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rules.mak: speedup save-vars load-vars

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Unnesting variables spends a lot of time parsing and executing foreach
and if functions.  Because actually very few variables have to be
saved and restored, a good strategy is to remember what has to be done
in load-vars, and only iterate the right variables in load-vars.
For save-vars, unroll the foreach loop to provide another small
improvement.

This speeds up a "noop" build from around 15.5 seconds on my laptop
to 11.7 (25% roughly).

Reviewed-by: Fam Zheng <famz@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Paolo Bonzini 2016-11-02 16:10:23 +01:00
parent eb7a20a361
commit 5ffb350541
1 changed files with 10 additions and 12 deletions
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22
rules.mak
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@ -192,15 +192,15 @@ clean: clean-timestamp
# save-vars
# Usage: $(call save-vars, vars)
# Save each variable $v in $vars as save-vars-$v, save their object's
# variables, then clear $v.
# variables, then clear $v. saved-vars-$v contains the variables that
# where saved for the objects, in order to speedup load-vars.
define save-vars
$(foreach v,$1,
$(eval save-vars-$v := $(value $v))
$(foreach o,$($v),
$(foreach k,cflags libs objs,
$(if $($o-$k),
$(eval save-vars-$o-$k := $($o-$k))
$(eval $o-$k := ))))
$(eval saved-vars-$v := $(foreach o,$($v), \
$(if $($o-cflags), $o-cflags $(eval save-vars-$o-cflags := $($o-cflags))$(eval $o-cflags := )) \
$(if $($o-libs), $o-libs $(eval save-vars-$o-libs := $($o-libs))$(eval $o-libs := )) \
$(if $($o-objs), $o-objs $(eval save-vars-$o-objs := $($o-objs))$(eval $o-objs := ))))
$(eval $v := ))
endef
@ -213,12 +213,10 @@ define load-vars
$(eval $2-new-value := $(value $2))
$(foreach v,$1,
$(eval $v := $(value save-vars-$v))
$(foreach o,$($v),
$(foreach k,cflags libs objs,
$(if $(save-vars-$o-$k),
$(eval $o-$k := $(save-vars-$o-$k))
$(eval save-vars-$o-$k := ))))
$(eval save-vars-$v := ))
$(foreach o,$(saved-vars-$v),
$(eval $o := $(save-vars-$o)) $(eval save-vars-$o := ))
$(eval save-vars-$v := )
$(eval saved-vars-$v := ))
$(eval $2 := $(value $2) $($2-new-value))
endef