[PATCH] D22696: [CodeGenPrep] Skip merging empty case blocks

[Jun Bum Lim via llvm-commits]

junbuml added a comment.

As of now, with/without this change (with FreqRatio=2), I can see  6.7% more https://reviews.llvm.org/L1 I-cache miss from perf-stat. I didn’t try to narrow down to the place in which the regression was caused, but I printed out FreqRatio, NumCopyInsertionPHIs, and NumOfCases when this change applied and I can see this was applied even when the number of cases in switch is small enough due to the aggressive FreqRatio=2.  Please let me know if you want me to further narrow down.

FreqRatio: 160 , NumCopyInsertionPHIs : 1, NumCase: 5
FreqRatio: 102 , NumCopyInsertionPHIs : 1, NumCase: 3
FreqRatio: 786 , NumCopyInsertionPHIs : 16, NumCase: 793
FreqRatio: 64 , NumCopyInsertionPHIs : 1, NumCase: 2
FreqRatio: 128 , NumCopyInsertionPHIs : 1, NumCase: 4
FreqRatio: 128 , NumCopyInsertionPHIs : 0, NumCase: 4
FreqRatio: 128 , NumCopyInsertionPHIs : 0, NumCase: 4
FreqRatio: 128 , NumCopyInsertionPHIs : 0, NumCase: 4
FreqRatio: 128 , NumCopyInsertionPHIs : 0, NumCase: 4
FreqRatio: 128 , NumCopyInsertionPHIs : 0, NumCase: 4
FreqRatio: 128 , NumCopyInsertionPHIs : 0, NumCase: 4
FreqRatio: 128 , NumCopyInsertionPHIs : 0, NumCase: 4
FreqRatio: 128 , NumCopyInsertionPHIs : 0, NumCase: 4
FreqRatio: 8 , NumCopyInsertionPHIs : 5, NumCase: 7
FreqRatio: 8 , NumCopyInsertionPHIs : 5, NumCase: 7
FreqRatio: 8 , NumCopyInsertionPHIs : 5, NumCase: 7
FreqRatio: 8 , NumCopyInsertionPHIs : 5, NumCase: 7
FreqRatio: 8 , NumCopyInsertionPHIs : 5, NumCase: 7
FreqRatio: 8 , NumCopyInsertionPHIs : 5, NumCase: 7
FreqRatio: 8 , NumCopyInsertionPHIs : 5, NumCase: 7
FreqRatio: 8 , NumCopyInsertionPHIs : 5, NumCase: 7
FreqRatio: 8 , NumCopyInsertionPHIs : 5, NumCase: 7
FreqRatio: 8 , NumCopyInsertionPHIs : 5, NumCase: 7
FreqRatio: 32 , NumCopyInsertionPHIs : 1, NumCase: 7
FreqRatio: 32 , NumCopyInsertionPHIs : 1, NumCase: 8
FreqRatio: 32 , NumCopyInsertionPHIs : 3, NumCase: 4
FreqRatio: 96 , NumCopyInsertionPHIs : 0, NumCase: 3
FreqRatio: 64 , NumCopyInsertionPHIs : 0, NumCase: 2
FreqRatio: 39 , NumCopyInsertionPHIs : 0, NumCase: 32
FreqRatio: 1024 , NumCopyInsertionPHIs : 0, NumCase: 32
FreqRatio: 1024 , NumCopyInsertionPHIs : 0, NumCase: 32
FreqRatio: 39 , NumCopyInsertionPHIs : 1, NumCase: 32
FreqRatio: 864 , NumCopyInsertionPHIs : 0, NumCase: 27
FreqRatio: 32 , NumCopyInsertionPHIs : 0, NumCase: 2
FreqRatio: 64 , NumCopyInsertionPHIs : 1, NumCase: 3
FreqRatio: 64 , NumCopyInsertionPHIs : 1, NumCase: 3
FreqRatio: 64 , NumCopyInsertionPHIs : 1, NumCase: 3
FreqRatio: 64 , NumCopyInsertionPHIs : 1, NumCase: 3
FreqRatio: 193 , NumCopyInsertionPHIs : 1, NumCase: 6


https://reviews.llvm.org/D22696