From 698f10bd8926187063f9b7df84f582a650a453f4 Mon Sep 17 00:00:00 2001
From: Fuad Hasan <fuad.cs22@gmail.com>
Date: Tue, 28 Apr 2026 01:09:14 +0600
Subject: [PATCH] llvm: lower array params as aggregate byval

---
 internal/backend/llvm/link.go       |  2 ++
 internal/backend/llvm/llvm.go       |  5 ++++-
 internal/backend/llvm/lower_test.go | 24 ++++++++++++++++++++++++
 3 files changed, 30 insertions(+), 1 deletion(-)

diff --git a/internal/backend/llvm/link.go b/internal/backend/llvm/link.go
index c4b22690..b65d565c 100644
--- a/internal/backend/llvm/link.go
+++ b/internal/backend/llvm/link.go
@@ -110,6 +110,8 @@ func FunctionReturnIsScalar(fn *mir.Function) bool {
 // Returns an error for aggregate (named struct) types.
 func llvmBaseType(typ typeinfo.Type) (string, error) {
 	switch base := backend.UnwrapNamed(typ).(type) {
+	case *typeinfo.ApproxType:
+		return llvmBaseType(base.Inner)
 	case *typeinfo.BuiltinType:
 		if _, bits, ok := tokens.ParseIntegerBuiltin(base.Name); ok {
 			return fmt.Sprintf("i%d", bits), nil
diff --git a/internal/backend/llvm/llvm.go b/internal/backend/llvm/llvm.go
index 5de0917c..cf5b99a0 100644
--- a/internal/backend/llvm/llvm.go
+++ b/internal/backend/llvm/llvm.go
@@ -5590,7 +5590,10 @@ func llvmFieldType(state *moduleState, typ typeinfo.Type) (string, error) {
 
 // llvmABITypeName returns the LLVM type name for function signatures, calls, globals.
 func llvmABITypeName(state *moduleState, typ typeinfo.Type) (string, error) {
-	if _, ok := backend.UnwrapNamed(typ).(*typeinfo.TupleType); ok {
+	switch t := backend.UnwrapNamed(typ).(type) {
+	case *typeinfo.ApproxType:
+		return llvmABITypeName(state, t.Inner)
+	case *typeinfo.TupleType, *typeinfo.ArrayType:
 		size, _, err := backend.AggregateSizeAlign(aggregateLayoutContext(state), typ)
 		if err != nil {
 			return "", err
diff --git a/internal/backend/llvm/lower_test.go b/internal/backend/llvm/lower_test.go
index 15238097..99ab19f6 100644
--- a/internal/backend/llvm/lower_test.go
+++ b/internal/backend/llvm/lower_test.go
@@ -1362,6 +1362,30 @@ fn main(items: []i32) -> usize {
 	}
 }
 
+func TestLowerProgramFunctionArrayParamUsesByValAggregate(t *testing.T) {
+	root := t.TempDir()
+	mustWrite(t, filepath.Join(root, "main.fer"), `
+fn add(values: [2]i32) -> i32 {
+    return values[0] + values[1]
+}
+
+fn main() -> i32 {
+    return add([2]i32{1, 2})
+}
+`)
+	result := compiler.ParsePath(filepath.Join(root, "main.fer"))
+	if result.Diagnostics.HasErrors() {
+		t.Fatalf("unexpected diagnostics: %#v", result.Diagnostics.Diagnostics())
+	}
+	text, err := llvmbackend.LowerProgram(testUnits(result), false)
+	if err != nil {
+		t.Fatalf("lower llvm: %v", err)
+	}
+	if !strings.Contains(text, "define i32 @main__add(ptr byval([8 x i8]) align 4 %values)") {
+		t.Fatalf("expected array parameter lowered as byval aggregate:\n%s", text)
+	}
+}
+
 func TestLowerBuiltinLenStringToLLVM(t *testing.T) {
 	root := t.TempDir()
 	mustWrite(t, filepath.Join(root, "main.fer"), `