Lift variable accesses in continue blocks out to loop header.

spirv_cross.cpp

@@ -1976,6 +1976,8 @@ void Compiler::parse(const Instruction &instruction)
 		loop_blocks.insert(current_block->self);
 		loop_merge_targets.insert(current_block->merge_block);
 
+		continue_block_to_loop_header[current_block->continue_block] = current_block->self;
+
 		// Don't add loop headers to continue blocks,
 		// which would make it impossible branch into the loop header since
 		// they are treated as continues.
@@ -3214,6 +3216,10 @@ void Compiler::analyze_variable_scope(SPIRFunction &entry)
 				auto *var = compiler.maybe_get<SPIRVariable>(ptr);
 				if (var && var->storage == StorageClassFunction)
 					accessed_variables_to_block[var->self].insert(current_block->self);
+
+				for (uint32_t i = 3; i < length; i++)
+					if (id_is_phi_variable(args[i]))
+						accessed_variables_to_block[args[i]].insert(current_block->self);
 				break;
 			}
 
@@ -3352,16 +3358,27 @@ void Compiler::analyze_variable_scope(SPIRFunction &entry)
 		{
 			// If we're accessing a variable inside a continue block, this variable might be a loop variable.
 			// We can only use loop variables with scalars, as we cannot track static expressions for vectors.
-			if (this->is_continue(block) && type.vecsize == 1 && type.columns == 1)
+			if (this->is_continue(block))
 			{
-				// The variable is used in multiple continue blocks, this is not a loop
-				// candidate, signal that by setting block to -1u.
-				auto &potential = potential_loop_variables[var.first];
+				// Potentially awkward case to check for.
+				// We might have a variable inside a loop, which is touched by the continue block,
+				// but is not actually a loop variable.
+				// The continue block is dominated by the inner part of the loop, which does not make sense in high-level
+				// language output because it will be declared before the body,
+				// so we will have to lift the dominator up to the relevant loop header instead.
+				builder.add_block(continue_block_to_loop_header[block]);
 
-				if (potential == 0)
-					potential = block;
-				else
-					potential = ~(0u);
+				if (type.vecsize == 1 && type.columns == 1)
+				{
+					// The variable is used in multiple continue blocks, this is not a loop
+					// candidate, signal that by setting block to -1u.
+					auto &potential = potential_loop_variables[var.first];
+
+					if (potential == 0)
+						potential = block;
+					else
+						potential = ~(0u);
+				}
 			}
 			builder.add_block(block);
 		}
@@ -3370,6 +3387,7 @@ void Compiler::analyze_variable_scope(SPIRFunction &entry)
 
 		// Add it to a per-block list of variables.
 		uint32_t dominating_block = builder.get_dominator();
+
 		// If all blocks here are dead code, this will be 0, so the variable in question
 		// will be completely eliminated.
 		if (dominating_block)

spirv_cross.hpp

@@ -511,6 +511,7 @@ protected:
 	std::unordered_set<uint32_t> loop_merge_targets;
 	std::unordered_set<uint32_t> selection_merge_targets;
 	std::unordered_set<uint32_t> multiselect_merge_targets;
+	std::unordered_map<uint32_t, uint32_t> continue_block_to_loop_header;
 
 	virtual std::string to_name(uint32_t id, bool allow_alias = true) const;
 	bool is_builtin_variable(const SPIRVariable &var) const;

spirv_glsl.cpp

@@ -7846,6 +7846,9 @@ bool CompilerGLSL::attempt_emit_loop_header(SPIRBlock &block, SPIRBlock::Method
 			{
 			case SPIRBlock::ForLoop:
 			{
+				// This block may be a dominating block, so make sure we flush undeclared variables before building the for loop header.
+				flush_undeclared_variables(block);
+
 				// Important that we do this in this order because
 				// emitting the continue block can invalidate the condition expression.
 				auto initializer = emit_for_loop_initializers(block);
@@ -7856,6 +7859,8 @@ bool CompilerGLSL::attempt_emit_loop_header(SPIRBlock &block, SPIRBlock::Method
 			}
 
 			case SPIRBlock::WhileLoop:
+				// This block may be a dominating block, so make sure we flush undeclared variables before building the while loop header.
+				flush_undeclared_variables(block);
 				statement("while (", to_expression(block.condition), ")");
 				break;