[Lldb-commits] [lldb] [lldb] Add interface to check if UserExpression::Parse() is cacheable (PR #66826)

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llvmbot wrote:


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@llvm/pr-subscribers-lldb

Author: Augusto Noronha (augusto2112)

<details>
<summary>Changes</summary>

When setting conditional breakpoints, we currently assume that a call to UserExpression::Parse() can be cached and resued multiple times. This may not be true for every user expression. Add a new method so subclasses of UserExpression can customize if they are parseable or not.

---
Full diff: https://github.com/llvm/llvm-project/pull/66826.diff


2 Files Affected:

- (modified) lldb/include/lldb/Expression/UserExpression.h (+8) 
- (modified) lldb/source/Breakpoint/BreakpointLocation.cpp (+1) 


``````````diff
diff --git a/lldb/include/lldb/Expression/UserExpression.h b/lldb/include/lldb/Expression/UserExpression.h
index df7a76664f6d5b6..b6cfeec7e899330 100644
--- a/lldb/include/lldb/Expression/UserExpression.h
+++ b/lldb/include/lldb/Expression/UserExpression.h
@@ -192,6 +192,14 @@ class UserExpression : public Expression {
   /// expression.  Text() should contain the definition of this function.
   const char *FunctionName() override { return "$__lldb_expr"; }
 
+  /// Returns whether the call to Parse on this user expression is cacheable.
+  /// This function exists to provide an escape hatch for supporting languages
+  /// where parsing an expression in the exact same context is unsafe. For
+  /// example, languages where generic functions aren't monomorphized, but
+  /// implement some other mechanism to represent generic values, may be unsafe
+  /// to cache, as the concrete type substitution may be different in every
+  /// expression evaluation.
+  virtual bool IsParseCacheable() { return true; }
   /// Return the language that should be used when parsing.  To use the
   /// default, return eLanguageTypeUnknown.
   lldb::LanguageType Language() const override { return m_language; }
diff --git a/lldb/source/Breakpoint/BreakpointLocation.cpp b/lldb/source/Breakpoint/BreakpointLocation.cpp
index 0fcefe5c63be749..2d2e00883f32ef7 100644
--- a/lldb/source/Breakpoint/BreakpointLocation.cpp
+++ b/lldb/source/Breakpoint/BreakpointLocation.cpp
@@ -250,6 +250,7 @@ bool BreakpointLocation::ConditionSaysStop(ExecutionContext &exe_ctx,
   DiagnosticManager diagnostics;
 
   if (condition_hash != m_condition_hash || !m_user_expression_sp ||
+      !m_user_expression_sp->IsParseCacheable() ||
       !m_user_expression_sp->MatchesContext(exe_ctx)) {
     LanguageType language = eLanguageTypeUnknown;
     // See if we can figure out the language from the frame, otherwise use the

``````````

</details>


https://github.com/llvm/llvm-project/pull/66826