From a9ea00474518545efea1b428eaeb5a1ed67eeba2 Mon Sep 17 00:00:00 2001
From: Alex Richardson <arichardson@FreeBSD.org>
Date: Wed, 15 Jul 2020 12:07:47 +0000
Subject: [PATCH] Avoid rebuilding libpmc in every incremental rebuild

Generate libpmc_events.c in a temporary file first and only overwrite it
if the files are actually different.
This avoids compiling and relinking the different variants of libpmc on
every incremental build.

Reviewed By:	jhb
Differential Revision: https://reviews.freebsd.org/D24784
---
 lib/libpmc/Makefile | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/lib/libpmc/Makefile b/lib/libpmc/Makefile
index 19457880358..0097d5454bc 100644
--- a/lib/libpmc/Makefile
+++ b/lib/libpmc/Makefile
@@ -32,9 +32,13 @@ SUBDIR+= pmu-events
 .endif
 .endif
 
-libpmc_events.c: ${JEVENTS}
-	${JEVENTS} ${EVENT_ARCH} ${.CURDIR}/pmu-events/arch libpmc_events.c
-SRCS+= libpmc_events.c
+libpmc_events.c: ${JEVENTS} .META
+	${JEVENTS} ${EVENT_ARCH} ${.CURDIR}/pmu-events/arch ${.TARGET}.tmp
+	if [ ! -e ${.TARGET} ] || ! cmp -s ${.TARGET} ${.TARGET}.tmp; then \
+		mv -f ${.TARGET}.tmp ${.TARGET}; \
+	fi
+CLEANFILES+=	libpmc_events.c libpmc_events.c.tmp
+SRCS+=	libpmc_events.c
 .endif
 
 WARNS?=	3