[PATCH 5/5] Run check-installed-headers concurrently for each header

[Adhemerval Zanella]

The check-installed-headers-c/-cxx tests ran one script invocation per
subdirectory over all of its installed headers, performing about 80
compiler invocations per header serially.

Give each header its own intermediate target so the compiler
invocations parallelize under the make jobserver, recording the
per-header script exit status next to the output.  The .out target
concatenates the per-header outputs in the original $(headers) order
and fails if any recorded status is non-zero, so both the .out contents
(verified byte-identical for all 76 files) and the tests.sum results
are unchanged.

Results on a x86_64 machine [1] from a make check with run-built-tests=no
show neutral results, and on aarch64 machine [2] it improves from 241.574s
to 182.405.

[1] Ryzen 5900x, 12c/24t, gcc 16.1.1, binutils 2.26, and GNU make 4.3
[2] N1, 80c, gcc 15.1.1, binutils 2.25, GNU make 4.3
---
 Makefile | 37 ++++++++++++++++++++++++++-----------
 Rules    | 38 +++++++++++++++++++++++++++-----------
 2 files changed, 53 insertions(+), 22 deletions(-)

diff --git a/Makefile b/Makefile
index 60b7c51437a..11d35e31b4f 100644
--- a/Makefile
+++ b/Makefile
@@ -655,26 +655,41 @@ $(objpfx)check-local-headers.out: scripts/check-local-headers.sh
 	$(evaluate-test)
 
 ifneq "$(headers)" ""
-# Special test of all the installed headers in this directory.
+# Special test of all the installed headers in this directory.  See
+# Rules for the per-header split rationale.
 tests-special += $(objpfx)check-installed-headers-c.out
 libof-check-installed-headers-c := testsuite
-$(objpfx)check-installed-headers-c.out: \
++cih-c-iouts := $(patsubst %,$(objpfx)check-installed-headers-c/%.iout,\
+			   $(headers))
+$(+cih-c-iouts): $(objpfx)check-installed-headers-c/%.iout: \
     scripts/check-installed-headers.sh $(headers)
-	$(SHELL) $(..)scripts/check-installed-headers.sh c $(supported-fortify) \
-	  "$(CC) $(test-config-cflags-finput-charset-ascii) \
-	     $(filter-out -std=%,$(CFLAGS)) -D_ISOMAC $(+includes)" \
-	  $(headers) > $@; \
+	$(make-target-directory)
+	($(SHELL) $(..)scripts/check-installed-headers.sh c $(supported-fortify) \
+	   "$(CC) $(test-config-cflags-finput-charset-ascii) \
+	      $(filter-out -std=%,$(CFLAGS)) -D_ISOMAC $(+includes)" \
+	   $*; echo $$? > $@-ret) > $@T; \
+	mv -f $@T $@
+$(objpfx)check-installed-headers-c.out: $(+cih-c-iouts)
+	cat $^ > $@; \
+	! grep -qv '^0$$' $(+cih-c-iouts:%=%-ret); \
 	$(evaluate-test)
 
 ifneq "$(CXX)" ""
 tests-special += $(objpfx)check-installed-headers-cxx.out
 libof-check-installed-headers-cxx := testsuite
-$(objpfx)check-installed-headers-cxx.out: \
++cih-cxx-iouts := $(patsubst %,$(objpfx)check-installed-headers-cxx/%.iout,\
+			     $(headers))
+$(+cih-cxx-iouts): $(objpfx)check-installed-headers-cxx/%.iout: \
     scripts/check-installed-headers.sh $(headers)
-	$(SHELL) $(..)scripts/check-installed-headers.sh c++ $(supported-fortify) \
-	  "$(CXX) $(test-config-cxxflags-finput-charset-ascii) \
-	     $(filter-out -std=%,$(CXXFLAGS)) -D_ISOMAC $(+includes)" \
-	  $(headers) > $@; \
+	$(make-target-directory)
+	($(SHELL) $(..)scripts/check-installed-headers.sh c++ $(supported-fortify) \
+	   "$(CXX) $(test-config-cxxflags-finput-charset-ascii) \
+	      $(filter-out -std=%,$(CXXFLAGS)) -D_ISOMAC $(+includes)" \
+	   $*; echo $$? > $@-ret) > $@T; \
+	mv -f $@T $@
+$(objpfx)check-installed-headers-cxx.out: $(+cih-cxx-iouts)
+	cat $^ > $@; \
+	! grep -qv '^0$$' $(+cih-cxx-iouts:%=%-ret); \
 	$(evaluate-test)
 endif # $(CXX)
 
diff --git a/Rules b/Rules
index 385246f07df..a74043e6059 100644
--- a/Rules
+++ b/Rules
@@ -80,15 +80,24 @@ common-generated += dummy.o dummy.c
 
 ifneq "$(headers)" ""
 # Test that all of the headers installed by this directory can be compiled
-# in isolation.
+# in isolation.  Each header gets its own intermediate target so that the
+# it can run concurrently under -j; the .out target concatenates the per-header
+# results in the original $(headers) order.
 tests-special += $(objpfx)check-installed-headers-c.out
 libof-check-installed-headers-c := testsuite
-$(objpfx)check-installed-headers-c.out: \
++cih-c-iouts := $(patsubst %,$(objpfx)check-installed-headers-c/%.iout,\
+			   $(headers))
+$(+cih-c-iouts): $(objpfx)check-installed-headers-c/%.iout: \
     $(..)scripts/check-installed-headers.sh $(headers)
-	$(SHELL) $(..)scripts/check-installed-headers.sh c $(supported-fortify) \
-	  "$(CC) $(test-config-cflags-finput-charset-ascii) \
-	     $(filter-out -std=%,$(CFLAGS)) -D_ISOMAC $(+includes)" \
-	  $(headers) > $@; \
+	$(make-target-directory)
+	($(SHELL) $(..)scripts/check-installed-headers.sh c $(supported-fortify) \
+	   "$(CC) $(test-config-cflags-finput-charset-ascii) \
+	      $(filter-out -std=%,$(CFLAGS)) -D_ISOMAC $(+includes)" \
+	   $*; echo $$? > $@-ret) > $@T; \
+	mv -f $@T $@
+$(objpfx)check-installed-headers-c.out: $(+cih-c-iouts)
+	cat $^ > $@; \
+	! grep -qv '^0$$' $(+cih-c-iouts:%=%-ret); \
 	$(evaluate-test)
 
 ifneq "$(CXX)" ""
@@ -96,12 +105,19 @@ ifneq "$(CXX)" ""
 # in isolation as C++.
 tests-special += $(objpfx)check-installed-headers-cxx.out
 libof-check-installed-headers-cxx := testsuite
-$(objpfx)check-installed-headers-cxx.out: \
++cih-cxx-iouts := $(patsubst %,$(objpfx)check-installed-headers-cxx/%.iout,\
+			     $(headers))
+$(+cih-cxx-iouts): $(objpfx)check-installed-headers-cxx/%.iout: \
     $(..)scripts/check-installed-headers.sh $(headers)
-	$(SHELL) $(..)scripts/check-installed-headers.sh c++ $(supported-fortify) \
-	  "$(CXX) $(test-config-cxxflags-finput-charset-ascii) \
-	     $(filter-out -std=%,$(CXXFLAGS)) -D_ISOMAC $(+includes)" \
-	  $(headers) > $@; \
+	$(make-target-directory)
+	($(SHELL) $(..)scripts/check-installed-headers.sh c++ $(supported-fortify) \
+	   "$(CXX) $(test-config-cxxflags-finput-charset-ascii) \
+	      $(filter-out -std=%,$(CXXFLAGS)) -D_ISOMAC $(+includes)" \
+	   $*; echo $$? > $@-ret) > $@T; \
+	mv -f $@T $@
+$(objpfx)check-installed-headers-cxx.out: $(+cih-cxx-iouts)
+	cat $^ > $@; \
+	! grep -qv '^0$$' $(+cih-cxx-iouts:%=%-ret); \
 	$(evaluate-test)
 endif # $(CXX)
 
-- 
2.43.0