From eaf42fab015441ac286a6eb4e8e1853866091221 Mon Sep 17 00:00:00 2001
From: "Darryl L. Miles" <darryl.miles@darrylmiles.org>
Date: Thu, 23 Jul 2026 14:49:37 +0000
Subject: [PATCH] build: remove the depend phase/barrier from the top Makefile

With per-file dependencies now generated during compilation (previous commit),
the serial `depend` phase and its barrier are obsolete.  Drop SUBDIRS_DEPEND and
the `<dir>/Depend: ${DATABASE_H}` rule, and replace the `module@/lib@/tech@ %:
depend` prerequisite with `: ${DATABASE_H}` -- the only real ordering constraint
is the generated header, not a whole dependency-scanning pass.  Modules therefore
start compiling in parallel immediately instead of waiting for every subdir's
deps to be scanned first.

`make depend` is kept as a top-level no-op (the WASM build script still calls
`emmake make depend`).

Verified out-of-tree serial and -j12 and in-tree -j12: rc=0, 375 files, serial
and -j installs byte-identical, zero Depend files, source tree clean.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
---
 Makefile.in | 28 +++++++++++++---------------
 1 file changed, 13 insertions(+), 15 deletions(-)

diff --git a/Makefile.in b/Makefile.in
index 34c9a389..90663178 100644
--- a/Makefile.in
+++ b/Makefile.in
@@ -96,15 +96,16 @@ ${DATABASE_H}: ${MAGICSRC}/database/database.h.in
 prepare: ${DATABASE_H}
 
 # module@<dir> builds <dir>/lib<dir>.o; lib@<dir> builds <dir>/lib<dir>.a.
-# Every module@/lib@ waits for the whole `depend` phase first (it used to be a
-# prereq of the `modules`/`libs` aggregates; moving it onto each per-dir target
-# keeps depend before compilation even under -j).
+# The only thing they must wait for is the generated header (${DATABASE_H}).
+# Header *dependencies* are now discovered automatically per source (.deps, see
+# rules.mak), so there is no separate `depend` phase to gate on -- modules start
+# compiling in parallel immediately.
 MODULE_TARGETS := $(addprefix module@,${MODULES})
 LIB_TARGETS    := $(addprefix lib@,${MODULES})
 .PHONY: $(MODULE_TARGETS) $(LIB_TARGETS)
-$(MODULE_TARGETS): module@%: depend
+$(MODULE_TARGETS): module@%: ${DATABASE_H}
 	@$(call submake,$*,module)
-$(LIB_TARGETS): lib@%: depend
+$(LIB_TARGETS): lib@%: ${DATABASE_H}
 	@$(call submake,$*,lib)
 
 # Cross-module archive edge (-j correctness): libdatabase.a physically archives
@@ -129,23 +130,20 @@ SUBDIRS = bplane cmwind commands database dbwind debug drc extflat extract graph
 
 BUNDLED_MODULES = readline lisp
 
-# Unique list of all subdir that might have Depend file, we have to deduplicate otherwise
-# MAKE will warning loudly.  This list is somewhat empty when defs.mak does not exist
+# Unique, deduplicated subdir list (used by the clean fan-out below).
 SUBDIRS_FILTERED := $(shell echo ${MODULES} ${PROGRAMS} ${SUBDIRS} | tr ' ' '\n' | sort | uniq)
 
-SUBDIRS_DEPEND = $(addsuffix /Depend, ${SUBDIRS_FILTERED})
-
-${SUBDIRS_DEPEND}: ${DATABASE_H}
-	@echo --- making dependencies
-	@$(call submake,$(patsubst %/,%,$(dir $@)),depend)
-
+# Dependencies are generated automatically as a side effect of compiling (see
+# rules.mak .deps); there is no depend phase to run.  "make depend" is kept as a
+# no-op so callers that still invoke it (e.g. the WASM build script) do not error.
 .PHONY: depend
-depend: defs.mak ${SUBDIRS_DEPEND}
+depend:
+	@echo "--- dependencies are generated automatically during compilation"
 
 # tech@<dir>: build a technology dir (goal "all").
 TECH_TARGETS := $(addprefix tech@,${TECHS})
 .PHONY: $(TECH_TARGETS)
-$(TECH_TARGETS): tech@%: depend
+$(TECH_TARGETS): tech@%: ${DATABASE_H}
 	@$(call submake,$*,all)
 
 .PHONY: techs