[compiler-rt] [llvm] [tsan] Introduce Adaptive Delay Scheduling to TSAN (PR #178836)

[Chris Cotter via llvm-commits]

================
@@ -0,0 +1,131 @@
+//===-- tsan_fuzzing_scheduler.h --------------------------------*- 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
+//
+//===----------------------------------------------------------------------===//
+//
+// This file is a part of ThreadSanitizer (TSan), a race detector.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef TSAN_FUZZING_SCHEDULER_H
+#define TSAN_FUZZING_SCHEDULER_H
+
+#include "sanitizer_common/sanitizer_common.h"
+#include "sanitizer_common/sanitizer_internal_defs.h"
+
+namespace __tsan {
+
+// Fixed-point arithmetic type that mimics floating point operations
+class Percent {
+  using u32 = __sanitizer::u32;
+  using u64 = __sanitizer::u64;
+
+  u32 bp_{};  // basis points (0-10000 represents 0.0-1.0)
+  bool is_valid_{};
+
+  static constexpr u32 kBasisPointsPerUnit = 10000;
+
+  Percent(u32 bp, bool is_valid) : bp_(bp), is_valid_(is_valid) {}
+
+ public:
+  Percent() = default;
+  Percent(const Percent&) = default;
+  Percent& operator=(const Percent&) = default;
+  Percent(Percent&&) = default;
+  Percent& operator=(Percent&&) = default;
+
+  static Percent FromPct(u32 pct) { return Percent{pct * 100, true}; }
+  static Percent FromRatio(u64 numerator, u64 denominator) {
+    if (denominator == 0)
+      return Percent{0, false};
+    // Avoid overflow: scale down if needed
+    if (numerator > UINT64_MAX / kBasisPointsPerUnit) {
+      return Percent{(u32)((numerator / denominator) * kBasisPointsPerUnit),
+                     true};
+    }
+    return Percent{(u32)((numerator * kBasisPointsPerUnit) / denominator),
+                   true};
+  }
+
+  bool IsValid() const { return is_valid_; }
+
+  // Returns true with probability equal to the percentage.
+  bool RandomCheck(u32* seed) const {
+    return (Rand(seed) % kBasisPointsPerUnit) < bp_;
+  }
+
+  int GetPct() const { return bp_ / 100; }
+  int GetBasisPoints() const { return bp_; }
+
+  bool operator==(const Percent& other) const { return bp_ == other.bp_; }
+  bool operator!=(const Percent& other) const { return bp_ != other.bp_; }
+  bool operator<(const Percent& other) const { return bp_ < other.bp_; }
+  bool operator>(const Percent& other) const { return bp_ > other.bp_; }
+  bool operator<=(const Percent& other) const { return bp_ <= other.bp_; }
+  bool operator>=(const Percent& other) const { return bp_ >= other.bp_; }
+
+  Percent operator-(const Percent& other) const {
+    if (!is_valid_ || !other.is_valid_)
+      return Percent{0, false};
+    if (bp_ < other.bp_)
+      return Percent{0, false};
+    return Percent{bp_ - other.bp_, true};
+  }
+
+  Percent operator/(const Percent& other) const {
+    if (!is_valid_ || !other.is_valid_)
+      return Percent{0, false};
+    if (other.bp_ == 0)
+      return Percent{0, false};
+    return Percent{(bp_ * kBasisPointsPerUnit) / other.bp_, true};
+  }
+};
+
+struct IFuzzingScheduler {
----------------
ccotter wrote:

I removed any use of fuzzing and scheduler from the names/logic.

https://github.com/llvm/llvm-project/pull/178836