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#!/bin/bash
#
# findoptdiff
#
# This script helps find the optimization difference between two llvm
# builds. It is useful when you have a build that is known to work and
# one that exhibits an optimization problem. Identifying the difference
# between the two builds can lead to discovery of the source of a
# mis-optimization.
#
# The script takes two llvm build paths as arguments. These specify the
# the two llvm builds to compare. It is generally expected that they
# are "close cousins". That is, they are the same except that the
# second build contains some experimental optimization features that
# are suspected of producing a misoptimization.
#
# The script takes two bitcode files, one from each build. They are
# presumed to be a compilation of the same program or program fragment
# with the only difference being the builds.
#
# The script operates by iteratively applying the optimizations that gccas
# and gccld run until there is a difference in the assembly resulting
# from the optimization. The difference is then reported with the set of
# optimization passes that produce the difference. The processing
# continues until all optimization passes have been tried. The differences
# for each pass, if they do differ, are placed in a diffs.# file.
#
# To work around differences in the assembly language format, the script
# can also take two filter arguments that post-process the assembly
# so they can be differenced without making false positives for known
# differences in the two builds. These filters are optional.
#
# Usage:
# findoptdiff llvm1 llvm2 bc1 bc2 filter1 filter2
#
# Where:
# llvm1
# is the path to the first llvm build dir
# llvm2
# is the path to the second llvm build dir
# bc1
# is the bitcode file for the first llvm environment
# bc2
# is the bitcode file for the second llvm environment
# filter1
# is an optional filter for filtering the llvm1 generated assembly
# filter2
# is an optional filter for filtering the llvm2 generated assembly
#
llvm1=$1
llvm2=$2
bc1=$3
bc2=$4
filt1=$5
filt2=$6
if [ -z "$filt1" ] ; then
filt1="cat"
fi
if [ -z "$filt2" ] ; then
filt2="cat"
fi
opt1="${bc1}.opt"
opt2="${bc2}.opt"
ll1="${bc1}.ll"
ll2="${bc2}.ll"
opt1ll="${bc1}.opt.ll"
opt2ll="${bc2}.opt.ll"
dis1="$llvm1/Debug/bin/llvm-dis"
dis2="$llvm2/Debug/bin/llvm-dis"
opt1="$llvm1/Debug/bin/opt"
opt2="$llvm2/Debug/bin/opt"
all_switches="-verify -lowersetjmp -simplifycfg -mem2reg -globalopt -globaldce -ipconstprop -deadargelim -instcombine -simplifycfg -prune-eh -inline -simplify-libcalls -argpromotion -tailduplicate -simplifycfg -scalarrepl -instcombine -predsimplify -condprop -tailcallelim -simplifycfg -reassociate -licm -loop-unswitch -instcombine -indvars -loop-unroll -instcombine -load-vn -gcse -sccp -instcombine -condprop -dse -dce -simplifycfg -deadtypeelim -constmerge -internalize -ipsccp -globalopt -constmerge -deadargelim -inline -prune-eh -globalopt -globaldce -argpromotion -instcombine -predsimplify -scalarrepl -globalsmodref-aa -licm -load-vn -gcse -dse -instcombine -simplifycfg -verify"
#counter=0
function tryit {
switches_to_use="$1"
$opt1 $switches_to_use "$bc1" -o - | $dis1 | $filt1 > "$opt1ll"
$opt2 $switches_to_use "$bc2" -o - | $dis2 | $filt2 > "$opt2ll"
diffs="diffs."$((counter++))
diff "$opt1ll" "$opt2ll" > $diffs
if [ $? -ne 0 ] ; then
echo
echo "Diff fails with these switches:"
echo $switches
echo "Differences:"
head $diffs
echo 'Switches:' $switches_to_use >> $diffs
else
rm $diffs
fi
return 1
}
for sw in $all_switches ; do
echo -n " $sw"
switches="$switches $sw"
if tryit "$switches" ; then
break;
fi
done
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