[clang] e7b827e - Add a FIXME comment; NFC

[Aaron Ballman via cfe-commits]

Author: Aaron Ballman
Date: 2023-10-18T12:16:33-04:00
New Revision: e7b827e11bd36cb7056538d05761039af9ced60d

URL: https://github.com/llvm/llvm-project/commit/e7b827e11bd36cb7056538d05761039af9ced60d
DIFF: https://github.com/llvm/llvm-project/commit/e7b827e11bd36cb7056538d05761039af9ced60d.diff

LOG: Add a FIXME comment; NFC

The constant expression engines use a list of note diagnostics to
report back whether an evaluation is a valid constant expression or
not. This requires the engines to generate those note diagnostics, and
that can be expensive in cases where we're converting an APValue to a
string as a streamed argument to the note. If we're going to display
the note, then that expense is warranted. However, there are operations
looking for a yes/no answer to whether something is a constant
expression and won't display the diagnostics at all. Those uses are
paying an expense they shouldn't have to.

Added: 
    

Modified: 
    clang/include/clang/AST/Expr.h

Removed: 
    


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diff  --git a/clang/include/clang/AST/Expr.h b/clang/include/clang/AST/Expr.h
index b69c616b0090365..638f886edd095f1 100644
--- a/clang/include/clang/AST/Expr.h
+++ b/clang/include/clang/AST/Expr.h
@@ -607,6 +607,13 @@ class Expr : public ValueStmt {
     /// foldable. If the expression is foldable, but not a constant expression,
     /// the notes will describes why it isn't a constant expression. If the
     /// expression *is* a constant expression, no notes will be produced.
+    ///
+    /// FIXME: this causes significant performance concerns and should be
+    /// refactored at some point. Not all evaluations of the constant
+    /// expression interpreter will display the given diagnostics, this means
+    /// those kinds of uses are paying the expense of generating a diagnostic
+    /// (which may include expensive operations like converting APValue objects
+    /// to a string representation).
     SmallVectorImpl<PartialDiagnosticAt> *Diag = nullptr;
 
     EvalStatus() = default;