[clang] [Clang][WIP] Constant Expressions inside of gcc'asm strings (PR #131003)

[Erich Keane via cfe-commits]

================
@@ -17261,33 +17261,50 @@ void Sema::DiagnoseStaticAssertDetails(const Expr *E) 
{
   }
 }
 
-bool Sema::EvaluateStaticAssertMessageAsString(Expr *Message,
-                                               std::string &Result,
-                                               ASTContext &Ctx,
-                                               bool ErrorOnInvalidMessage) {
+template <typename ResultType>
+static bool EvaluateAsStringImpl(Sema &SemaRef, Expr *Message,
+                                 ResultType &Result, ASTContext &Ctx,
+                                 Sema::StringEvaluationContext EvalContext,
+                                 bool ErrorOnInvalidMessage) {
+
   assert(Message);
   assert(!Message->isTypeDependent() && !Message->isValueDependent() &&
          "can't evaluate a dependant static assert message");
 
   if (const auto *SL = dyn_cast<StringLiteral>(Message)) {
     assert(SL->isUnevaluated() && "expected an unevaluated string");
-    Result.assign(SL->getString().begin(), SL->getString().end());
+    if constexpr (std::is_same_v<APValue, ResultType>) {
+      Result =
+          APValue(APValue::UninitArray{}, SL->getLength(), SL->getLength());
+      const ConstantArrayType *CAT =
+          SemaRef.getASTContext().getAsConstantArrayType(SL->getType());
+      assert(CAT && "string literal isn't an array");
+      QualType CharType = CAT->getElementType();
+      llvm::APSInt Value(SemaRef.getASTContext().getTypeSize(CharType),
+                         CharType->isUnsignedIntegerType());
+      for (unsigned I = 0; I < SL->getLength(); I++) {
+        Value = SL->getCodeUnit(I);
+        Result.getArrayInitializedElt(I) = APValue(Value);
+      }
+    } else {
+      Result.assign(SL->getString().begin(), SL->getString().end());
+    }
     return true;
   }
 
   SourceLocation Loc = Message->getBeginLoc();
   QualType T = Message->getType().getNonReferenceType();
   auto *RD = T->getAsCXXRecordDecl();
   if (!RD) {
-    Diag(Loc, diag::err_static_assert_invalid_message);
+    SemaRef.Diag(Loc, diag::err_user_defined_msg_invalid) << EvalContext;
     return false;
   }
 
   auto FindMember = [&](StringRef Member, bool &Empty,
                         bool Diag = false) -> std::optional<LookupResult> {
-    DeclarationName DN = PP.getIdentifierInfo(Member);
-    LookupResult MemberLookup(*this, DN, Loc, Sema::LookupMemberName);
-    LookupQualifiedName(MemberLookup, RD);
+    DeclarationName DN = SemaRef.PP.getIdentifierInfo(Member);
+    LookupResult MemberLookup(SemaRef, DN, Loc, Sema::LookupMemberName);
+    SemaRef.LookupQualifiedName(MemberLookup, RD);
     Empty = MemberLookup.empty();
----------------
erichkeane wrote:

Whats hte point of `Empty` if we are returning an optional?

https://github.com/llvm/llvm-project/pull/131003
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