[clang][ExprConst] Handle dependent switch case statements (#166533)

By rejecting them.

Fixes https://github.com/llvm/llvm-project/issues/165555

clang/lib/AST/ByteCode/Compiler.cpp

diff --git a/clang/lib/AST/ByteCode/Compiler.cpp b/clang/lib/AST/ByteCode/Compiler.cpp
index 4e63400..84f7e62 100644
--- a/clang/lib/AST/ByteCode/Compiler.cpp
+++ b/clang/lib/AST/ByteCode/Compiler.cpp
@@ -6007,6 +6007,8 @@
       CaseLabels[SC] = this->getLabel();
 
       const Expr *Value = CS->getLHS();
+      if (Value->isValueDependent())
+        return false;
       PrimType ValueT = this->classifyPrim(Value->getType());
 
       // Compare the case statement's value to the switch condition.

clang/lib/AST/ExprConstant.cpp

diff --git a/clang/lib/AST/ExprConstant.cpp b/clang/lib/AST/ExprConstant.cpp
index 8fab6ef..193f87c 100644
--- a/clang/lib/AST/ExprConstant.cpp
+++ b/clang/lib/AST/ExprConstant.cpp
@@ -5452,10 +5452,13 @@
     }
 
     const CaseStmt *CS = cast<CaseStmt>(SC);
-    APSInt LHS = CS->getLHS()->EvaluateKnownConstInt(Info.Ctx);
-    APSInt RHS = CS->getRHS() ? CS->getRHS()->EvaluateKnownConstInt(Info.Ctx)
-                              : LHS;
-    if (LHS <= Value && Value <= RHS) {
+    const Expr *LHS = CS->getLHS();
+    const Expr *RHS = CS->getRHS();
+    if (LHS->isValueDependent() || (RHS && RHS->isValueDependent()))
+      return ESR_Failed;
+    APSInt LHSValue = LHS->EvaluateKnownConstInt(Info.Ctx);
+    APSInt RHSValue = RHS ? RHS->EvaluateKnownConstInt(Info.Ctx) : LHSValue;
+    if (LHSValue <= Value && Value <= RHSValue) {
       Found = SC;
       break;
     }

clang/test/SemaCXX/dependent-switch-case.cpp

diff --git a/clang/test/SemaCXX/dependent-switch-case.cpp b/clang/test/SemaCXX/dependent-switch-case.cpp
new file mode 100644
index 0000000..bbeab3a
--- /dev/null
+++ b/clang/test/SemaCXX/dependent-switch-case.cpp
@@ -0,0 +1,6 @@
+// RUN: %clang_cc1 -std=c++20 %s -verify
+// RUN: %clang_cc1 -std=c++20 %s -verify -fexperimental-new-constant-interpreter
+
+constexpr bool e(int){switch(0)0=0:return t(;} // expected-error {{expression is not assignable}} \
+                                               // expected-error {{expected 'case' keyword before expression}} \
+                                               // expected-error {{expected expression}}