[clang] [clang] Remember which concept-ids are known to be satisfied (PR #227398)

[Shafik Yaghmour via cfe-commits]

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@@ -1131,11 +1153,11 @@ ExprResult ConstraintSatisfactionChecker::Evaluate(
   // ConceptIdConstraint is only relevant for diagnostics,
   // so if the normalized constraint is satisfied, we should not
   // substitute into the constraint.
-  if (Satisfaction.IsSatisfied)
+  if (Satisfaction.IsSatisfied) {
+    if (!BuildExpression && !Satisfaction.ContainsErrors)
+      PMCache.cacheSatisfied();
     return E;
-
-  ParameterMappingInstantiationCache PMCache(
-      *this, Constraint, MLTAL, getOuterPackIndex(Constraint), Size);
+  }
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shafik wrote:

This seems worth adding a comment for.

https://github.com/llvm/llvm-project/pull/227398