From 489377c0a4d07d3ea957657d39f45aa77ed04673 Mon Sep 17 00:00:00 2001
From: Alex Richardson <arichardson@FreeBSD.org>
Date: Wed, 26 Aug 2020 10:21:38 +0000
Subject: [PATCH] Avoid recomputing COMPILER_/LINKER_ variables when set
 explicitly

I noticed that when we build libraries for a different ABI (in CheriBSD) we
were calling ${XCC}/${LD} --version for every directory. It turns out that
this was caused by bsd.compat.mk explicitly setting (X_)COMPILER variables
for that build stage and this stops the _can_export logic from working.
To fix this, we change the check to only set _can_export=no if the variable
is set and it is set to a different value than the cached value.
This noticeably speeds up the tree walk while building compat libraries.
During an upstream amd64 buildworld this also removes 8 --version calls.

Obtained from:	CheriBSD
Reviewed By:	brooks, emaste
Differential Revision: https://reviews.freebsd.org/D25986
---
 share/mk/bsd.compiler.mk | 7 +++++--
 share/mk/bsd.linker.mk   | 7 +++++--
 2 files changed, 10 insertions(+), 4 deletions(-)

diff --git a/share/mk/bsd.compiler.mk b/share/mk/bsd.compiler.mk
index ffea2c9e1254..0345ab9395ed 100644
--- a/share/mk/bsd.compiler.mk
+++ b/share/mk/bsd.compiler.mk
@@ -146,10 +146,13 @@ _exported_vars=	${X_}COMPILER_TYPE ${X_}COMPILER_VERSION \
 		${X_}COMPILER_FREEBSD_VERSION ${X_}COMPILER_RESOURCE_DIR
 ${X_}_cc_hash=	${${cc}}${MACHINE}${PATH}
 ${X_}_cc_hash:=	${${X_}_cc_hash:hash}
-# Only import if none of the vars are set somehow else.
+# Only import if none of the vars are set differently somehow else.
 _can_export=	yes
 .for var in ${_exported_vars}
-.if defined(${var})
+.if defined(${var}) && (!defined(${var}__${${X_}_cc_hash}) || ${${var}__${${X_}_cc_hash}} != ${${var}})
+.if defined(${var}__${${X_}_ld_hash})
+.info "Cannot import ${X_}COMPILER variables since cached ${var} is different: ${${var}__${${X_}_cc_hash}} != ${${var}}"
+.endif
 _can_export=	no
 .endif
 .endfor
diff --git a/share/mk/bsd.linker.mk b/share/mk/bsd.linker.mk
index ae867502c6f2..344a5b937380 100644
--- a/share/mk/bsd.linker.mk
+++ b/share/mk/bsd.linker.mk
@@ -41,10 +41,13 @@ _exported_vars=	${X_}LINKER_TYPE ${X_}LINKER_VERSION ${X_}LINKER_FEATURES \
 		${X_}LINKER_FREEBSD_VERSION
 ${X_}_ld_hash=	${${ld}}${MACHINE}${PATH}
 ${X_}_ld_hash:=	${${X_}_ld_hash:hash}
-# Only import if none of the vars are set somehow else.
+# Only import if none of the vars are set differently somehow else.
 _can_export=	yes
 .for var in ${_exported_vars}
-.if defined(${var})
+.if defined(${var}) && (!defined(${var}__${${X_}_ld_hash}) || ${${var}__${${X_}_ld_hash}} != ${${var}})
+.if defined(${var}__${${X_}_ld_hash})
+.info "Cannot import ${X_}LINKER variables since cached ${var} is different: ${${var}__${${X_}_ld_hash}} != ${${var}}"
+.endif
 _can_export=	no
 .endif
 .endfor