pythongh-128042: Emit a configure warning when -O0 and --enable-optimizations are combined (python#137975)

taegyunkim · AA-Turner · web-flow · commit ffaec6e2a11f · 2025-08-27T01:00:43.000+02:00
Co-authored-by: Adam Turner &lt;9087854+AA-Turner@users.noreply.github.com&gt;
diff --git a/Misc/NEWS.d/next/Build/2025-08-26-21-18-32.gh-issue-128042.5voC8H.rst b/Misc/NEWS.d/next/Build/2025-08-26-21-18-32.gh-issue-128042.5voC8H.rst
@@ -0,0 +1 @@
+``./configure`` now warns when ``--enable-optimizations`` and ``CFLAGS=-O0`` are both set, suggesting removing ``-O0`` from ``CFLAGS`` for optimal performance.  Patch by Taegyun Kim.
diff --git a/configure b/configure
diff --git a/configure.ac b/configure.ac
@@ -1823,6 +1823,14 @@ fi],
 [AC_MSG_RESULT([no])])
 
 if test "$Py_OPT" = 'true' ; then
+  # Check for conflicting CFLAGS=-O0 and --enable-optimizations
+  case "$CFLAGS" in
+    *-O0*)
+      AC_MSG_WARN([m4_normalize([
+        CFLAGS contains -O0 which may conflict with --enable-optimizations.
+        Consider removing -O0 from CFLAGS for optimal performance.])])
+      ;;
+  esac
   # Intentionally not forcing Py_LTO='true' here.  Too many toolchains do not
   # compile working code using it and both test_distutils and test_gdb are
   # broken when you do manage to get a toolchain that works with it.  People

Original file line number	Diff line number	Diff line change
`@@ -0,0 +1 @@`
	`1`	+``./configure`` now warns when ``--enable-optimizations`` and ``CFLAGS=-O0`` are both set, suggesting removing ``-O0`` from ``CFLAGS`` for optimal performance. Patch by Taegyun Kim.