[clang] [CIR] Upstream SizeOf for VariableArrayType (PR #169993)

[Amr Hesham via cfe-commits]

================
@@ -2344,25 +2344,29 @@ mlir::Value ScalarExprEmitter::VisitUnaryExprOrTypeTraitExpr(
         } else {
           // C99 6.5.3.4p2: If the argument is an expression of type
           // VLA, it is evaluated.
-          cgf.getCIRGenModule().errorNYI(
-              e->getSourceRange(),
-              "sizeof operator for VariableArrayType & evaluateExtent "
-              "ignoredExpr",
-              e->getStmtClassName());
-          return {};
+          cgf.emitIgnoredExpr(e->getArgumentExpr());
         }
 
         // For _Countof, we just want to return the size of a single dimension.
         if (kind == UETT_CountOf)
           return cgf.getVLAElements1D(vat).numElts;
 
-        cgf.getCIRGenModule().errorNYI(
-            e->getSourceRange(),
-            "sizeof operator for VariableArrayType & evaluateExtent",
-            e->getStmtClassName());
-        return builder.getConstant(
-            loc, cir::IntAttr::get(cgf.cgm.uInt64Ty,
-                                   -llvm::APSInt(llvm::APInt(64, 1), true)));
+        // For sizeof and __datasizeof, we need to scale the number of elements
+        // by the size of the array element type.
+        auto vlaSize = cgf.getVLASize(vat);
----------------
AmrDeveloper wrote:

VlaSizePair is a struct inside CIRGenFunction to use the name we need to write it like

```
CIRGenFunction::VlaSizePair vlaSize = cgf.getVLASize(vat);
```

not sure if that's helpful 🤔 

https://github.com/llvm/llvm-project/pull/169993