[compiler-rt] [libfuzzer] Fix -runs=X flaky test (fuzzer-finalstats.test) (PR #96914)

[Mitch Phillips via llvm-commits]

https://github.com/hctim created https://github.com/llvm/llvm-project/pull/96914

Disables LSan in order to remove a 1% flake rate in this test.
There's some logic in LeakSanitizer and its integration into libFuzzer
that will disable LSan and re-run the input. This only happens when more
malloc()s are detected than free()s. Under high system load, this
appears to be possible as the "more mallocs than frees" is dependent on
walltime. In these instances, the number of runs ends up being `n + 1`,
which is undesirable.

>From c8852ca181b9844f13c298e3e7781ac146467c00 Mon Sep 17 00:00:00 2001
From: Mitch Phillips <mitchp at google.com>
Date: Thu, 27 Jun 2024 16:39:13 +0200
Subject: [PATCH] [libfuzzer] Fix -runs=X flaky test (fuzzer-finalstats.test)

Disables LSan in order to remove a 1% flake rate in this test.
There's some logic in LeakSanitizer and its integration into libFuzzer
that will disable LSan and re-run the input. This only happens when more
malloc()s are detected than free()s. Under high system load, this
appears to be possible as the "more mallocs than frees" is dependent on
walltime. In these instances, the number of runs ends up being `n + 1`,
which is undesirable.
---
 compiler-rt/test/fuzzer/fuzzer-finalstats.test | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/compiler-rt/test/fuzzer/fuzzer-finalstats.test b/compiler-rt/test/fuzzer/fuzzer-finalstats.test
index d8c991e308478..3a54b2ee003e5 100644
--- a/compiler-rt/test/fuzzer/fuzzer-finalstats.test
+++ b/compiler-rt/test/fuzzer/fuzzer-finalstats.test
@@ -1,12 +1,20 @@
 RUN: %cpp_compiler %S/SimpleTest.cpp -o %t-SimpleTest
-RUN: %run %t-SimpleTest -seed=1 -runs=77 -print_final_stats=1 2>&1 | FileCheck %s --check-prefix=FINAL_STATS
+
+// Note: `-detect_leaks=0` is required to prevent flakiness in this test.
+// There's some logic in LeakSanitizer and its integration into libFuzzer that
+// will disable LSan and re-run the input. This only happens when more malloc()s
+// are detected than free()s. Under high system load, this appears to be
+// possible as the "more mallocs than frees" is dependent on walltime. In these
+// instances, the number of runs ends up being `n + 1`, which is undesirable.
+
+RUN: %run %t-SimpleTest -seed=1 -runs=77 -print_final_stats=1 -detect_leaks=0 2>&1 | FileCheck %s --check-prefix=FINAL_STATS
 FINAL_STATS: stat::number_of_executed_units: 77
 FINAL_STATS: stat::average_exec_per_sec:     0
 FINAL_STATS: stat::new_units_added:
 FINAL_STATS: stat::slowest_unit_time_sec:    0
 FINAL_STATS: stat::peak_rss_mb:
 
-RUN: %run %t-SimpleTest %S/dict1.txt -runs=33 -print_final_stats=1 2>&1 | FileCheck %s --check-prefix=FINAL_STATS1
+RUN: %run %t-SimpleTest %S/dict1.txt -runs=33 -print_final_stats=1 -detect_leaks=0 2>&1 | FileCheck %s --check-prefix=FINAL_STATS1
 FINAL_STATS1: stat::number_of_executed_units: 33
 FINAL_STATS1: stat::peak_rss_mb: