From: Willy Tarreau <w@1wt.eu>
Date: Wed, 3 Oct 2018 07:52:51 +0000 (+0200)
Subject: BUILD: Makefile: speed up compiler options detection
X-Git-Tag: v1.9-dev4~90
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=f11ca5e7a43c772637018ec2ad981a9fd7d3816f;p=thirdparty%2Fhaproxy.git

BUILD: Makefile: speed up compiler options detection

Commits b78016649 and d3a7f4035 brought the ability to detect the build
options and warnings that the compiler supports. However, they're detected
using "$(CC) -c", which is 50% slower than "$(CC) -E" for the same result,
just because it starts the assembler at the end. Given that we're starting
to check for a number of warnings, this detection alone starts to become
visible, taking a bit more than 300 ms on the build time. Let's switch to
-E instead to shrink this incompressible time by roughly 100 ms.
---

diff --git a/Makefile b/Makefile
index c4c1f6e799..4eac3f95fd 100644
--- a/Makefile
+++ b/Makefile
@@ -102,13 +102,13 @@
 # Usage: CFLAGS += $(call cc-opt,option). Eg: $(call cc-opt,-fwrapv)
 # Note: ensure the referencing variable is assigned using ":=" and not "=" to
 #       call it only once.
-cc-opt = $(shell set -e; if $(CC) $(1) -c -xc - -o /dev/null </dev/null >&0 2>&0; then echo "$(1)"; fi;)
+cc-opt = $(shell set -e; if $(CC) $(1) -E -xc - -o /dev/null </dev/null >&0 2>&0; then echo "$(1)"; fi;)
 
 # Disable a warning when supported by the compiler. Don't put spaces around the
 # warning! And don't use cc-opt which doesn't always report an error until
 # another one is also returned.
 # Usage: CFLAGS += $(call cc-nowarn,warning). Eg: $(call cc-opt,format-truncation)
-cc-nowarn = $(shell set -e; if $(CC) -W$(1) -c -xc - -o /dev/null </dev/null >&0 2>&0; then echo "-Wno-$(1)"; fi;)
+cc-nowarn = $(shell set -e; if $(CC) -W$(1) -E -xc - -o /dev/null </dev/null >&0 2>&0; then echo "-Wno-$(1)"; fi;)
 
 #### Installation options.
 DESTDIR =