meson: Add support for building with precompiled headers

This substantially speeds up building for windows, due to the vast amount of
headers included via windows.h. A cross build from linux targetting mingw goes
from

994.11user 136.43system 0:31.58elapsed 3579%CPU
to
422.41user 89.05system 0:14.35elapsed 3562%CPU

The wins on windows are similar-ish (but I don't have a system at hand just
now for actual numbers). Targetting other operating systems the wins are far
smaller (tested linux, macOS, FreeBSD).

For now precompiled headers are disabled by default, it's not clear how well
they work on all platforms. E.g. on FreeBSD gcc doesn't seem to have working
support, but clang does.

When doing a full build precompiled headers are only beneficial for targets
with multiple .c files, as meson builds a separate precompiled header for each
target (so that different compilation options take effect). This commit
therefore only changes target with at least two .c files to use precompiled
headers.

Because this commit adds b_pch=false to the default_options new build
directories will have precompiled headers disabled by default, however
existing build directories will continue use the default value of b_pch, which
is true.

Note that using precompiled headers with ccache requires setting
CCACHE_SLOPPINESS=pch_defines,time_macros to get hits.

Reviewed-by: Peter Eisentraut <[email protected]>
Reviewed-by: Justin Pryzby <[email protected]>
Discussion: https://postgr.es/m/CA+hUKG+50eOUbN++ocDc0Qnp9Pvmou23DSXu=ZA6fepOcftKqA@mail.gmail.com
Discussion: https://postgr.es/m/[email protected]
Discussion: https://postgr.es/m/20190826054000.GE7005%40paquier.xyz

8 files changed, 8 insertions, 0 deletions

diff --git a/contrib/bloom/meson.build b/contrib/bloom/meson.build
index 16f3b83e4d2..163a93c98fb 100644
--- a/contrib/bloom/meson.build
+++ b/contrib/bloom/meson.build
@@ -15,6 +15,7 @@ endif
 
 bloom = shared_module('bloom',
   bloom_sources,
+  c_pch: pch_postgres_h,
   kwargs: contrib_mod_args,
 )
 contrib_targets += bloom
diff --git a/contrib/btree_gist/meson.build b/contrib/btree_gist/meson.build
index e98c91dacc8..bfb7865d213 100644
--- a/contrib/btree_gist/meson.build
+++ b/contrib/btree_gist/meson.build
@@ -33,6 +33,7 @@ endif
 
 btree_gist = shared_module('btree_gist',
   btree_gist_sources,
+  c_pch: pch_postgres_h,
   kwargs: contrib_mod_args,
 )
 contrib_targets += btree_gist
diff --git a/contrib/hstore/meson.build b/contrib/hstore/meson.build
index 2bb26bb772b..a2a4ec36cb0 100644
--- a/contrib/hstore/meson.build
+++ b/contrib/hstore/meson.build
@@ -18,6 +18,7 @@ endif
 
 hstore = shared_module('hstore',
   hstore_sources,
+  c_pch: pch_postgres_h,
   kwargs: contrib_mod_args,
 )
 contrib_targets += hstore
diff --git a/contrib/pg_trgm/meson.build b/contrib/pg_trgm/meson.build
index c8c7c07b308..839d6c4a7f6 100644
--- a/contrib/pg_trgm/meson.build
+++ b/contrib/pg_trgm/meson.build
@@ -13,6 +13,7 @@ endif
 
 pg_trgm = shared_module('pg_trgm',
   pg_trgm_sources,
+  c_pch: pch_postgres_h,
   kwargs: contrib_mod_args,
 )
 contrib_targets += pg_trgm
diff --git a/contrib/pgcrypto/meson.build b/contrib/pgcrypto/meson.build
index 7fc7bbc7ca1..cc782578b49 100644
--- a/contrib/pgcrypto/meson.build
+++ b/contrib/pgcrypto/meson.build
@@ -78,6 +78,7 @@ endif
 pgcrypto = shared_module('pgcrypto',
   pgcrypto_sources,
   link_with: pgcrypto_link_with,
+  c_pch: pch_postgres_h,
   kwargs: contrib_mod_args + {
     'dependencies': [pgcrypto_deps, contrib_mod_args['dependencies']]
   },
diff --git a/contrib/pgstattuple/meson.build b/contrib/pgstattuple/meson.build
index 05e4cd46a5c..42d0b0e6ce9 100644
--- a/contrib/pgstattuple/meson.build
+++ b/contrib/pgstattuple/meson.build
@@ -12,6 +12,7 @@ endif
 
 pgstattuple = shared_module('pgstattuple',
   pgstattuple_sources,
+  c_pch: pch_postgres_h,
   kwargs: contrib_mod_args,
 )
 contrib_targets += pgstattuple
diff --git a/contrib/sepgsql/meson.build b/contrib/sepgsql/meson.build
index 8bef239e3c2..1ac0fa388ab 100644
--- a/contrib/sepgsql/meson.build
+++ b/contrib/sepgsql/meson.build
@@ -22,6 +22,7 @@ endif
 
 sepgsql = shared_module('sepgsql',
   sepgsql_sources,
+  c_pch: pch_postgres_h,
   kwargs: contrib_mod_args + {
     'dependencies': [selinux, contrib_mod_args['dependencies']],
   }
diff --git a/contrib/xml2/meson.build b/contrib/xml2/meson.build
index 89b0d677516..92ab3368428 100644
--- a/contrib/xml2/meson.build
+++ b/contrib/xml2/meson.build
@@ -15,6 +15,7 @@ endif
 
 xml2 = shared_module('pgxml',
   xml2_sources,
+  c_pch: pch_postgres_h,
   kwargs: contrib_mod_args + {
     'dependencies': [libxml, libxslt, contrib_mod_args['dependencies']],
   },