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configure: replace -Os with equivalent based on -O2 

aside from the documented differences, which are the contents of this
patch, GCC's -Os also has hard-coded unwanted behaviors which are
impossible to override, like refusing to strength-reduce division by a
constant to multiplication, presumably because the div saves a couple
bytes of code. for this reason, getting rid of -Os and switching to an
equivalent default optimization profile based on -O2 has been a
long-term goal.

as follow-ups, it may make sense to evaluate which of these variations
from -O2 actually do anything useful, and eliminate the ones which are
not helpful or which throw away performance for insignificant size
savings. but for now, I've replicated -Os as closely as possible to
provide a baseline for such evaluation.
This commit is contained in:
Rich Felker 2023-05-21 12:16:11 -04:00
parent 718f363bc2
commit b90841e258
1 changed files with 14 additions and 1 deletions
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15
configure vendored
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@ -444,7 +444,20 @@ xno|x) printf "disabled\n" ; optimize=no ;;
*) printf "custom\n" ;;
esac
test "$optimize" = no || tryflag CFLAGS_AUTO -Os || tryflag CFLAGS_AUTO -O2
if test "$optimize" = no ; then :
else
tryflag CFLAGS_AUTO -O2
tryflag CFLAGS_AUTO -fno-align-jumps
tryflag CFLAGS_AUTO -fno-align-functions
tryflag CFLAGS_AUTO -fno-align-loops
tryflag CFLAGS_AUTO -fno-align-labels
tryflag CFLAGS_AUTO -fira-region=one
tryflag CFLAGS_AUTO -fira-hoist-pressure
tryflag CFLAGS_AUTO -freorder-blocks-algorithm=simple \
|| tryflag CFLAGS_AUTO -fno-reorder-blocks
tryflag CFLAGS_AUTO -fno-prefetch-loop-arrays
tryflag CFLAGS_AUTO -fno-tree-ch
fi
test "$optimize" = yes && optimize="internal,malloc,string"
if fnmatch 'no|size' "$optimize" ; then :