[llvm] [AMDGPU] Move kernarg preload logic to separate pass (PR #130434)

[Matt Arsenault via llvm-commits]

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@@ -0,0 +1,358 @@
+//===- AMDGPUPreloadKernelArguments.cpp - Preload Kernel Arguments --------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+//
+/// \file This pass preloads kernel arguments into user_data SGPRs before kernel
+/// execution begins. The number of registers available for preloading depends
+/// on the number of free user SGPRs, up to the hardware's maximum limit.
+/// Implicit arguments enabled in the kernel descriptor are allocated first,
+/// followed by SGPRs used for preloaded kernel arguments. (Reference:
+/// https://llvm.org/docs/AMDGPUUsage.html#initial-kernel-execution-state)
+/// Additionally, hidden kernel arguments may be preloaded, in which case they
+/// are appended to the kernel signature after explicit arguments. Preloaded
+/// arguments will be marked with `inreg`.
+//
+//===----------------------------------------------------------------------===//
+
+#include "AMDGPU.h"
+#include "AMDGPUTargetMachine.h"
+#include "llvm/Analysis/ValueTracking.h"
+#include "llvm/IR/Function.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/IR/IntrinsicsAMDGPU.h"
+#include "llvm/IR/Module.h"
+#include "llvm/IR/PassManager.h"
+#include "llvm/IR/Verifier.h"
+#include "llvm/Pass.h"
+
+#define DEBUG_TYPE "amdgpu-preload-kernel-arguments"
+
+using namespace llvm;
+
+static cl::opt<unsigned> KernargPreloadCount(
+    "amdgpu-kernarg-preload-count",
+    cl::desc("How many kernel arguments to preload onto SGPRs"), cl::init(0));
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arsenm wrote:

Can make this a pass parameter in a follow up 

https://github.com/llvm/llvm-project/pull/130434