meson: re-enable -Wmaybe-uninitialized on -O[02] with recent gcc versions

The warning was disabled in 8794164fed5f0142c34358613f92f4f761af4edd to avoid
false positives. But it is useful in finding errors, even if it sometimes
results in untrue warnings (c.f. 77fac974fe, da46a1bc3c).

After #19168, #19169, and #19175, there are no warnings with
-Dbuildtype=debug-optimized/-O2 and gcc-11.0.1-0.3.fc34.x86_64. Warnings
are reenabled for -O[23]

-O0 is good for development, and -O2 is the default optimization level for
Fedora package builds. -Os, -O3, -O1, and -Og still generate some warnings. In
fact, with -Os the number of warnings seems completely hopeless. Dozens and
dozens.

diff --git a/meson.build b/meson.build
index 2d44e7948dde49df597e3a6e7a151e7cb4bbcdd5..a8976c203745206e94989443371eeb6d837797df 100644 (file)
--- a/meson.build
+++ b/meson.build
@@ -395,10 +395,6 @@ possible_cc_flags = [
         '-Wno-error=#warnings',  # clang
         '-Wno-string-plus-int',  # clang
 
-        # Disable -Wmaybe-uninitialized, since it's noisy on gcc 8 with
-        # optimizations enabled, producing essentially false positives.
-        '-Wno-maybe-uninitialized',
-
         '-ffast-math',
         '-fno-common',
         '-fdiagnostics-show-option',
@@ -409,6 +405,15 @@ possible_cc_flags = [
         '--param=ssp-buffer-size=4',
 ]
 
+# Disable -Wmaybe-unitialized when compiling with -Os/-O1/-O3/etc. There are
+# too many false positives with gcc >= 8. Effectively, we only test with -O0
+# and -O2; this should be enough to catch most important cases without too much
+# busywork. See https://github.com/systemd/systemd/pull/19226.
+if cc.get_id() == 'gcc' and (not '02'.contains(get_option('optimization')) or
+                             cc.version().version_compare('<10'))
+        possible_cc_flags += '-Wno-maybe-uninitialized'
+endif
+
 # --as-needed and --no-undefined are provided by meson by default,
 # run mesonconf to see what is enabled
 possible_link_flags = [