Track invariance dependencies separate from expression deps.

We need to be able to punch through any non-forwarded temporaries as
well.

Any SSA variable that is a dependency of an invariant store must be
flushed to temporary.

spirv_common.hpp

@@ -748,6 +748,10 @@ struct SPIRExpression : IVariant
 	// A list of expressions which this expression depends on.
 	SmallVector<ID> expression_dependencies;
 
+	// Similar as expression dependencies, but does not stop the tracking for force-temporary variables.
+	// We need to know the full chain from store back to any SSA variable.
+	SmallVector<ID> invariance_dependencies;
+
 	// By reading this expression, we implicitly read these expressions as well.
 	// Used by access chain Store and Load since we read multiple expressions in this case.
 	SmallVector<ID> implied_read_expressions;

spirv_cross.cpp

@@ -2569,6 +2569,11 @@ void Compiler::add_active_interface_variable(uint32_t var_id)
 
 void Compiler::inherit_expression_dependencies(uint32_t dst, uint32_t source_expression)
 {
+	auto *ptr_e = maybe_get<SPIRExpression>(dst);
+
+	if (is_position_invariant() && ptr_e && maybe_get<SPIRExpression>(source_expression))
+		ptr_e->invariance_dependencies.push_back(source_expression);
+
 	// Don't inherit any expression dependencies if the expression in dst
 	// is not a forwarded temporary.
 	if (forwarded_temporaries.find(dst) == end(forwarded_temporaries) ||
@@ -2577,7 +2582,7 @@ void Compiler::inherit_expression_dependencies(uint32_t dst, uint32_t source_exp
 		return;
 	}
 
-	auto &e = get<SPIRExpression>(dst);
+	auto &e = *ptr_e;
 	auto *phi = maybe_get<SPIRVariable>(source_expression);
 	if (phi && phi->phi_variable)
 	{

spirv_glsl.cpp

@@ -11772,7 +11772,7 @@ void CompilerGLSL::disallow_forwarding_in_expression_chain(const SPIRExpression
 		force_temporary_and_recompile(expr.self);
 		forced_invariant_temporaries.insert(expr.self);
 
-		for (auto &dependent : expr.expression_dependencies)
+		for (auto &dependent : expr.invariance_dependencies)
 			disallow_forwarding_in_expression_chain(get<SPIRExpression>(dependent));
 	}
 }