[clang] Do not crash after suggesting typo correction to constexpr if…

… condition

In some cases non-null non-constant yet valid expression may reach point where
`ConditionResult` is created. For example, typo correction mechanism can return
such expression, so double check before evaluating it.

Fixes #61885

Reviewed By: tbaeder, aaron.ballman

Differential Revision: https://reviews.llvm.org/D148206

clang/docs/ReleaseNotes.rst

@@ -307,6 +307,8 @@ Bug Fixes in This Version
   bit-fields. This fixes:
   (`#61355 <https://github.com/llvm/llvm-project/issues/61335>`_) and
   (`#61417 <https://github.com/llvm/llvm-project/issues/61417>`_)
+- Fix crash after suggesting typo correction to constexpr if condition.
+  (`#61885 <https://github.com/llvm/llvm-project/issues/61885>`_)
 
 Bug Fixes to Compiler Builtins
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

clang/include/clang/Sema/Sema.h

@@ -12843,20 +12843,22 @@ class Sema final {
     Decl *ConditionVar;
     FullExprArg Condition;
     bool Invalid;
-    bool HasKnownValue;
-    bool KnownValue;
+    std::optional<bool> KnownValue;
 
     friend class Sema;
     ConditionResult(Sema &S, Decl *ConditionVar, FullExprArg Condition,
                     bool IsConstexpr)
-        : ConditionVar(ConditionVar), Condition(Condition), Invalid(false),
-          HasKnownValue(IsConstexpr && Condition.get() &&
-                        !Condition.get()->isValueDependent()),
-          KnownValue(HasKnownValue &&
-                     !!Condition.get()->EvaluateKnownConstInt(S.Context)) {}
+        : ConditionVar(ConditionVar), Condition(Condition), Invalid(false) {
+      if (IsConstexpr && Condition.get()) {
+        if (std::optional<llvm::APSInt> Val =
+                Condition.get()->getIntegerConstantExpr(S.Context)) {
+          KnownValue = !!(*Val);
+        }
+      }
+    }
     explicit ConditionResult(bool Invalid)
         : ConditionVar(nullptr), Condition(nullptr), Invalid(Invalid),
-          HasKnownValue(false), KnownValue(false) {}
+          KnownValue(std::nullopt) {}
 
   public:
     ConditionResult() : ConditionResult(false) {}
@@ -12865,11 +12867,7 @@ class Sema final {
       return std::make_pair(cast_or_null<VarDecl>(ConditionVar),
                             Condition.get());
     }
-    std::optional<bool> getKnownValue() const {
-      if (!HasKnownValue)
-        return std::nullopt;
-      return KnownValue;
-    }
+    std::optional<bool> getKnownValue() const { return KnownValue; }
   };
   static ConditionResult ConditionError() { return ConditionResult(true); }
 

clang/test/SemaCXX/invalid-if-constexpr.cpp

@@ -0,0 +1,14 @@
+// RUN: %clang_cc1 -verify -std=c++20 %s
+
+namespace GH61885 {
+void similar() { // expected-note {{'similar' declared here}}
+  if constexpr (similer<>) {} // expected-error {{use of undeclared identifier 'similer'; did you mean 'similar'?}}
+}
+void a() { if constexpr (__adl_swap<>) {}} // expected-error{{use of undeclared identifier '__adl_swap'; did you mean '__sync_swap'?}} \
+                                           // expected-note {{'__sync_swap' declared here}}
+
+int AA() { return true;} // expected-note {{'AA' declared here}}
+
+void b() { if constexpr (AAA<>) {}} // expected-error {{use of undeclared identifier 'AAA'; did you mean 'AA'?}}
+}
+