[llvm] [AMDGPU] Add AMDGPU-specific module splitting (PR #89245)

[Matt Arsenault via llvm-commits]

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+//===- AMDGPUSplitModule.cpp ----------------------------------------------===//
+//
+// 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 Implements a module splitting algorithm designed to support the
+/// FullLTO --lto-partitions option for parallel codegen. This is completely
+/// different from the common SplitModule pass, as this system is designed with
+/// AMDGPU in mind.
+///
+/// The basic idea of this module splitting implementation is the same as
+/// SplitModule: load-balance the module's functions across a set of N
+/// partitions to allow parallel codegen. However, it does it very
+/// differently than the target-agnostic variant:
+///   - Kernels are used as the module's "roots".
+///     They're known entry points on AMDGPU, and everything else is often
+///     internal only.
+///   - Each kernel has a set of dependencies, and when a kernel and its
+///     dependencies is considered "big", we try to put it in a partition where
+///     most dependencies are already imported, to avoid duplicating large
+///     amounts of code.
+///   - There's special care for indirect calls in order to ensure
+///     AMDGPUResourceUsageAnalysis can work correctly.
+///
+/// This file also includes a more elaborate logging system to enable
+/// users to easily generate logs that (if desired) do not include any value
+/// names, in order to not leak information about the source file.
+/// Such logs are very helpful to understand and fix potential issues with
+/// module splitting.
+//
+//===----------------------------------------------------------------------===//
+
+#include "AMDGPUSplitModule.h"
+#include "AMDGPUTargetMachine.h"
+#include "Utils/AMDGPUBaseInfo.h"
+#include "llvm/ADT/DenseMap.h"
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/ADT/StringExtras.h"
+#include "llvm/ADT/StringRef.h"
+#include "llvm/Analysis/CallGraph.h"
+#include "llvm/Analysis/TargetTransformInfo.h"
+#include "llvm/IR/Function.h"
+#include "llvm/IR/Instruction.h"
+#include "llvm/IR/Module.h"
+#include "llvm/IR/User.h"
+#include "llvm/IR/Value.h"
+#include "llvm/Support/Casting.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/FileSystem.h"
+#include "llvm/Support/Process.h"
+#include "llvm/Support/SHA256.h"
+#include "llvm/Support/raw_ostream.h"
+#include "llvm/Transforms/Utils/Cloning.h"
+#include <algorithm>
+#include <cassert>
+#include <iterator>
+#include <memory>
+#include <utility>
+#include <vector>
+
+using namespace llvm;
+
+#define DEBUG_TYPE "amdgpu-split-module"
+
+namespace {
+
+static cl::opt<float> LargeKernelFactor(
+    "amdgpu-module-splitting-large-kernel-threshold", cl::init(2.0), cl::Hidden,
+    cl::desc(
+        "consider a kernel as large and needing special treatment when it "
+        "exceeds the average cost of a partition by this factor; e;g. 2.0 "
+        "means if the kernel and its dependencies is 2 times bigger than "
+        "an average partition; 0 disables large kernels handling entirely"));
+
+static cl::opt<float> LargeKernelOverlapForMerge(
+    "amdgpu-module-splitting-large-kernel-merge-overlap", cl::init(0.8),
----------------
arsenm wrote:

```suggestion
    "amdgpu-module-splitting-large-kernel-merge-overlap", cl::init(0.8f),
```

https://github.com/llvm/llvm-project/pull/89245