[llvm] cc4beda - [CSSPGO] Adjust SampleContextFrameVector to be a shorter SmallVector

[Hongtao Yu via llvm-commits]

Author: Hongtao Yu
Date: 2022-01-25T21:36:38-08:00
New Revision: cc4beda039ba5441b76b5b112dd5f69553965186

URL: https://github.com/llvm/llvm-project/commit/cc4beda039ba5441b76b5b112dd5f69553965186
DIFF: https://github.com/llvm/llvm-project/commit/cc4beda039ba5441b76b5b112dd5f69553965186.diff

LOG: [CSSPGO] Adjust SampleContextFrameVector to be a shorter SmallVector

It appears that some memory saving can be archived by tweaking the existing `SampleContextFrameVector` setup. Below are memory usage for two benchmarks before and after this change.

1. Medium benchmark:
   - Before:

```
    note: After computeSizeForProfiledFunctions
    note: VM: 12.50 GB   RSS: 11.02 GB
    note: After generateProbeBasedProfile
    note: **VM: 30.56 GB   RSS: 29.08 GB**
    note: After postProcessProfiles
    note: VM: 31.91 GB   RSS: 30.43 GB
```
   - After:

```
    note: After computeSizeForProfiledFunctions
    note: VM: 12.26 GB   RSS: 10.80 GB
    note: After generateProbeBasedProfile
    note: **VM: 28.76 GB   RSS: 27.29 GB**
    note: After postProcessProfiles
    note: VM: 30.12 GB   RSS: 28.66 GB
```

2. Large benchmark:
   - Before:

```
    note: After computeSizeForProfiledFunctions
    note: VM: 106.28 GB   RSS: 91.25 GB
    note: After generateProbeBasedProfile
    note: **VM: 245.19 GB   RSS: 224.30 GB**
    note: After postProcessProfiles
    note: VM: 254.96 GB   RSS: 221.58 GB
```

   - After:

```
    note: After computeSizeForProfiledFunctions
    note: VM: 105.95 GB   RSS: 91.04 GB
    note: After generateProbeBasedProfile
    note: VM: **234.29 GB   RSS: 215.39 GB**
    note: After postProcessProfiles
    note: VM: 244.03 GB   RSS: 213.45 GB
```

Reviewed By: wenlei

Differential Revision: https://reviews.llvm.org/D118203

Added: 
    

Modified: 
    llvm/include/llvm/ProfileData/SampleProf.h

Removed: 
    


################################################################################
diff  --git a/llvm/include/llvm/ProfileData/SampleProf.h b/llvm/include/llvm/ProfileData/SampleProf.h
index 6be54d8d78b2f..bad2139fe8f0e 100644
--- a/llvm/include/llvm/ProfileData/SampleProf.h
+++ b/llvm/include/llvm/ProfileData/SampleProf.h
@@ -450,7 +450,7 @@ static inline hash_code hash_value(const SampleContextFrame &arg) {
                       arg.Location.Discriminator);
 }
 
-using SampleContextFrameVector = SmallVector<SampleContextFrame, 10>;
+using SampleContextFrameVector = SmallVector<SampleContextFrame, 1>;
 using SampleContextFrames = ArrayRef<SampleContextFrame>;
 
 struct SampleContextFrameHash {