[clang] e098135 - [clang][dataflow] Move expensive solver asserts under EXPENSIVE_CHECKS (#205715)

[via cfe-commits]

Author: Zeyi Xu
Date: 2026-06-25T21:08:26+08:00
New Revision: e0981358efdf3c630d1921fd81ba55af5e406364

URL: https://github.com/llvm/llvm-project/commit/e0981358efdf3c630d1921fd81ba55af5e406364
DIFF: https://github.com/llvm/llvm-project/commit/e0981358efdf3c630d1921fd81ba55af5e406364.diff

LOG: [clang][dataflow] Move expensive solver asserts under EXPENSIVE_CHECKS (#205715)

The watched-literal solver has a few invariant checks that run on every
solver iteration in assertion builds. Some of these checks rebuild and
iterate over the watched-literal state. This overhead is usually hidden,
but it becomes dominant for large flow-sensitive analyses.

While testing clang-tidy's `unchecked-optional-access` check on real
world projects (in this case, LLVM itself), we found there are a few
extreme slow analyses caused by this overhead.

| Time    | File                                                |
|---------|-----------------------------------------------------|
| 8235.7s | llvm-project/clang/utils/TableGen/RISCVVEmitter.cpp |
| 8197.2s | llvm-project/clang/lib/Driver/Multilib.cpp          |

(Ran on a machine with Icelake 32cores + 128gb memory)

After moving these asserts to `EXPENSIVE_CHECKS`, the same files
complete in about 14.2 seconds and 12.2 seconds locally. That is roughly
a 580x improvement for `RISCVVEmitter.cpp` and a 673x improvement for
`Multilib.cpp`.

This can also affect clang-tidy pre-merge CI, because the pre-merge
configuration uses an assertions build and enables
`bugprone-unchecked-optional-access`.

Given this scale of improvement, I think these invariant checks are
better suited for `EXPENSIVE_CHECKS`. They remain available in dedicated
expensive-check builds, while avoiding a very large cost in regular
release+assertions builds.

Closes https://github.com/llvm/llvm-project/issues/205713

Added: 
    

Modified: 
    clang/lib/Analysis/FlowSensitive/WatchedLiteralsSolver.cpp

Removed: 
    


################################################################################
diff  --git a/clang/lib/Analysis/FlowSensitive/WatchedLiteralsSolver.cpp b/clang/lib/Analysis/FlowSensitive/WatchedLiteralsSolver.cpp
index a39f0e0b29ad1..98109faff222a 100644
--- a/clang/lib/Analysis/FlowSensitive/WatchedLiteralsSolver.cpp
+++ b/clang/lib/Analysis/FlowSensitive/WatchedLiteralsSolver.cpp
@@ -162,9 +162,11 @@ class WatchedLiteralsSolverImpl {
       // FIXME: Consider replacing these with test cases that fail if the any
       // of the invariants is broken. That might not be easy due to the
       // transformations performed by `buildCNF`.
+#ifdef EXPENSIVE_CHECKS
       assert(activeVarsAreUnassigned());
       assert(activeVarsFormWatchedLiterals());
       assert(unassignedVarsFormingWatchedLiteralsAreActive());
+#endif
 
       const Variable ActiveVar = ActiveVars[I];