[clang] [analyzer][Z3] Restore the original timeout of 15s (PR #118291)
Kristóf Umann via cfe-commits
cfe-commits at lists.llvm.org
Mon Dec 2 05:29:44 PST 2024
https://github.com/Szelethus created https://github.com/llvm/llvm-project/pull/118291
Discussion here:
https://discourse.llvm.org/t/analyzer-rfc-taming-z3-query-times/79520/15?u=szelethus
The original patch, #97298 introduced new timeouts backed by thorough testing and measurements to keep the running time of Z3 within reasonable limits. The measurements also showed that only certain reports and certain TUs were responsible for the poor performance of Z3 refutation.
Unfortunately, it seems like that on machines with different characteristics (slower machines) the current timeouts don't just axe 0.01% of reports, but many more as well. Considering that timeouts are inherently nondeterministic as a cutoff point, this lead reports sets being vastly different on the same projects with the same configuration. The discussion link shows that all configurations introduced in the patch with their default values lead to severa nondeterminism of the analyzer. As we, and others use the analyzer as a gating tool for PRs, we should revert to the original defaults.
We should respect that
* There are still parts of the analyzer that are either proven or suspected to contain nondeterministic code (like pointer sets),
* A 15s timeout is more likely to hit the same reports every time on a wider range of machines, but is still inherently nondeterministic, but an infinite timeout leads to the tool hanging,
* If you measure the performance of the analyzer on your machines, you can and should achieve some speedup with little or no observable nondeterminism.
>From 1fb92742a066444d4a074655704c8148ce1f8326 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Krist=C3=B3f=20Umann?= <dkszelethus at gmail.com>
Date: Mon, 2 Dec 2024 11:21:05 +0100
Subject: [PATCH] [analyzer][Z3] Restore the original timeout of 15s
Discussion here:
https://discourse.llvm.org/t/analyzer-rfc-taming-z3-query-times/79520/15?u=szelethus
The original patch, #97298 introduced new timeouts backed by thorough
testing and measurements to keep the running time of Z3 within
reasonable limits. The measurements also showed that only certain
reports and certain TUs were responsible for the poor performance of Z3
refutation.
Unfortunately, it seems like that on machines with different
characteristics (slower machines) the current timeouts don't just axe
0.01% of reports, but many more as well. Considering that timeouts are
inherently nondeterministic as a cutoff point, this lead reports sets
being vastly different on the same projects with the same configuration.
The discussion link shows that all configurations introduced in the
patch with their default values lead to severa nondeterminism of the
analyzer. As we, and others use the analyzer as a gating tool for PRs,
we should revert to the original defaults.
We should respect that
* There are still parts of the analyzer that are either proven or
suspected to contain nondeterministic code (like pointer sets),
* A 15s timeout is more likely to hit the same reports every time on a
wider range of machines, but is still inherently nondeterministic, but
an infinite timeout leads to the tool hanging,
* If you measure the performance of the analyzer on your machines, you
can and should achieve some speedup with little or no observable
nondeterminism.
---
.../clang/StaticAnalyzer/Core/AnalyzerOptions.def | 15 +++++++++------
clang/test/Analysis/analyzer-config.c | 6 +++---
.../StaticAnalyzer/Z3CrosscheckOracleTest.cpp | 14 +++++++-------
3 files changed, 19 insertions(+), 16 deletions(-)
diff --git a/clang/include/clang/StaticAnalyzer/Core/AnalyzerOptions.def b/clang/include/clang/StaticAnalyzer/Core/AnalyzerOptions.def
index 737bc8e86cfb6a..64fb11821a2656 100644
--- a/clang/include/clang/StaticAnalyzer/Core/AnalyzerOptions.def
+++ b/clang/include/clang/StaticAnalyzer/Core/AnalyzerOptions.def
@@ -189,20 +189,23 @@ ANALYZER_OPTION(
"crosscheck-with-z3-eqclass-timeout-threshold",
"Set a timeout for bug report equivalence classes in milliseconds. "
"If we exhaust this threshold, we will drop the bug report eqclass "
- "instead of doing more Z3 queries. Set 0 for no timeout.", 700)
+ "instead of doing more Z3 queries. On fast machines, 700 is a sane value. "
+ "Set 0 for no timeout.", 0)
ANALYZER_OPTION(
unsigned, Z3CrosscheckTimeoutThreshold,
"crosscheck-with-z3-timeout-threshold",
- "Set a timeout for individual Z3 queries in milliseconds. "
- "Set 0 for no timeout.", 300)
+ "Set a timeout for individual Z3 queries in milliseconds. On fast "
+ "machines, 400 is a sane value. "
+ "Set 0 for no timeout.", 15'000)
ANALYZER_OPTION(
unsigned, Z3CrosscheckRLimitThreshold,
"crosscheck-with-z3-rlimit-threshold",
- "Set the Z3 resource limit threshold. This sets a deterministic cutoff "
- "point for Z3 queries, as longer queries usually consume more resources. "
- "Set 0 for unlimited.", 400'000)
+ "Set the Z3 resource limit threshold. This sets a supposedly deterministic "
+ "cutoff point for Z3 queries, as longer queries usually consume more "
+ "resources. "
+ "Set 0 for unlimited.", 0)
ANALYZER_OPTION(bool, ShouldReportIssuesInMainSourceFile,
"report-in-main-source-file",
diff --git a/clang/test/Analysis/analyzer-config.c b/clang/test/Analysis/analyzer-config.c
index 8eb869bac46f8f..0f1314aae9db57 100644
--- a/clang/test/Analysis/analyzer-config.c
+++ b/clang/test/Analysis/analyzer-config.c
@@ -41,9 +41,9 @@
// CHECK-NEXT: cplusplus.Move:WarnOn = KnownsAndLocals
// CHECK-NEXT: cplusplus.SmartPtrModeling:ModelSmartPtrDereference = false
// CHECK-NEXT: crosscheck-with-z3 = false
-// CHECK-NEXT: crosscheck-with-z3-eqclass-timeout-threshold = 700
-// CHECK-NEXT: crosscheck-with-z3-rlimit-threshold = 400000
-// CHECK-NEXT: crosscheck-with-z3-timeout-threshold = 300
+// CHECK-NEXT: crosscheck-with-z3-eqclass-timeout-threshold = 0
+// CHECK-NEXT: crosscheck-with-z3-rlimit-threshold = 0
+// CHECK-NEXT: crosscheck-with-z3-timeout-threshold = 15000
// CHECK-NEXT: ctu-dir = ""
// CHECK-NEXT: ctu-import-cpp-threshold = 8
// CHECK-NEXT: ctu-import-threshold = 24
diff --git a/clang/unittests/StaticAnalyzer/Z3CrosscheckOracleTest.cpp b/clang/unittests/StaticAnalyzer/Z3CrosscheckOracleTest.cpp
index ef07e47ee911b2..a8cb2782c7b72f 100644
--- a/clang/unittests/StaticAnalyzer/Z3CrosscheckOracleTest.cpp
+++ b/clang/unittests/StaticAnalyzer/Z3CrosscheckOracleTest.cpp
@@ -38,8 +38,8 @@ static const AnalyzerOptions DefaultOpts = [] {
// Remember to update the tests in this file when these values change.
// Also update the doc comment of `interpretQueryResult`.
- assert(Config.Z3CrosscheckRLimitThreshold == 400'000);
- assert(Config.Z3CrosscheckTimeoutThreshold == 300_ms);
+ assert(Config.Z3CrosscheckRLimitThreshold == 0);
+ assert(Config.Z3CrosscheckTimeoutThreshold == 15'000_ms);
// Usually, when the timeout/rlimit threshold is reached, Z3 only slightly
// overshoots until it realizes that it overshoot and needs to back off.
// Consequently, the measured timeout should be fairly close to the threshold.
@@ -74,13 +74,13 @@ TEST_F(Z3CrosscheckOracleTest, SATWhenItGoesOverTime) {
}
TEST_F(Z3CrosscheckOracleTest, UNSATWhenItGoesOverTime) {
- ASSERT_EQ(RejectEQClass, interpretQueryResult({UNSAT, 310_ms, 1000_step}));
+ ASSERT_EQ(RejectReport, interpretQueryResult({UNSAT, 310_ms, 1000_step}));
}
TEST_F(Z3CrosscheckOracleTest, RejectsTimeout) {
ASSERT_EQ(RejectReport, interpretQueryResult({UNSAT, 25_ms, 1000_step}));
ASSERT_EQ(RejectReport, interpretQueryResult({UNSAT, 25_ms, 1000_step}));
- ASSERT_EQ(RejectEQClass, interpretQueryResult({UNDEF, 310_ms, 1000_step}));
+ ASSERT_EQ(RejectReport, interpretQueryResult({UNDEF, 310_ms, 1000_step}));
}
TEST_F(Z3CrosscheckOracleTest, RejectsUNSATs) {
@@ -97,7 +97,7 @@ TEST_F(Z3CrosscheckOracleTest, RejectEQClassIfSpendsTooMuchTotalTime) {
// Simulate long queries, that barely doesn't trigger the timeout.
ASSERT_EQ(RejectReport, interpretQueryResult({UNSAT, 290_ms, 1000_step}));
ASSERT_EQ(RejectReport, interpretQueryResult({UNSAT, 290_ms, 1000_step}));
- ASSERT_EQ(RejectEQClass, interpretQueryResult({UNSAT, 290_ms, 1000_step}));
+ ASSERT_EQ(RejectReport, interpretQueryResult({UNSAT, 290_ms, 1000_step}));
}
TEST_F(Z3CrosscheckOracleTest, SATWhenItSpendsTooMuchTotalTime) {
@@ -114,7 +114,7 @@ TEST_F(Z3CrosscheckOracleTest, RejectEQClassIfAttemptsManySmallQueries) {
ASSERT_EQ(RejectReport, interpretQueryResult({UNSAT, 20_ms, 1000_step}));
}
// Do one more to trigger the heuristic.
- ASSERT_EQ(RejectEQClass, interpretQueryResult({UNSAT, 1_ms, 1000_step}));
+ ASSERT_EQ(RejectReport, interpretQueryResult({UNSAT, 1_ms, 1000_step}));
}
TEST_F(Z3CrosscheckOracleTest, SATWhenIfAttemptsManySmallQueries) {
@@ -131,7 +131,7 @@ TEST_F(Z3CrosscheckOracleTest, SATWhenIfAttemptsManySmallQueries) {
TEST_F(Z3CrosscheckOracleTest, RejectEQClassIfExhaustsRLimit) {
ASSERT_EQ(RejectReport, interpretQueryResult({UNSAT, 25_ms, 1000_step}));
ASSERT_EQ(RejectReport, interpretQueryResult({UNSAT, 25_ms, 1000_step}));
- ASSERT_EQ(RejectEQClass, interpretQueryResult({UNDEF, 25_ms, 405'000_step}));
+ ASSERT_EQ(RejectReport, interpretQueryResult({UNDEF, 25_ms, 405'000_step}));
}
TEST_F(Z3CrosscheckOracleTest, SATWhenItExhaustsRLimit) {
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