier"
+
+class AMDGPUExpandCondBarrier : public MachineFunctionPass {
+public:
+  static char ID;
+
+  AMDGPUExpandCondBarrier() : MachineFunctionPass(ID) {}
+
+  bool runOnMachineFunction(MachineFunction &MF) override;
+
+  StringRef getPassName() const override {
+    return "AMDGPU Expand Conditional Barriers";
+  }
+
+  void getAnalysisUsage(AnalysisUsage &AU) const override {
+    // We modify the CFG, so don't call setPreservesCFG().
----------------
arsenm wrote:

```suggestion
```

https://github.com/llvm/llvm-project/pull/171604