diff --git a/scripts/duffle.lua b/scripts/duffle.lua
index 78d4ada..80470ac 100644
--- a/scripts/duffle.lua
+++ b/scripts/duffle.lua
@@ -2236,6 +2236,36 @@ local function _project_emission_inner(root_body_entry, ctx_table)
 	local invocation_stack = {}   -- stack of currently-open invocation records
 	local next_inv_id      = 0
 
+	local reg_use_schema = ctx_table.reg_use_schema
+	local reg_use_param  = ctx_table.reg_use_param
+	local atom_name      = ctx_table.atom_name
+
+	local slot_readonly = {}
+	if reg_use_schema then
+		for _, slot in ipairs(reg_use_schema.slots or {}) do
+			slot_readonly[slot.name] = slot.readonly == true
+		end
+	end
+
+	local function apply_sub(sub_map, operand)
+		if sub_map and type(operand) == "string" and sub_map[operand] then
+			return sub_map[operand]
+		end
+		return operand
+	end
+
+	local function resolve_gpr_key(operand)
+		if type(operand) ~= "string" then return nil end
+		if operand:sub(1, 2) == "R_" then return operand end
+		if not (reg_use_schema and reg_use_param) then return nil end
+		local prefix = reg_use_param .. "."
+		if operand:sub(1, #prefix) ~= prefix then return nil end
+		local member_path = operand:sub(#prefix + 1)
+		local slot = reg_use_schema.alias_to_slot[member_path]
+		if not slot then return nil, member_path end
+		return "reguse:" .. atom_name .. ":" .. slot, nil, slot
+	end
+
 	local function open_invocation_ids_snapshot()
 		local ids = {}
 		for _, inv in ipairs(invocation_stack) do
@@ -2246,7 +2276,7 @@ local function _project_emission_inner(root_body_entry, ctx_table)
 
 	local function emit_word(encoder, args, line, word_call_text,
 		def_source_now, def_line_now,
-		immediate_call_text, root_call_text_w)
+		immediate_call_text, root_call_text_w, sub_map)
 		local inv_ids   = open_invocation_ids_snapshot()
 		local outermost = inv_ids[1] or 0
 		-- For words emitted at the root atom body, `immediate_call_text` is nil and the walker's `word_call_text` (the word's own token, e.g. "nop") becomes the effective call_text.
@@ -2254,6 +2284,42 @@ local function _project_emission_inner(root_body_entry, ctx_table)
 		-- The call that triggered the body expansion we're currently walking.
 		local eff_call_text      = immediate_call_text or word_call_text
 		local eff_root_call_text = root_call_text_w
+		local gpr_keys = nil
+		if reg_use_schema or sub_map then
+			gpr_keys = {}
+			for pos, arg in ipairs(args or {}) do
+				local effective = apply_sub(sub_map, arg)
+				local key, unresolved, slot = resolve_gpr_key(effective)
+				gpr_keys[pos] = key
+				if unresolved then
+					errors[#errors + 1] = {
+						kind = "reguse_unresolved",
+						line = line,
+						msg  = string.format("RegUse operand %q does not resolve in schema %q",
+							effective, (reg_use_schema and reg_use_schema.name) or "?"),
+					}
+				end
+				if key and slot and slot_readonly[slot] then
+					local effects = M.INSTRUCTION_GPR_EFFECTS or {}
+					local row = effects[encoder]
+					if row and row.writes then
+						for _, wpos in ipairs(row.writes) do
+							if wpos == pos then
+								errors[#errors + 1] = {
+									kind = "reguse_const_write",
+									line = line,
+									msg  = string.format("RegUse slot %q is Reg const; %s writes it",
+										slot, encoder),
+								}
+							end
+						end
+					end
+				end
+			end
+		end
+		if not reg_use_schema then
+			gpr_keys = nil
+		end
 		items[#items + 1] = {
 			kind                     = "word",
 			encoder                  = encoder,
@@ -2265,6 +2331,7 @@ local function _project_emission_inner(root_body_entry, ctx_table)
 			root_call_text           = eff_root_call_text,
 			invocation_ids           = inv_ids,
 			outermost_invocation_id  = outermost,
+			gpr_keys                 = gpr_keys,
 		}
 		word_events[#word_events + 1] = {
 			i                        = word_idx,
@@ -2277,6 +2344,7 @@ local function _project_emission_inner(root_body_entry, ctx_table)
 			invocation_ids           = inv_ids,
 			outermost_invocation_id  = outermost,
 			word_count               = 1,
+			gpr_keys                 = gpr_keys,
 		}
 		word_idx = word_idx + 1
 	end
@@ -2520,6 +2588,7 @@ local function _project_emission_inner(root_body_entry, ctx_table)
 		local line_of    = body_entry.line_of or M.LineIndex("")
 		local def_source = body_entry.source or ""
 		local def_line   = body_entry.declaration or 0
+		local sub_map    = body_entry.sub_map
 		-- Per-token dispatch: each matched branch returns; only the fall-through
 		-- "opaque word" emit handles direct encoders + mac_X-without-component.
 		local function process_token(bt)
@@ -2575,12 +2644,22 @@ local function _project_emission_inner(root_body_entry, ctx_table)
 					-- Propagate trackers into the recursive walk:
 					--   immediate_call_text = this call's tok (the IMMEDIATE outer call for words emitted in this body)
 					--   root_call_text      = the OUTERMOST call (immutable across the recursion)
+					local formal_names = ctx_table.component_index[bare]
+						and ctx_table.component_index[bare].arg_names
+					local child_map = nil
+					if formal_names then
+						child_map = {}
+						for i, fname in ipairs(formal_names) do
+							child_map[fname] = apply_sub(sub_map, args[i])
+						end
+					end
 					walk_body_entry({
 							body_tokens = comp.body_tokens or {},
 							body_off    = comp.body_off or 0,
 							line_of     = comp.line_of,
 							source      = comp.source,
 							declaration = comp.declaration,
+							sub_map     = child_map,
 						},
 						inv.id,
 						invocation_root_call_text,
@@ -2618,7 +2697,7 @@ local function _project_emission_inner(root_body_entry, ctx_table)
 			local n         = resolve_count(ident, tok_line)
 			local out_ident = (ident == "nop2") and "nop" or ident
 			for _ = 1, n do
-				emit_word(out_ident, args, tok_line, tok, def_source, def_line, walk_immediate_call_text, walk_root_call_text)
+				emit_word(out_ident, args, tok_line, tok, def_source, def_line, walk_immediate_call_text, walk_root_call_text, sub_map)
 			end
 		end
 		
@@ -2683,7 +2762,7 @@ end
 --- @param components      table   -- bare-name → component definition (corpus.components); REQUIRED — consumed at the invocation-construction site to stamp
 ---                                   `invocation.debug_skip`. A missing or non-table `components` raises a fail-loud error rather than silently falling back.
 --- @return EmissionProjection
-function M.project_emission(body_text, component_index, word_counts, components)
+function M.project_emission(body_text, component_index, word_counts, components, reg_use_ctx)
 	-- The recursive walk delegates to `_project_emission_inner` so component bodies (which arrive as
 	-- `{body_tokens, body_off, line_of, source, declaration}` records from `corpus.component_body_index`)
 	-- re-enter the same walker with the same shared output state.
@@ -2726,6 +2805,10 @@ function M.project_emission(body_text, component_index, word_counts, components)
 		component_index = component_index or {},
 		word_counts     = word_counts     or {},
 		components      = components,
+		reg_use_schema  = reg_use_ctx and reg_use_ctx.reg_use_schema,
+		reg_use_param   = reg_use_ctx and reg_use_ctx.reg_use_param,
+		atom_name       = reg_use_ctx and reg_use_ctx.atom_name,
+		schema_name     = reg_use_ctx and reg_use_ctx.schema_name,
 	})
 end
 
@@ -2860,13 +2943,12 @@ function M.find_atom_proc_decl_for(source, before_pos, mips_atom_ptr_len)
 		if source:sub(next_pos, next_pos) == "(" then
 			local inner = M.read_parens(source, next_pos)
 			if inner then
-				-- strip the _proc suffix to get the atom name
 				local proc_suffix = "_proc"
+				local atom_name = ident
 				if #ident > #proc_suffix and ident:sub(-#proc_suffix) == proc_suffix then
-					return ident:sub(1, #ident - #proc_suffix), inner
+					atom_name = ident:sub(1, #ident - #proc_suffix)
 				end
-				-- no _proc suffix — return as-is
-				return ident, inner
+				return atom_name, inner, ident
 			end
 		end
 		-- ident not followed by "(" — it's a qualifier; skip it
diff --git a/scripts/passes/components.lua b/scripts/passes/components.lua
index 369feb6..c11519a 100644
--- a/scripts/passes/components.lua
+++ b/scripts/passes/components.lua
@@ -159,6 +159,14 @@ local function extract_arg_names(args_str)
 	return names
 end
 
+local function formal_arg_names(args_str)
+	local names = extract_arg_names(args_str)
+	if not names then return nil end
+	if names[1] == "ab" then table.remove(names, 1) end
+	if #names == 0 then return nil end
+	return names
+end
+
 -- ════════════════════════════════════════════════════════════════════════════
 -- Component projection (read from pre-scanned SourceScan)
 -- ════════════════════════════════════════════════════════════════════════════
@@ -197,6 +205,7 @@ local function project_components(source, scan)
 				body_off    = a.body_off,
 				body_tokens = a.body_tokens,
 				args        = args,
+				arg_names   = formal_arg_names(args),
 				comment     = comment,
 				kind        = a.kind,  -- "comp_bare" | "comp_proc"; provenance emitter reads this.
 				debug_skip  = a.debug_skip == true,
@@ -466,18 +475,9 @@ end
 --- @param args_str string|nil
 --- @return string
 local function signature_from_args(args_str)
-	local arg_names = extract_arg_names(args_str)
-	if    arg_names and #arg_names > 0 then
-		-- Drop the leading `ab` (atom-builder) first arg if present.
-		-- Convention: `MipsAtomComp_Proc_` components always declare `ab` as the first function-arg
-		-- (type `MipsAtomBuilder_R`), mirroring the macro signature in `lottes_tape.h`.
-		if arg_names[1] == "ab" then
-			table.remove(arg_names, 1)
-		end
-		if #arg_names > 0 then
-			return table.concat(arg_names, ", ")
-		end
-		return "..."  -- `ab` was the only arg; fall through to variadic
+	local names = formal_arg_names(args_str)
+	if names then
+		return table.concat(names, ", ")
 	end
 	return "..."
 end
@@ -710,6 +710,7 @@ local function update_canonical_component_body_index(corpus, src, components, sc
 				source      = src.path,
 				declaration = c.line,
 				kind        = c.kind,
+				arg_names   = c.arg_names,
 			}
 		end
 	end
diff --git a/scripts/passes/emission_model.lua b/scripts/passes/emission_model.lua
index 7d60291..c3a0248 100644
--- a/scripts/passes/emission_model.lua
+++ b/scripts/passes/emission_model.lua
@@ -155,8 +155,28 @@ local function project_atom(atom_record, src, corpus)
 	local body  = atom_record.body or ""
 	local wc    = corpus.word_counts or {}
 	local cbi   = corpus.component_body_index or {}
+	local schema = nil
+	if atom_record.reg_use_schema_name then
+		schema = corpus.reg_use_schemas and corpus.reg_use_schemas[atom_record.reg_use_schema_name]
+	end
 	-- That construction site stamps `invocation.debug_skip` while appending each record to `proj.invocations`.
-	local proj  = duffle.project_emission(body, cbi, wc, corpus.components)
+	local proj  = duffle.project_emission(body, cbi, wc, corpus.components, {
+		reg_use_schema = schema,
+		reg_use_param  = atom_record.reg_use_param_name,
+		atom_name      = atom_record.name,
+		schema_name    = atom_record.reg_use_schema_name,
+	})
+	if atom_record.reg_use_schema_name and not schema then
+		proj.errors[#proj.errors + 1] = {
+			kind = "reguse_missing_schema",
+			msg  = string.format("RegUse schema %q is missing", atom_record.reg_use_schema_name),
+		}
+	end
+	for _, err in ipairs(corpus.reg_use_errors or {}) do
+		if err.schema_name == atom_record.reg_use_schema_name then
+			proj.errors[#proj.errors + 1] = err
+		end
+	end
 	local paths = {
 		tokens       = atom_record.body_tokens or {},
 		line_in_body = duffle.build_body_line_index(body),
diff --git a/scripts/passes/scan_source.lua b/scripts/passes/scan_source.lua
index b034ed5..29c986a 100644
--- a/scripts/passes/scan_source.lua
+++ b/scripts/passes/scan_source.lua
@@ -1416,13 +1416,49 @@ local function parse_mips_atom_proc(source, pos, ident_end, line_of, out)
 	-- (`internal MipsAtom* X_proc(...)`), not from the first macro arg (which
 	-- is now `aa`). The backward walk finds the function decl before open_paren
 	-- and strips the `_proc` suffix.
-	local raw_name = duffle.find_atom_proc_decl_for(source, open_paren, MIPS_ATOM_PTR_LEN)
+	local raw_name, args_inner, func_ident = duffle.find_atom_proc_decl_for(source, open_paren, MIPS_ATOM_PTR_LEN)
 	if not raw_name then raw_name = "?" end
-	local name     = strip_ac_prefix(raw_name)
+	local name = strip_ac_prefix(raw_name)
+	local reg_use_schema_name = nil
+	local reg_use_param_name  = nil
+	if args_inner then
+		local arg_tokens = duffle.split_top_level_commas(args_inner)
+		for _, tok in ipairs(arg_tokens) do
+			local trimmed = duffle.trim(tok)
+			local schema_suffix, param = trimmed:match("RegUse_([%w_]+)%s+([%w_]+)$")
+			if schema_suffix then
+				if reg_use_schema_name then
+					out.reg_use_errors[#out.reg_use_errors + 1] = {
+						kind        = "reguse_multiple_params",
+						schema_name = "RegUse_" .. schema_suffix,
+						source_line = line_of(pos),
+					}
+				else
+					reg_use_schema_name = "RegUse_" .. schema_suffix
+					reg_use_param_name  = param
+				end
+			end
+		end
+	end
 	-- Position of body[1] in source = open_paren + 1 (start of inner) + last_brace_pos + 1 (past '{').
 	local body_off = open_paren + 2 + last_brace_pos
 	register_atom(out, "atom_proc", line_of(pos), name, body, body_off, raw_name, pos, after_paren, source)
 
+	local entry = out.atoms[#out.atoms]
+	entry.reg_use_schema_name = reg_use_schema_name
+	entry.reg_use_param_name  = reg_use_param_name
+	if reg_use_schema_name and func_ident then
+		local expected = "RegUse_" .. func_ident
+		if reg_use_schema_name ~= expected then
+			out.reg_use_errors[#out.reg_use_errors + 1] = {
+				kind        = "reguse_name_mismatch",
+				schema_name = reg_use_schema_name,
+				func_ident  = func_ident,
+				source_line = line_of(pos),
+			}
+		end
+	end
+
 	return after_paren
 end
 
@@ -1530,6 +1566,171 @@ local function register_typedef_alias(underlying, name, pos, line_of, out)
 	}
 end
 
+local function parse_reg_use_schema_body(body)
+	local slots = {}
+	local alias_to_slot = {}
+	local slot_names = {}
+	local errors = {}
+
+	local function add_alias(path, slot)
+		if alias_to_slot[path] then
+			errors[#errors + 1] = { kind = "reguse_duplicate_alias", path = path }
+			return false
+		end
+		alias_to_slot[path] = slot
+		return true
+	end
+
+	local function add_slot(name, aliases, readonly)
+		if slot_names[name] then
+			errors[#errors + 1] = { kind = "reguse_duplicate_slot", name = name }
+			return nil
+		end
+		slot_names[name] = true
+		local slot = { name = name, aliases = aliases, readonly = readonly == true }
+		slots[#slots + 1] = slot
+		return slot
+	end
+
+	local function parse_reg_names(text, pos)
+		local names = {}
+		while pos <= #text do
+			pos = duffle.skip_ws_and_cmt(text, pos)
+			local name, name_end = duffle.read_ident(text, pos)
+			if not name then return nil, pos end
+			names[#names + 1] = name
+			pos = duffle.skip_ws_and_cmt(text, name_end)
+			if text:sub(pos, pos) == "," then
+				pos = pos + 1
+			else
+				break
+			end
+		end
+		if text:sub(pos, pos) == ";" then pos = pos + 1 end
+		return names, pos
+	end
+
+	local pos = 1
+	while pos <= #body do
+		pos = duffle.skip_ws_and_cmt(body, pos)
+		if pos > #body then break end
+		local first, first_end = duffle.read_ident(body, pos)
+		if not first then
+			pos = pos + 1
+			goto continue
+		end
+		local after = duffle.skip_ws_and_cmt(body, first_end)
+		if first == "const" then
+			errors[#errors + 1] = { kind = "reguse_const_reg_spelling" }
+			return nil, errors
+		elseif first == "union" then
+			if body:sub(after, after) ~= "{" then
+				errors[#errors + 1] = { kind = "reguse_malformed" }
+				return nil, errors
+			end
+			local inner, after_braces = duffle.read_braces(body, after)
+			if not inner then
+				errors[#errors + 1] = { kind = "reguse_malformed" }
+				return nil, errors
+			end
+			local members = {}
+			local union_readonly = nil
+			local inner_pos = 1
+			while inner_pos <= #inner do
+				inner_pos = duffle.skip_ws_and_cmt(inner, inner_pos)
+				if inner_pos > #inner then break end
+				local m_type, m_type_end = duffle.read_ident(inner, inner_pos)
+				if not m_type then
+					inner_pos = inner_pos + 1
+					goto continue_inner
+				end
+				if m_type == "const" then
+					errors[#errors + 1] = { kind = "reguse_const_reg_spelling" }
+					return nil, errors
+				end
+				if m_type ~= "Reg" then
+					errors[#errors + 1] = { kind = "reguse_malformed" }
+					return nil, errors
+				end
+				local m_after = duffle.skip_ws_and_cmt(inner, m_type_end)
+				local m_readonly = false
+				local maybe_const, maybe_end = duffle.read_ident(inner, m_after)
+				if maybe_const == "const" then
+					m_readonly = true
+					m_after = duffle.skip_ws_and_cmt(inner, maybe_end)
+				end
+				if union_readonly == nil then
+					union_readonly = m_readonly
+				elseif union_readonly ~= m_readonly then
+					errors[#errors + 1] = { kind = "reguse_mixed_const" }
+					return nil, errors
+				end
+				local names, new_inner = parse_reg_names(inner, m_after)
+				if not names or #names == 0 then
+					errors[#errors + 1] = { kind = "reguse_malformed" }
+					return nil, errors
+				end
+				for _, n in ipairs(names) do members[#members + 1] = n end
+				inner_pos = new_inner
+				::continue_inner::
+			end
+			if #members == 0 then
+				errors[#errors + 1] = { kind = "reguse_malformed" }
+				return nil, errors
+			end
+			local after_close = duffle.skip_ws_and_cmt(body, after_braces)
+			local inst_name, inst_end = duffle.read_ident(body, after_close)
+			local aliases = {}
+			local slot_name
+			if inst_name then
+				slot_name = inst_name
+				for _, m in ipairs(members) do
+					local path = inst_name .. "." .. m
+					if not add_alias(path, slot_name) then return nil, errors end
+					aliases[#aliases + 1] = path
+				end
+				after_close = inst_end
+			else
+				slot_name = members[1]
+				for _, m in ipairs(members) do
+					if not add_alias(m, slot_name) then return nil, errors end
+					aliases[#aliases + 1] = m
+				end
+			end
+			if not add_slot(slot_name, aliases, union_readonly) then return nil, errors end
+			after_close = duffle.skip_ws_and_cmt(body, after_close)
+			if body:sub(after_close, after_close) == ";" then after_close = after_close + 1 end
+			pos = after_close
+		elseif first == "Reg" then
+			local readonly = false
+			local maybe_const, maybe_end = duffle.read_ident(body, after)
+			if maybe_const == "const" then
+				readonly = true
+				after = duffle.skip_ws_and_cmt(body, maybe_end)
+			end
+			local names, new_pos = parse_reg_names(body, after)
+			if not names or #names == 0 then
+				errors[#errors + 1] = { kind = "reguse_malformed" }
+				return nil, errors
+			end
+			for _, n in ipairs(names) do
+				if not add_alias(n, n) then return nil, errors end
+				if not add_slot(n, { n }, readonly) then return nil, errors end
+			end
+			pos = new_pos
+		else
+			errors[#errors + 1] = { kind = "reguse_malformed" }
+			return nil, errors
+		end
+		::continue::
+	end
+	if #slots == 0 then
+		errors[#errors + 1] = { kind = "reguse_malformed" }
+		return nil, errors
+	end
+	return { slots = slots, alias_to_slot = alias_to_slot }, errors
+end
+
 --- Parse: `typedef` declarations.
 ---
 --- Recognizes four shapes:
@@ -1563,6 +1764,21 @@ local function parse_typedef_binds(source, pos, ident_end, line_of, out)
 		local body, after_brace = find_body_braces(source, after_paren, open_paren + 1)
 		if not body then return after_brace end
 		register_struct_type(body, name, pos, line_of, out)
+		if name:sub(1, 7) == "RegUse_" then
+			local schema, schema_errors = parse_reg_use_schema_body(body)
+			if schema then
+				schema.name        = name
+				schema.source_file = out._source_file
+				schema.source_line = line_of(pos)
+				out.reg_use_schemas[name] = schema
+			end
+			for _, err in ipairs(schema_errors or {}) do
+				err.schema_name = name
+				err.source_file = out._source_file
+				err.source_line = line_of(pos)
+				out.reg_use_errors[#out.reg_use_errors + 1] = err
+			end
+		end
 		attach_debug_skip_marker(out, "unrelated")
 		return after_brace
 
@@ -1954,6 +2170,8 @@ local function scan_source(source, source_file, code_macros, code_macro_bodies)
 		-- typedef chain walking (cycle-guarded, depth <= 8), and struct field sums.
 		-- See `propagate_type_sizes()` below.
 		type_name_registry = {},
+		reg_use_schemas    = {},
+		reg_use_errors     = {},
 		-- Shared `R_*_Code -> integer code` registry
 		-- (passed in from M.run pass 1; same reference so preprocessor intercept writes are visible to the enum-value resolver).
 		-- Stripped from `src.scan` before return.
@@ -2186,13 +2404,15 @@ local function merge_corpus_registries(corpus)
 	corpus.atom_auto_regs          = corpus.atom_auto_regs          or {}
 	corpus.phase_auto_regs         = corpus.phase_auto_regs         or {}
 	corpus.collisions              = corpus.collisions              or {}
+	corpus.reg_use_schemas         = corpus.reg_use_schemas         or {}
+	corpus.reg_use_errors          = corpus.reg_use_errors          or {}
 
 	-- Replace the existing corpus collections with empty tables so a re-run on the same corpus produces identical state (deterministic merge).
 	-- This is safe because M.run is the only writer to these tables within a single orchestrator invocation.
 	for _, key in ipairs({
 		"register_alias_registry", "type_name_registry", "binds_by_name",
 		"atoms_by_name", "atom_views", "atom_ctxs", "atom_phases",
-		"atom_infos", "collisions",
+		"atom_infos", "collisions", "reg_use_schemas", "reg_use_errors",
 	}) do
 		corpus[key] = {}
 	end
@@ -2285,6 +2505,15 @@ local function merge_corpus_registries(corpus)
 			for _, info in ipairs(scan.atom_infos or {}) do
 				corpus.atom_infos[#corpus.atom_infos + 1] = info
 			end
+
+			for name, schema in pairs(scan.reg_use_schemas or {}) do
+				if corpus.reg_use_schemas[name] == nil then
+					corpus.reg_use_schemas[name] = schema
+				end
+			end
+			for _, err in ipairs(scan.reg_use_errors or {}) do
+				corpus.reg_use_errors[#corpus.reg_use_errors + 1] = err
+			end
 		end
 	end
 end
diff --git a/scripts/passes/static_analysis.lua b/scripts/passes/static_analysis.lua
index 30c6bbd..a570c4e 100644
--- a/scripts/passes/static_analysis.lua
+++ b/scripts/passes/static_analysis.lua
@@ -451,6 +451,14 @@ local function is_cop2_consumer_of(consumer_event, destination, producer_rel)
 	return false
 end
 
+local function gpr_identity(event, pos)
+	local keys = event and event.gpr_keys
+	if keys and keys[pos] then return keys[pos] end
+	local arg = event and event.args and event.args[pos]
+	if type(arg) == "string" and arg:sub(1, 2) == "R_" then return arg end
+	return nil
+end
+
 -- True iff `consumer_event` reads the GPR operand at any position the destination register occupies.
 -- read_pos lookup consults `duffle.OPERAND_READ_POSITIONS` for the consumer's encoder and walks each `args[pos]` to find an operand-equal match.
 local function is_gpr_consumer_of(consumer_event, destination)
@@ -458,9 +466,8 @@ local function is_gpr_consumer_of(consumer_event, destination)
 	local read_pos       = duffle.OPERAND_READ_POSITIONS or {}
 	local positions      = read_pos[consumer_token]
 	if not positions then return false end
-	local args = consumer_event.args or {}
 	for _, pos in ipairs(positions) do
-		if args[pos] == destination then return true end
+		if gpr_identity(consumer_event, pos) == destination then return true end
 	end
 	return false
 end
@@ -552,6 +559,11 @@ local function is_gpr_operand(operand)
 	return type(operand) == "string" and operand:sub(1, 2) == "R_"
 end
 
+local function is_tracked_gpr(operand)
+	return is_gpr_operand(operand)
+		or (type(operand) == "string" and operand:sub(1, 7) == "reguse:")
+end
+
 local function constant_for_operand(gpr_values, operand)
 	if operand == "R_0" then return 0 end
 	local slot = is_gpr_operand(operand) and gpr_values[operand] or nil
@@ -560,13 +572,13 @@ local function constant_for_operand(gpr_values, operand)
 end
 
 local function invalidate_gpr(gpr_values, operand)
-	if is_gpr_operand(operand) and operand ~= "R_0" then
+	if is_tracked_gpr(operand) and operand ~= "R_0" then
 		gpr_values[operand] = { kind = "unknown" }
 	end
 end
 
 local function store_gpr_constant(gpr_values, operand, value)
-	if not is_gpr_operand(operand) or operand == "R_0" then return end
+	if not is_tracked_gpr(operand) or operand == "R_0" then return end
 	if value == nil then gpr_values[operand] = { kind = "unknown" }
 	else                 gpr_values[operand] = { kind = "constant", value = wrap_u4(value) }
 	end
@@ -629,26 +641,31 @@ end
 -- Encoders without an explicit effect row conservatively invalidate every R_-prefixed operand.
 -- Recognized value rules are evaluated before their destination is invalidated.
 -- A failed/unknown evaluation writes `{kind = "unknown"}` instead.
-local function apply_gpr_effects(ev_ident, ev_args, forward_state)
+local function apply_gpr_effects(ev, forward_state)
+	local ev_ident   = ev.encoder or ev.ident
+	local ev_args    = ev.args or {}
 	local gpr_values = forward_state.gpr_values
 	local effects    = duffle.INSTRUCTION_GPR_EFFECTS or {}
 	local row        = effects[ev_ident]
 	if row == nil then
-		for _, operand in ipairs(ev_args or {}) do
-			invalidate_gpr(gpr_values, operand)
+		for pos, operand in ipairs(ev_args) do
+			local key = gpr_identity(ev, pos) or operand
+			if type(key) == "string" and (key:sub(1, 2) == "R_" or key:sub(1, 7) == "reguse:") then
+				if key ~= "R_0" then gpr_values[key] = { kind = "unknown" } end
+			end
 		end
 		return
 	end
 
 	local value_rule = (duffle.GPR_VALUE_RULES or {})[ev_ident]
-	local value      = value_rule and evaluate_gpr_value_rule(value_rule, ev_args or {}, gpr_values) or nil
+	local value      = value_rule and evaluate_gpr_value_rule(value_rule, ev_args, gpr_values) or nil
 	for _, position in ipairs(row.writes or {}) do
-		local destination = ev_args and ev_args[position]
-		if is_gpr_operand(destination) then
+		local destination = gpr_identity(ev, position)
+		if destination then
 			if value_rule and position == value_rule.dest and value ~= nil then
 				store_gpr_constant(gpr_values, destination, value)
 			else
-				invalidate_gpr(gpr_values, destination)
+				if destination ~= "R_0" then gpr_values[destination] = { kind = "unknown" } end
 			end
 		end
 	end
@@ -953,7 +970,7 @@ local function analyze_hardware_relations(atom)
 		end
 
 		-- ── 2. Apply GPR value effects. ──
-		apply_gpr_effects(ev_ident, ev_args, forward)
+		apply_gpr_effects(ev, forward)
 
 		-- ── 3. Stage producers created by this event. ──
 		local rows = rows_by_token[ev_ident]
@@ -962,7 +979,7 @@ local function analyze_hardware_relations(atom)
 				-- `stage = false` rows document a direction but do not create a later command-input producer (SWC2 and ordinary MTC0).
 				if row.stage ~= false then
 					local dest_arg    = row.writes and row.writes.arg
-					local destination = dest_arg   and ev_args[dest_arg] or nil
+					local destination = dest_arg and (gpr_identity(ev, dest_arg) or ev_args[dest_arg]) or nil
 					if destination then
 						-- Apply the destination_match filter when present.
 						if row.destination_match and row.destination_match ~= destination then
@@ -1352,7 +1369,7 @@ local function check_hazard_nop_use(atom, _pipe_ctx, findings)
 			for _, row in ipairs(relations_table) do
 				if row.token == ev_ident and row.stage ~= false then
 					local dest_arg    = row.writes and row.writes.arg
-					local destination = dest_arg   and ev_args[dest_arg] or nil
+					local destination = dest_arg and (gpr_identity(ev, dest_arg) or ev_args[dest_arg]) or nil
 					if destination and (not row.destination_match or row.destination_match == destination) then
 						local required = row.visibility and row.visibility.required
 						if    required == nil and not (row.visibility and row.visibility.kind == "unknown_consumer") then
@@ -1517,11 +1534,12 @@ local function check_load_delay_slots(atom, pipe_ctx, findings)
 		-- Use `net_reads` to ignore RMW positions (write shadows read within the same instruction).
 		if not is_load then
 			for _, pos in ipairs(net_reads(event_ident, args)) do
-				local reg = args[pos]
-				if type(reg) == "string" and reg:sub(1, 2) == "R_" then
+				local reg = gpr_identity(event, pos)
+				if reg then
 					local until_idx = volatile_until[reg]
 					if until_idx and event_idx <= until_idx then
 						local ev_line = line_for_word_event(event)
+						local authored = args[pos] or reg
 						findings[#findings + 1] = {
 							atom  = atom.name,
 							line  = ev_line,
@@ -1530,7 +1548,7 @@ local function check_load_delay_slots(atom, pipe_ctx, findings)
 							msg   = string.format("%s at line %d reads %s at word %d, but a prior load's "
 								.. "delay slot is not over until word %d; insert a `nop` between the "
 								.. "load and this instruction.",
-								atom.name, ev_line, reg, event_idx, until_idx),
+								atom.name, ev_line, authored, event_idx, until_idx),
 						}
 					end
 				end
@@ -1541,8 +1559,8 @@ local function check_load_delay_slots(atom, pipe_ctx, findings)
 		local effect = gpr_effects[event_ident]
 		if effect and effect.writes then
 			for _, pos in ipairs(effect.writes) do
-				local reg = args[pos]
-				if type(reg) == "string" and reg:sub(1, 2) == "R_" then
+				local reg = gpr_identity(event, pos)
+				if reg then
 					if is_load then
 						-- Load: destination volatile for exactly 1 slot (the delay slot).
 						volatile_until[reg] = event_idx + 1