[clang] [CIR] Upstream local initialization for VectorType (PR #138107)

[Henrich Lauko via cfe-commits]

================
@@ -1584,6 +1586,47 @@ mlir::Value ScalarExprEmitter::VisitMemberExpr(MemberExpr *e) {
   return emitLoadOfLValue(e);
 }
 
+mlir::Value ScalarExprEmitter::VisitInitListExpr(InitListExpr *e) {
+  const unsigned numInitElements = e->getNumInits();
+
+  if (e->hadArrayRangeDesignator()) {
+    cgf.cgm.errorNYI(e->getSourceRange(), "ArrayRangeDesignator");
+    return {};
+  }
+
+  if (numInitElements == 0) {
+    cgf.cgm.errorNYI(e->getSourceRange(), "InitListExpr with 0 init elements");
+    return {};
+  }
+
+  if (e->getType()->isVectorType()) {
+    const auto vectorType =
+        mlir::cast<cir::VectorType>(cgf.convertType(e->getType()));
+
+    SmallVector<mlir::Value, 16> elements;
+    for (Expr *init : e->inits()) {
+      elements.push_back(Visit(init));
+    }
+
+    // Zero-initialize any remaining values.
+    if (numInitElements < vectorType.getSize()) {
+      mlir::TypedAttr zeroInitAttr =
+          cgf.getBuilder().getZeroInitAttr(vectorType.getElementType());
+      cir::ConstantOp zeroValue = cgf.getBuilder().getConstant(
+          cgf.getLoc(e->getSourceRange()), zeroInitAttr);
----------------
xlauko wrote:

```suggestion
     cir::ConstantOp zeroValue = cgf.getBuilder().getNullValue(
         vectorType.getElementType(), cgf.getLoc(e->getSourceRange()));
```

https://github.com/llvm/llvm-project/pull/138107