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| author | Dehao Chen <dehao@google.com> | 2016-06-08 21:30:12 +0000 |
|---|---|---|
| committer | Dehao Chen <dehao@google.com> | 2016-06-08 21:30:12 +0000 |
| commit | 769219b11afaefa6e5526d439e45a031a93db85d (patch) | |
| tree | b9ac024bc091b7320b44decbc41cca8512e987bb /llvm/lib/Transforms/Scalar/EarlyCSE.cpp | |
| parent | 96c63abad87714ebc7e7a531297a89b54d5f24de (diff) | |
| download | bcm5719-llvm-769219b11afaefa6e5526d439e45a031a93db85d.tar.gz bcm5719-llvm-769219b11afaefa6e5526d439e45a031a93db85d.zip | |
Revive http://reviews.llvm.org/D12778 to handle forward-hot-prob and backward-hot-prob consistently.
Summary:
Consider the following diamond CFG:
A
/ \
B C
\/
D
Suppose A->B and A->C have probabilities 81% and 19%. In block-placement, A->B is called a hot edge and the final placement should be ABDC. However, the current implementation outputs ABCD. This is because when choosing the next block of B, it checks if Freq(C->D) > Freq(B->D) * 20%, which is true (if Freq(A) = 100, then Freq(B->D) = 81, Freq(C->D) = 19, and 19 > 81*20%=16.2). Actually, we should use 25% instead of 20% as the probability here, so that we have 19 < 81*25%=20.25, and the desired ABDC layout will be generated.
Reviewers: djasper, davidxl
Subscribers: llvm-commits
Differential Revision: http://reviews.llvm.org/D20989
llvm-svn: 272203
Diffstat (limited to 'llvm/lib/Transforms/Scalar/EarlyCSE.cpp')
0 files changed, 0 insertions, 0 deletions
