MSL: Re-roll array expressions in initializers.

We cannot rely on copy path when using an array as part of a struct
initializer, so reroll such expressions to an initializer list again.

reference/shaders-msl/comp/copy-array-of-arrays.comp

@@ -73,17 +73,11 @@ kernel void main0(device BUF& o [[buffer(0)]])
     o.a = int(c[1][1][1]);
     float _43[2] = { o.b, o.c };
     float _48[2] = { o.b, o.b };
-    float _49[2][2];
-    spvArrayCopyFromStack1(_49[0], _43);
-    spvArrayCopyFromStack1(_49[1], _48);
+    float _49[2][2] = { { _43[0], _43[1] }, { _48[0], _48[1] } };
     float _54[2] = { o.c, o.c };
     float _59[2] = { o.c, o.b };
-    float _60[2][2];
-    spvArrayCopyFromStack1(_60[0], _54);
-    spvArrayCopyFromStack1(_60[1], _59);
-    float _61[2][2][2];
-    spvArrayCopyFromStack2(_61[0], _49);
-    spvArrayCopyFromStack2(_61[1], _60);
+    float _60[2][2] = { { _54[0], _54[1] }, { _59[0], _59[1] } };
+    float _61[2][2][2] = { { { _49[0][0], _49[0][1] }, { _49[1][0], _49[1][1] } }, { { _60[0][0], _60[0][1] }, { _60[1][0], _60[1][1] } } };
     float d[2][2][2];
     spvArrayCopyFromStack3(d, _61);
     float e[2][2][2];

spirv_glsl.cpp

@@ -2886,6 +2886,49 @@ string CompilerGLSL::to_extract_component_expression(uint32_t id, uint32_t index
 		return join(expr, ".", index_to_swizzle(index));
 }
 
+string CompilerGLSL::to_rerolled_array_expression(const string &base_expr, const SPIRType &type)
+{
+	uint32_t size = to_array_size_literal(type);
+	auto &parent = get<SPIRType>(type.parent_type);
+	string expr = "{ ";
+
+	for (uint32_t i = 0; i < size; i++)
+	{
+		auto subexpr = join(base_expr, "[", convert_to_string(i), "]");
+		if (parent.array.empty())
+			expr += subexpr;
+		else
+			expr += to_rerolled_array_expression(subexpr, parent);
+
+		if (i + 1 < size)
+			expr += ", ";
+	}
+
+	expr += " }";
+	return expr;
+}
+
+string CompilerGLSL::to_composite_constructor_expression(uint32_t id)
+{
+	auto &type = expression_type(id);
+	if (!backend.array_is_value_type && !type.array.empty())
+	{
+		// For this case, we need to "re-roll" an array initializer from a temporary.
+		// We cannot simply pass the array directly, since it decays to a pointer and it cannot
+		// participate in a struct initializer. E.g.
+		// float arr[2] = { 1.0, 2.0 };
+		// Foo foo = { arr }; must be transformed to
+		// Foo foo = { { arr[0], arr[1] } };
+		// The array sizes cannot be deduced from specialization constants since we cannot use any loops.
+
+		// We're only triggering one read of the array expression, but this is fine since arrays have to be declared
+		// as temporaries anyways.
+		return to_rerolled_array_expression(to_enclosed_expression(id), type);
+	}
+	else
+		return to_expression(id);
+}
+
 string CompilerGLSL::to_expression(uint32_t id, bool register_expression_read)
 {
 	auto itr = invalid_expressions.find(id);
@@ -7302,7 +7345,7 @@ string CompilerGLSL::build_composite_combiner(uint32_t return_type, const uint32
 
 			if (i)
 				op += ", ";
-			subop = to_expression(elems[i]);
+			subop = to_composite_constructor_expression(elems[i]);
 		}
 
 		base = e ? e->base_expression : 0;
@@ -7858,15 +7901,7 @@ void CompilerGLSL::emit_instruction(const Instruction &instruction)
 			forward = false;
 
 		string constructor_op;
-		if (!backend.array_is_value_type && out_type.array.size() > 1)
-		{
-			// We cannot construct array of arrays because we cannot treat the inputs
-			// as value types. Need to declare the array-of-arrays, and copy in elements one by one.
-			emit_uninitialized_temporary_expression(result_type, id);
-			for (uint32_t i = 0; i < length; i++)
-				emit_array_copy(join(to_expression(id), "[", i, "]"), elems[i]);
-		}
-		else if (backend.use_initializer_list && composite)
+		if (backend.use_initializer_list && composite)
 		{
 			// Only use this path if we are building composites.
 			// This path cannot be used for arithmetic.

spirv_glsl.hpp

@@ -502,6 +502,8 @@ protected:
 	SPIRExpression &emit_uninitialized_temporary_expression(uint32_t type, uint32_t id);
 	void append_global_func_args(const SPIRFunction &func, uint32_t index, SmallVector<std::string> &arglist);
 	std::string to_expression(uint32_t id, bool register_expression_read = true);
+	std::string to_composite_constructor_expression(uint32_t id);
+	std::string to_rerolled_array_expression(const std::string &expr, const SPIRType &type);
 	std::string to_enclosed_expression(uint32_t id, bool register_expression_read = true);
 	std::string to_unpacked_expression(uint32_t id, bool register_expression_read = true);
 	std::string to_enclosed_unpacked_expression(uint32_t id, bool register_expression_read = true);

spirv_msl.cpp

@@ -8691,14 +8691,6 @@ CompilerMSL::SPVFuncImpl CompilerMSL::OpCodePreprocessor::get_spv_func_impl(Op o
 			return SPVFuncImplTextureSwizzle;
 		break;
 
-	case OpCompositeConstruct:
-	{
-		auto &type = compiler.get<SPIRType>(args[0]);
-		if (type.array.size() > 1) // We need to use copies to build the composite.
-			return static_cast<SPVFuncImpl>(SPVFuncImplArrayCopyMultidimBase + type.array.size() - 1);
-		break;
-	}
-
 	case OpExtInst:
 	{
 		uint32_t extension_set = args[2];