[PATCH] D35804: [BPI] Detect branches in loops that make themselves not taken
John Brawn via Phabricator via llvm-commits
llvm-commits at lists.llvm.org
Mon Jul 24 09:24:50 PDT 2017
john.brawn created this revision.
If we have a loop like this:
int n = 0;
while (...) {
if (++n >= MAX) {
n = 0;
}
}
then the body of the 'if' statement will only be executed once every MAX iterations. Detect this by looking for branches in loops where taking the branch makes the branch condition evaluate to 'not taken' in the next iteration of the loop, and reduce the probability of such branches.
This slightly improves EEMBC benchmarks on cortex-m4/cortex-m33 due to making better choices in if-conversion, but has no effect on any other cpu/benchmark that I could detect.
Repository:
rL LLVM
https://reviews.llvm.org/D35804
Files:
lib/Analysis/BranchProbabilityInfo.cpp
test/Analysis/BranchProbabilityInfo/loop.ll
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