clang-misexpect: Profile Guided Validation of Performance Annotations in LLVM

This patch contains the basic functionality for reporting potentially
incorrect usage of __builtin_expect() by comparing the developer's
annotation against a collected PGO profile. A more detailed proposal and
discussion appears on the CFE-dev mailing list
(http://lists.llvm.org/pipermail/cfe-dev/2019-July/062971.html) and a
prototype of the initial frontend changes appear here in D65300

We revised the work in D65300 by moving the misexpect check into the
LLVM backend, and adding support for IR and sampling based profiles, in
addition to frontend instrumentation.

We add new misexpect metadata tags to those instructions directly
influenced by the llvm.expect intrinsic (branch, switch, and select)
when lowering the intrinsics. The misexpect metadata contains
information about the expected target of the intrinsic so that we can
check against the correct PGO counter when emitting diagnostics, and the
compiler's values for the LikelyBranchWeight and UnlikelyBranchWeight.
We use these branch weight values to determine when to emit the
diagnostic to the user.

A future patch should address the comment at the top of
LowerExpectIntrisic.cpp to hoist the LikelyBranchWeight and
UnlikelyBranchWeight values into a shared space that can be accessed
outside of the LowerExpectIntrinsic pass. Once that is done, the
misexpect metadata can be updated to be smaller.

In the long term, it is possible to reconstruct portions of the
misexpect metadata from the existing profile data. However, we have
avoided this to keep the code simple, and because some kind of metadata
tag will be required to identify which branch/switch/select instructions
are influenced by the use of llvm.expect

Patch By: paulkirth
Differential Revision: https://reviews.llvm.org/D66324

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@371584 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 185 insertions, 0 deletions

diff --git a/lib/profile/xxhash.c b/lib/profile/xxhash.c
new file mode 100644
index 000000000..e9dceed2c
--- /dev/null
+++ b/lib/profile/xxhash.c
@@ -0,0 +1,138 @@
+/*
+*  xxHash - Fast Hash algorithm
+*  Copyright (C) 2012-2016, Yann Collet
+*
+*  BSD 2-Clause License (http://www.opensource.org/licenses/bsd-license.php)
+*
+*  Redistribution and use in source and binary forms, with or without
+*  modification, are permitted provided that the following conditions are
+*  met:
+*
+*  * Redistributions of source code must retain the above copyright
+*  notice, this list of conditions and the following disclaimer.
+*  * Redistributions in binary form must reproduce the above
+*  copyright notice, this list of conditions and the following disclaimer
+*  in the documentation and/or other materials provided with the
+*  distribution.
+*
+*  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+*  "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+*  LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+*  A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+*  OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+*  SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+*  LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+*  DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+*  THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+*  (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+*  OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+*
+*  You can contact the author at :
+*  - xxHash homepage: http://www.xxhash.com
+*  - xxHash source repository : https://github.com/Cyan4973/xxHash
+*/
+
+/* based on revision d2df04efcbef7d7f6886d345861e5dfda4edacc1 Removed
+ * everything but a simple interface for computing XXh64. */
+
+#include "llvm/Support/xxhash.h"
+#include "llvm/Support/Endian.h"
+
+#include <stdlib.h>
+#include <string.h>
+
+using namespace llvm;
+using namespace support;
+
+static uint64_t rotl64(uint64_t X, size_t R) {
+  return (X << R) | (X >> (64 - R));
+}
+
+static const uint64_t PRIME64_1 = 11400714785074694791ULL;
+static const uint64_t PRIME64_2 = 14029467366897019727ULL;
+static const uint64_t PRIME64_3 = 1609587929392839161ULL;
+static const uint64_t PRIME64_4 = 9650029242287828579ULL;
+static const uint64_t PRIME64_5 = 2870177450012600261ULL;
+
+static uint64_t round(uint64_t Acc, uint64_t Input) {
+  Acc += Input * PRIME64_2;
+  Acc = rotl64(Acc, 31);
+  Acc *= PRIME64_1;
+  return Acc;
+}
+
+static uint64_t mergeRound(uint64_t Acc, uint64_t Val) {
+  Val = round(0, Val);
+  Acc ^= Val;
+  Acc = Acc * PRIME64_1 + PRIME64_4;
+  return Acc;
+}
+
+uint64_t llvm::xxHash64(StringRef Data) {
+  size_t Len = Data.size();
+  uint64_t Seed = 0;
+  const unsigned char *P = Data.bytes_begin();
+  const unsigned char *const BEnd = Data.bytes_end();
+  uint64_t H64;
+
+  if (Len >= 32) {
+    const unsigned char *const Limit = BEnd - 32;
+    uint64_t V1 = Seed + PRIME64_1 + PRIME64_2;
+    uint64_t V2 = Seed + PRIME64_2;
+    uint64_t V3 = Seed + 0;
+    uint64_t V4 = Seed - PRIME64_1;
+
+    do {
+      V1 = round(V1, endian::read64le(P));
+      P += 8;
+      V2 = round(V2, endian::read64le(P));
+      P += 8;
+      V3 = round(V3, endian::read64le(P));
+      P += 8;
+      V4 = round(V4, endian::read64le(P));
+      P += 8;
+    } while (P <= Limit);
+
+    H64 = rotl64(V1, 1) + rotl64(V2, 7) + rotl64(V3, 12) + rotl64(V4, 18);
+    H64 = mergeRound(H64, V1);
+    H64 = mergeRound(H64, V2);
+    H64 = mergeRound(H64, V3);
+    H64 = mergeRound(H64, V4);
+
+  } else {
+    H64 = Seed + PRIME64_5;
+  }
+
+  H64 += (uint64_t)Len;
+
+  while (P + 8 <= BEnd) {
+    uint64_t const K1 = round(0, endian::read64le(P));
+    H64 ^= K1;
+    H64 = rotl64(H64, 27) * PRIME64_1 + PRIME64_4;
+    P += 8;
+  }
+
+  if (P + 4 <= BEnd) {
+    H64 ^= (uint64_t)(endian::read32le(P)) * PRIME64_1;
+    H64 = rotl64(H64, 23) * PRIME64_2 + PRIME64_3;
+    P += 4;
+  }
+
+  while (P < BEnd) {
+    H64 ^= (*P) * PRIME64_5;
+    H64 = rotl64(H64, 11) * PRIME64_1;
+    P++;
+  }
+
+  H64 ^= H64 >> 33;
+  H64 *= PRIME64_2;
+  H64 ^= H64 >> 29;
+  H64 *= PRIME64_3;
+  H64 ^= H64 >> 32;
+
+  return H64;
+}
+
+uint64_t llvm::xxHash64(ArrayRef<uint8_t> Data) {
+  return xxHash64({(const char *)Data.data(), Data.size()});
+}
diff --git a/lib/profile/xxhash.h b/lib/profile/xxhash.h
new file mode 100644
index 000000000..85fc66606
--- /dev/null
+++ b/lib/profile/xxhash.h
@@ -0,0 +1,47 @@
+/*
+   xxHash - Extremely Fast Hash algorithm
+   Header File
+   Copyright (C) 2012-2016, Yann Collet.
+
+   BSD 2-Clause License (http://www.opensource.org/licenses/bsd-license.php)
+
+   Redistribution and use in source and binary forms, with or without
+   modification, are permitted provided that the following conditions are
+   met:
+
+       * Redistributions of source code must retain the above copyright
+   notice, this list of conditions and the following disclaimer.
+       * Redistributions in binary form must reproduce the above
+   copyright notice, this list of conditions and the following disclaimer
+   in the documentation and/or other materials provided with the
+   distribution.
+
+   THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+   "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+   LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+   A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+   OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+   SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+   LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+   DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+   THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+   (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+   OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+   You can contact the author at :
+   - xxHash source repository : https://github.com/Cyan4973/xxHash
+*/
+
+/* based on revision d2df04efcbef7d7f6886d345861e5dfda4edacc1 Removed
+ * everything but a simple interface for computing XXh64. */
+
+#ifndef PROFILE_XXHASH_H_
+#define PROFILE_XXHASH_H_
+
+#include "llvm/ADT/ArrayRef.h"
+#include "llvm/ADT/StringRef.h"
+
+uint64_t xxHash64(llvm::StringRef Data);
+uint64_t xxHash64(llvm::ArrayRef<uint8_t> Data);
+
+#endif