[CIR] Backport Complex init with empty init list (#1668)

Backport support for Complex value initialization from the empty
InitList.

Backported from llvm/llvm-project#143192

Author: AmrDeveloper

clang/lib/CIR/CodeGen/CIRGenExprComplex.cpp

@@ -864,10 +864,16 @@ mlir::Value ComplexExprEmitter::VisitInitListExpr(InitListExpr *E) {
   if (E->getNumInits() == 1)
     return Visit(E->getInit(0));
 
-  // Empty init list initializes to null
   assert(E->getNumInits() == 0 && "Unexpected number of inits");
-  QualType Ty = E->getType()->castAs<ComplexType>()->getElementType();
-  return Builder.getZero(CGF.getLoc(E->getExprLoc()), CGF.convertType(Ty));
+  mlir::Location loc = CGF.getLoc(E->getExprLoc());
+  QualType complexElemTy =
+      E->getType()->castAs<clang::ComplexType>()->getElementType();
+  mlir::Type complexElemLLVMTy = CGF.convertType(complexElemTy);
+  mlir::TypedAttr defaultValue = Builder.getZeroInitAttr(complexElemLLVMTy);
+  auto complexTy = cir::ComplexType::get(complexElemLLVMTy);
+  auto complexAttr =
+      cir::ComplexAttr::get(complexTy, defaultValue, defaultValue);
+  return Builder.create<cir::ConstantOp>(loc, complexAttr);
 }
 
 mlir::Value CIRGenFunction::emitPromotedComplexExpr(const Expr *E,

clang/test/CIR/CodeGen/complex.c

@@ -335,3 +335,7 @@ void extract_imag() {
 // LLVM:   %{{.+}} = load double, ptr getelementptr inbounds nuw (i8, ptr @c, i64 8), align 8
 // LLVM:   %{{.+}} = load i32, ptr getelementptr inbounds nuw (i8, ptr @ci, i64 4), align 4
 // LLVM: }
+
+void complex_with_empty_init() { int _Complex c = {}; }
+
+// CHECK: {{.*}} = cir.const #cir.complex<#cir.int<0> : !s32i, #cir.int<0> : !s32i> : !cir.complex<!s32i>