[clang] [clang] Implement C2y stdc_load8_* endian-aware 8-bit load functions (PR #203666)

[Timm Baeder via cfe-commits]

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@@ -2103,6 +2103,91 @@ static bool isOneByteCharacterType(QualType T) {
   return T->isCharType() || T->isChar8Type();
 }
 
+static bool interp__builtin_load8(InterpState &S, CodePtr OpPC,
+                                  const InterpFrame *Frame,
+                                  const CallExpr *Call, bool IsBigEndian,
+                                  bool IsAligned) {
+  Pointer Ptr = S.Stk.pop<Pointer>();
+
+  if (Ptr.isZero()) {
+    S.FFDiag(S.Current->getSource(OpPC), diag::note_constexpr_access_null)
+        << AK_Read;
+    return false;
+  }
+
+  if (!isReadable(Ptr) && !Ptr.isOnePastEnd())
+    return false;
+
+  if (IsAligned) {
+    CharUnits RequiredAlign =
+        S.getASTContext().getTypeAlignInChars(Call->getType());
+    APValue AV = Ptr.toAPValue(S.getASTContext());
+    CharUnits BaseAlignment =
+        GetBaseAlignment(S.getASTContext(), AV.getLValueBase());
----------------
tbaederr wrote:

We basically already have an implementation of `getBaseAlignment()` in here: https://github.com/llvm/llvm-project/blob/cb25e7ca7cef9e84db077fe36f3d27b269394c65/clang/lib/AST/ByteCode/InterpBuiltin.cpp#L1424-L1428

https://github.com/llvm/llvm-project/pull/203666