Work on #14, can now return small (<= 4 bytes) structs from functions

src/regalloc.cpp

@@ -22,6 +22,11 @@ static bool CanTypeFitInNativeRegister(const Type* type)
 		return true;
 	}
 
+	if (type->IsStruct()) {
+		const size_t structSize = ARMv7::TypeSize(type);
+		return structSize <= 4;
+	}
+
 	return false;
 }
 
@@ -77,6 +82,10 @@ static const Type* LowerVirtualRegisterType(const Type* type) {
 	}
 	else if (type->IsIntegral()) {
 		return type;
+	} else if (type->IsStruct()) {
+		if (ARMv7::TypeSize(type) <= 4) {
+			return BuiltinTypes::GetInt32();
+		}
 	}
 
 	helix_unreachable("type cannot be lowered into a single physical register");
@@ -303,7 +312,7 @@ void RegisterAllocator::Execute(Function* fn)
 		//where = head->InsertAfter(where, Helix::CreateIntToPtr(BuiltinTypes::GetInt32(), temp, output_ptr));
 //
 //
-		Instruction* lastInsn = output_ptr->GetUse(0).GetInstruction();
+		//Instruction* lastInsn = output_ptr->GetUse(0).GetInstruction();
 		int c = 0;
 
 		struct T { Use use; PhysicalRegisterName* reg; };

testsuite/f5/f5013-cconv-return-small-struct.c

@@ -0,0 +1,10 @@
+struct MyStruct
+{
+  int a;
+};
+
+struct MyStruct get_small_struct()
+{
+  struct MyStruct a = { 33 };
+  return a;
+}

testsuite/f5/f5013-cconv-return-small-struct.xml

@@ -0,0 +1,32 @@
+<Test>
+	<Flags>--emit-ir-post=cconv -c</Flags>
+
+	<TestFlags>
+		<TestFlag name="regex" value="false"></TestFlag>
+	</TestFlags>
+
+	<ExpectedOutput>
+MyStruct = struct { i32 }
+
+@ci0:ptr = global i32 0:i32
+@ci1:ptr = global i32 33:i32
+
+function get_small_struct(): void {
+.0:
+	stack_alloc [MyStruct x 1], %0:ptr
+	stack_alloc [MyStruct x 1], %1:ptr
+	ptrtoint [ptr -> i32], %1:ptr, %2:i32
+	load @ci0:ptr, %3:i32
+	iadd %2:i32, %3:i32, %4:i32
+	inttoptr [i32 -> ptr], %4:i32, %5:ptr
+	load @ci1:ptr, %6:i32
+	store %6:i32, %5:ptr
+	load %1:ptr, %7:MyStruct
+	store %7:MyStruct, %0:ptr
+	br .1
+.1:
+	load %0:ptr, r0:i32
+	ret
+}
+	</ExpectedOutput>
+</Test>