Summary:
Expressions of the form x < 0 ? 0 : x; and x < -1 ? -1 : x can be lowered using bit-operations instead of branching or conditional moves
In thumb-mode this results in a two-instruction sequence, a shift followed by a bic or or while in ARM/thumb2 mode that has flexible second operand the shift can be folded into a single bic/or instructions. In most cases this results in smaller code and possibly less branches, and in no case larger than before.
Patch by Marten Svanfeldt.
Reviewers: fhahn, pbarrio
Reviewed By: pbarrio
Subscribers: efriedma, rogfer01, aemerson, javed.absar, kristof.beyls, llvm-commits
Differential Revision: https://reviews.llvm.org/D42574
llvm-svn: 323869
Constants are crucial for code size in the ARM Thumb-1 instruction
set. The 16 bit instruction size often does not offer enough space
for immediate arguments. This means that additional instructions are
frequently used to load constants into registers. Since constants are
hoisted, this can lead to significant register spillage if they are
used multiple times in a single function. This can be avoided by
rematerialization, i.e. recomputing a constant instead of reloading
it from the stack. This patch fixes the rematerialization of literal
pool loads in the ARM Thumb instruction set.
Patch by Philip Ginsbach
Differential Revision: https://reviews.llvm.org/D33936
llvm-svn: 308004
This update was done with the following bash script:
find test/CodeGen -name "*.ll" | \
while read NAME; do
echo "$NAME"
if ! grep -q "^; *RUN: *llc.*debug" $NAME; then
TEMP=`mktemp -t temp`
cp $NAME $TEMP
sed -n "s/^define [^@]*@\([A-Za-z0-9_]*\)(.*$/\1/p" < $NAME | \
while read FUNC; do
sed -i '' "s/;\(.*\)\([A-Za-z0-9_-]*\):\( *\)$FUNC: *\$/;\1\2-LABEL:\3$FUNC:/g" $TEMP
done
sed -i '' "s/;\(.*\)-LABEL-LABEL:/;\1-LABEL:/" $TEMP
sed -i '' "s/;\(.*\)-NEXT-LABEL:/;\1-NEXT:/" $TEMP
sed -i '' "s/;\(.*\)-NOT-LABEL:/;\1-NOT:/" $TEMP
sed -i '' "s/;\(.*\)-DAG-LABEL:/;\1-DAG:/" $TEMP
mv $TEMP $NAME
fi
done
llvm-svn: 186280
Pablo Barrio