Added block.cases_32bit and reworked the cases fix

Now we added block.cases_32bit as requested and we only parse if the
remaining ops are a multiple of 2. None of them are mutable because we
return a reference of them depending of the op.condition width.

Signed-off-by: Sebastián Aedo <saedo@codeweavers.com>

spirv_cfg.cpp

@@ -135,8 +135,9 @@ bool CFG::post_order_visit(uint32_t block_id)
 		break;
 
 	case SPIRBlock::MultiSelect:
-		compiler.fix_switch_branches(block);
-		for (auto &target : block.cases)
+	{
+		const auto &cases = compiler.get_case_list(block);
+		for (const auto &target : cases)
 		{
 			if (post_order_visit(target.block))
 				add_branch(block_id, target.block);
@@ -144,6 +145,7 @@ bool CFG::post_order_visit(uint32_t block_id)
 		if (block.default_block && post_order_visit(block.default_block))
 			add_branch(block_id, block.default_block);
 		break;
+	}
 	default:
 		break;
 	}
@@ -385,7 +387,9 @@ void DominatorBuilder::lift_continue_block_dominator()
 		break;
 
 	case SPIRBlock::MultiSelect:
-		for (auto &target : block.cases)
+	{
+		auto &cases = cfg.get_compiler().get_case_list(block);
+		for (auto &target : cases)
 		{
 			if (cfg.get_visit_order(target.block) > post_order)
 				back_edge_dominator = true;
@@ -393,6 +397,7 @@ void DominatorBuilder::lift_continue_block_dominator()
 		if (block.default_block && cfg.get_visit_order(block.default_block) > post_order)
 			back_edge_dominator = true;
 		break;
+	}
 
 	default:
 		break;

spirv_common.hpp

@@ -857,7 +857,7 @@ struct SPIRBlock : IVariant
 		uint64_t value;
 		BlockID block;
 	};
-	mutable SmallVector<Case> cases;
+	SmallVector<Case> cases_32bit;
 	SmallVector<Case> cases_64bit;
 
 	// If we have tried to optimize code for this block but failed,

spirv_cross.cpp

@@ -1626,7 +1626,7 @@ SPIRBlock::ContinueBlockType Compiler::continue_block_type(const SPIRBlock &bloc
 	}
 }
 
-void Compiler::fix_switch_branches(const SPIRBlock &block) const
+const SmallVector<SPIRBlock::Case> &Compiler::get_case_list(const SPIRBlock &block) const
 {
 	auto search = ir.load_type_width.find(block.condition);
 	if (search == ir.load_type_width.end())
@@ -1636,7 +1636,9 @@ void Compiler::fix_switch_branches(const SPIRBlock &block) const
 
 	const uint32_t width = search->second;
 	if (width > 32)
-		block.cases = std::move(block.cases_64bit);
+		return block.cases_64bit;
+
+	return block.cases_32bit;
 }
 
 bool Compiler::traverse_all_reachable_opcodes(const SPIRBlock &block, OpcodeHandler &handler) const
@@ -3025,12 +3027,15 @@ void Compiler::AnalyzeVariableScopeAccessHandler::set_current_block(const SPIRBl
 		break;
 
 	case SPIRBlock::MultiSelect:
+	{
 		notify_variable_access(block.condition, block.self);
-		for (auto &target : block.cases)
+		auto &cases = compiler.get_case_list(block);
+		for (auto &target : cases)
 			test_phi(target.block);
 		if (block.default_block)
 			test_phi(block.default_block);
 		break;
+	}
 
 	default:
 		break;

spirv_cross.hpp

@@ -1117,7 +1117,11 @@ protected:
 	uint32_t evaluate_constant_u32(uint32_t id) const;
 
 	bool is_vertex_like_shader() const;
-	void fix_switch_branches(const SPIRBlock &block) const;
+
+	// Get the correct case list for the OpSwitch, since it can be either a
+	// 32 bit wide condition or a 64 bit, but the type is not embedded in the
+	// instruction itself.
+	const SmallVector<SPIRBlock::Case> &get_case_list(const SPIRBlock &block) const;
 
 private:
 	// Used only to implement the old deprecated get_entry_point() interface.

spirv_glsl.cpp

@@ -14789,7 +14789,8 @@ void CompilerGLSL::emit_block_chain(SPIRBlock &block)
 		// and let the default: block handle it.
 		// 2.11 in SPIR-V spec states that for fall-through cases, there is a very strict declaration order which we can take advantage of here.
 		// We only need to consider possible fallthrough if order[i] branches to order[i + 1].
-		for (auto &c : block.cases)
+		auto &cases = get_case_list(block);
+		for (auto &c : cases)
 		{
 			// It's safe to cast to uint32_t since we actually do a check
 			// previously that we're not using uint64_t as the switch selector.
@@ -14925,7 +14926,7 @@ void CompilerGLSL::emit_block_chain(SPIRBlock &block)
 		// If there is only one default block, and no cases, this is a case where SPIRV-opt decided to emulate
 		// non-structured exits with the help of a switch block.
 		// This is buggy on FXC, so just emit the logical equivalent of a do { } while(false), which is more idiomatic.
-		bool degenerate_switch = block.default_block != block.merge_block && block.cases.empty();
+		bool degenerate_switch = block.default_block != block.merge_block && block.cases_32bit.empty();
 
 		if (degenerate_switch || is_legacy_es())
 		{

spirv_parser.cpp

@@ -979,15 +979,20 @@ void Parser::parse(const Instruction &instruction)
 		current_block->default_block = ops[1];
 
 		uint32_t remaining_ops = length - 2;
-		for (uint32_t i = 2; i + 2 <= length; i += 2)
-			current_block->cases.push_back({ ops[i], ops[i + 1] });
+		if ((remaining_ops % 2) == 0)
+		{
+			for (uint32_t i = 2; i + 2 <= length; i += 2)
+				current_block->cases_32bit.push_back({ ops[i], ops[i + 1] });
+		}
 
 		if ((remaining_ops % 3) == 0)
+		{
 			for (uint32_t i = 2; i + 3 <= length; i += 3)
 			{
 				uint64_t value = (static_cast<uint64_t>(ops[i]) << 32) | ops[i + 1];
 				current_block->cases_64bit.push_back({ value, ops[i + 2] });
 			}
+		}
 
 		// If we jump to next block, make it break instead since we're inside a switch case block at that point.
 		ir.block_meta[current_block->next_block] |= ParsedIR::BLOCK_META_MULTISELECT_MERGE_BIT;
@@ -1145,7 +1150,7 @@ void Parser::parse(const Instruction &instruction)
 	// Actual opcodes.
 	default:
 	{
-		if (ops)
+		if (length >= 2)
 		{
 			const auto *type = maybe_get<SPIRType>(ops[0]);
 			if (type)