[llvm] [ctx_profile] Profile reader and writer (PR #91859)

[Snehasish Kumar via llvm-commits]

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@@ -0,0 +1,91 @@
+//===--- PGOCtxProfReader.h - Contextual profile reader ---------*- 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
+///
+/// Reader for contextual iFDO profile, which comes in bitstream format.
+///
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_PROFILEDATA_CTXINSTRPROFILEREADER_H
+#define LLVM_PROFILEDATA_CTXINSTRPROFILEREADER_H
+
+#include "llvm/ADT/DenseSet.h"
+#include "llvm/Bitstream/BitstreamReader.h"
+#include "llvm/IR/GlobalValue.h"
+#include "llvm/ProfileData/PGOCtxProfWriter.h"
+#include "llvm/Support/Error.h"
+#include <map>
+#include <vector>
+
+namespace llvm {
+/// The loaded contextual profile, suitable for mutation during IPO passes. We
+/// generally expect a fraction of counters and of callsites to be populated.
+/// We continue to model counters as vectors, but callsites are modeled as a map
+/// of a map. The expectation is that, typically, there is a small number of
+/// indirect targets (usually, 1 for direct calls); but potentially a large
+/// number of callsites, and, as inlining progresses, the callsite count of a
+/// caller will grow.
+class PGOContextualProfile final {
+public:
+  using CallTargetMapTy = std::map<GlobalValue::GUID, PGOContextualProfile>;
+  using CallsiteMapTy = DenseMap<uint32_t, CallTargetMapTy>;
+
+private:
+  friend class PGOCtxProfileReader;
+  GlobalValue::GUID GUID = 0;
+  SmallVector<uint64_t, 16> Counters;
+  CallsiteMapTy Callsites;
+
+  PGOContextualProfile(GlobalValue::GUID G,
+                       SmallVectorImpl<uint64_t> &&Counters)
+      : GUID(G), Counters(std::move(Counters)) {}
+
+  Expected<PGOContextualProfile &>
+  getOrEmplace(uint32_t Index, GlobalValue::GUID G,
+               SmallVectorImpl<uint64_t> &&Counters);
+
+public:
+  PGOContextualProfile(const PGOContextualProfile &) = delete;
+  PGOContextualProfile &operator=(const PGOContextualProfile &) = delete;
+  PGOContextualProfile(PGOContextualProfile &&) = default;
+  PGOContextualProfile &operator=(PGOContextualProfile &&) = default;
+
+  GlobalValue::GUID guid() const { return GUID; }
+  const SmallVectorImpl<uint64_t> &counters() const { return Counters; }
+  const CallsiteMapTy &callsites() const { return Callsites; }
+  CallsiteMapTy &callsites() { return Callsites; }
+
+  bool hasCallsite(uint32_t I) const {
+    return Callsites.find(I) != Callsites.end();
+  }
+
+  const CallTargetMapTy &callsite(uint32_t I) const {
+    return Callsites.find(I)->second;
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snehasish wrote:

Maybe add an `assert(hasCallsite(I) && "Callsite not found");` too?

https://github.com/llvm/llvm-project/pull/91859