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2016 Dec 26
1
Multiple simplifycfg pass make some loop significantly slower
...st clang-3.8 and clang-4.0 nightly. Depending on where I put the
"increment" code for a for-loop, I can get 2x performance difference.
The slow (but natural) version:
for (i=0; i<size; ++i) {
ai = arr[i];
if ( ai <= amin ) {
amin = ai;
all_missing = 0;
}
}
The fast version:
for (i=0; i<size;) {
ai = arr[i];
++i; // increment moved here
if ( ai <= amin ) {
amin = ai;
all_missing = 0;
}
}
With the fast version, adding a dummy line after the if-block...