[clang] [CIR][CodeGen] Support DesignatedInitUpdateExpr in constant emission (PR #194238)

[Andy Kaylor via cfe-commits]

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@@ -399,9 +472,43 @@ ConstantAggregateBuilder::buildFrom(CIRGenModule &cgm, ArrayRef<Element> elems,
 
   // If we want an array type, see if all the elements are the same type and
   // appropriately spaced.
-  if (mlir::isa<cir::ArrayType>(desiredTy)) {
-    cgm.errorNYI("array aggregate constants");
-    return {};
+  if (auto arrTy = mlir::dyn_cast<cir::ArrayType>(desiredTy)) {
+    mlir::Type eltTy = arrTy.getElementType();
+    uint64_t numElements = arrTy.getSize();
+    CharUnits eltSize = utils.getSize(eltTy);
+
+    // Check if all elements have the correct type and are at stride offsets.
+    SmallVector<mlir::Attribute> arrayElts(numElements);
+    bool canBuildArray = true;
+
+    for (const auto &[element, offset] : elems) {
+      CharUnits relOffset = offset - startOffset;
+      if (relOffset % eltSize != CharUnits::Zero() ||
+          element.getType() != eltTy) {
+        canBuildArray = false;
+        break;
+      }
+      uint64_t idx = relOffset / eltSize;
+      if (idx >= numElements) {
+        canBuildArray = false;
+        break;
+      }
+      arrayElts[idx] = element;
+    }
+
+    if (canBuildArray) {
+      // Fill gaps with zero.
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andykaylor wrote:

Can you use `emitArrayConstant` here as classic codegen does?

https://github.com/llvm/llvm-project/pull/194238