[clang] [LifetimeSafety] Add language option for experimental lifetime safety (PR #149592)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: Utkarsh Saxena (usx95)

<details>
<summary>Changes</summary>

Add a language option flag for experimental lifetime safety analysis in C++.

This change provides a language option to control the experimental lifetime safety analysis feature, making it more explicit and easier to enable/disable. Previously, the feature was controlled indirectly through a diagnostic warning flag, which we do not want to accidentally enable with `-Weverything` (atm)!

### Changes:

- Added a new language option `EnableLifetimeSafety` in `LangOptions.def` for experimental lifetime safety analysis in C++
- Added corresponding driver options `-fexperimental-lifetime-safety` and `-fno-experimental-lifetime-safety` in `Options.td`
- Modified `AnalysisBasedWarnings.cpp` to use the new language option flag instead of checking if a specific diagnostic is ignored
- Updated a test case to use the new flag instead of relying on the warning flag alone



---
Full diff: https://github.com/llvm/llvm-project/pull/149592.diff


4 Files Affected:

- (modified) clang/include/clang/Basic/LangOptions.def (+2) 
- (modified) clang/include/clang/Driver/Options.td (+8) 
- (modified) clang/lib/Sema/AnalysisBasedWarnings.cpp (+1-2) 
- (modified) clang/test/Sema/warn-lifetime-safety-dataflow.cpp (+1-1) 


``````````diff
diff --git a/clang/include/clang/Basic/LangOptions.def b/clang/include/clang/Basic/LangOptions.def
index 6ac8d496f1494..08d98a77e0252 100644
--- a/clang/include/clang/Basic/LangOptions.def
+++ b/clang/include/clang/Basic/LangOptions.def
@@ -491,6 +491,8 @@ LANGOPT(CheckConstexprFunctionBodies, 1, 1, Benign,
 
 LANGOPT(BoundsSafety, 1, 0, NotCompatible, "Bounds safety extension for C")
 
+LANGOPT(EnableLifetimeSafety, 1, 0, NotCompatible, "Experimental lifetime safety analysis for C++")
+
 LANGOPT(PreserveVec3Type, 1, 0, NotCompatible, "Preserve 3-component vector type")
 
 #undef LANGOPT
diff --git a/clang/include/clang/Driver/Options.td b/clang/include/clang/Driver/Options.td
index a8c1b5dd8ab3b..8e6fd5f99c503 100644
--- a/clang/include/clang/Driver/Options.td
+++ b/clang/include/clang/Driver/Options.td
@@ -1917,6 +1917,14 @@ defm bounds_safety : BoolFOption<
   BothFlags<[], [CC1Option],
           " experimental bounds safety extension for C">>;
 
+defm lifetime_safety : BoolFOption<
+  "experimental-lifetime-safety",
+  LangOpts<"EnableLifetimeSafety">, DefaultFalse,
+  PosFlag<SetTrue, [], [CC1Option], "Enable">,
+  NegFlag<SetFalse, [], [CC1Option], "Disable">,
+  BothFlags<[], [CC1Option],
+          " experimental lifetime safety for C++">>;
+
 defm addrsig : BoolFOption<"addrsig",
   CodeGenOpts<"Addrsig">, DefaultFalse,
   PosFlag<SetTrue, [], [ClangOption, CC1Option], "Emit">,
diff --git a/clang/lib/Sema/AnalysisBasedWarnings.cpp b/clang/lib/Sema/AnalysisBasedWarnings.cpp
index 5eba024e83634..20dfe19a8f968 100644
--- a/clang/lib/Sema/AnalysisBasedWarnings.cpp
+++ b/clang/lib/Sema/AnalysisBasedWarnings.cpp
@@ -2902,8 +2902,7 @@ void clang::sema::AnalysisBasedWarnings::IssueWarnings(
       .setAlwaysAdd(Stmt::UnaryOperatorClass);
   }
 
-  bool EnableLifetimeSafetyAnalysis = !Diags.isIgnored(
-      diag::warn_experimental_lifetime_safety_dummy_warning, D->getBeginLoc());
+  bool EnableLifetimeSafetyAnalysis = S.getLangOpts().EnableLifetimeSafety;
   // Install the logical handler.
   std::optional<LogicalErrorHandler> LEH;
   if (LogicalErrorHandler::hasActiveDiagnostics(Diags, D->getBeginLoc())) {
diff --git a/clang/test/Sema/warn-lifetime-safety-dataflow.cpp b/clang/test/Sema/warn-lifetime-safety-dataflow.cpp
index 0e98904ade86a..1c7ea5b2adfaf 100644
--- a/clang/test/Sema/warn-lifetime-safety-dataflow.cpp
+++ b/clang/test/Sema/warn-lifetime-safety-dataflow.cpp
@@ -1,4 +1,4 @@
-// RUN: %clang_cc1 -mllvm -debug-only=LifetimeFacts,LifetimeLoanPropagation -Wexperimental-lifetime-safety %s 2>&1 | FileCheck %s
+// RUN: %clang_cc1 -fexperimental-lifetime-safety -mllvm -debug-only=LifetimeFacts,LifetimeLoanPropagation -Wexperimental-lifetime-safety %s 2>&1 | FileCheck %s
 // REQUIRES: asserts
 
 struct MyObj {

``````````

</details>


https://github.com/llvm/llvm-project/pull/149592