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salam
2016 Dec 26
1
Multiple simplifycfg pass make some loop significantly slower
Hi all,
I am noticing a significant degradation in execution performance in loops
with just one backedge than loops with two backedges. Unifying the
backedges into one will also cause the slowdown.
To replicate this problem, I used the C code in
https://gist.github.com/sklam/11f11a410258ca191e6f263262a4ea65 and checked
against 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...