[llvm] [AMDGPU] Introduce Next-Use Analysis for SSA-based Register Allocation (PR #156079)

[Nicolai Hähnle via llvm-commits]

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+//===-- AMDGPUNextUseAnalysis.h - Next Use Analysis ------------*- C++ -*-===//
+//
+// 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 file defines the Next Use Analysis for AMDGPU targets, which computes
+/// distances to next uses of virtual registers to guide register allocation
+/// and spilling decisions.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIB_TARGET_AMDGPU_NEXT_USE_ANALYSIS_H
+#define LLVM_LIB_TARGET_AMDGPU_NEXT_USE_ANALYSIS_H
+
+#include "llvm/ADT/DenseMap.h"
+#include "llvm/CodeGen/MachineLoopInfo.h"
+#include "llvm/CodeGen/SlotIndexes.h"
+
+#include "AMDGPUSSARAUtils.h"
+#include "GCNSubtarget.h"
+#include "SIRegisterInfo.h"
+#include "VRegMaskPair.h"
+
+#include <algorithm>
+#include <limits>
+#include <set>
+
+using namespace llvm;
+
+// namespace {
+
+// Helper function for rebasing successor distances into current block frame
+static inline int64_t rebaseFromSucc(int64_t SuccStored, unsigned SuccEntryOff,
+                                     int64_t EdgeWeight /*0 or LoopTag*/) {
+  // Move succ-relative value into "current block end" frame.
+  return (int64_t)SuccStored + (int64_t)SuccEntryOff + (int64_t)EdgeWeight;
+}
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nhaehnle wrote:

Why is this in a header file?

https://github.com/llvm/llvm-project/pull/156079