[clang] [llvm-profdata] Do not create numerical strings for MD5 function names read from a Sample Profile. (PR #66164)

[William Junda Huang via cfe-commits]

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@@ -0,0 +1,129 @@
+//===--- HashKeyMap.h - Wrapper for maps using hash value key ---*- 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
+///
+/// Defines HashKeyMap template.
+///
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_PROFILEDATA_HASHKEYMAP_H
+#define LLVM_PROFILEDATA_HASHKEYMAP_H
+
+#include "llvm/ADT/Hashing.h"
+#include <iterator>
+#include <utility>
+
+namespace llvm {
+
+namespace sampleprof {
+
+/// This class is a wrapper to associative container MapT<KeyT, ValueT> using
+/// the hash value of the original key as the new key. This greatly improves the
+/// performance of insert and query operations especially when hash values of
+/// keys are available a priori, and reduces memory usage if KeyT has a large
+/// size.
+/// All keys with the same hash value are considered equivalent (i.e. hash
+/// collision is silently ignored). Given such feature this class should only be
+/// used where it does not affect compilation correctness, for example, when
+/// loading a sample profile. The original key is not stored, so if the user
+/// needs to preserve it, it should be stored in the mapped type.
+/// Assuming the hashing algorithm is uniform, we use the formula
+/// 1 - Permute(n, k) / n ^ k where n is the universe size and k is number of
+/// elements chosen at random to calculate the probability of collision. With
+/// 1,000,000 entries the probability is negligible:
+/// 1 - (2^64)!/((2^64-1000000)!*(2^64)^1000000) ~= 3*10^-8.
+/// Source: https://en.wikipedia.org/wiki/Birthday_problem
+///
+/// \param MapT The underlying associative container type.
+/// \param KeyT The original key type, which requires the implementation of
+///   llvm::hash_value(KeyT).
+/// \param ValueT The original mapped type, which has the same requirement as
+///   the underlying container.
+/// \param MapTArgs Additional template parameters passed to the underlying
+///   container.
+template <template <typename, typename, typename...> typename MapT,
+          typename KeyT, typename ValueT, typename... MapTArgs>
+class HashKeyMap :
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huangjd wrote:

I moved it out from SampleProf.h because it is used outside of profile reader, now Trnasforms/IPO uses it several places 

https://github.com/llvm/llvm-project/pull/66164