[memprof] Use std::unique_ptr instead of std::optional

[kazutakahirata]

Changing the type of Frame::SymbolName from std::optionalstd::string
to std::uniquestd::string reduces sizeof(Frame) from 64 to 32.

The smaller type reduces the cycle and instruction counts by 23% and
4.4%, respectively, with "llvm-profdata show" modified to deserialize
all MemProfRecords in a MemProf V2 profile. The peak memory usage is
cut down nearly by half.

[llvmbot]

@llvm/pr-subscribers-pgo

Author: Kazu Hirata (kazutakahirata)

Changes

Changing the type of Frame::SymbolName from std::optional<std::string>
to std::unique<std::string> reduces sizeof(Frame) from 64 to 32.

The smaller type reduces the cycle and instruction counts by 23% and
4.4%, respectively, with "llvm-profdata show" modified to deserialize
all MemProfRecords in a MemProf V2 profile. The peak memory usage is
cut down nearly by half.

---

Full diff: https://github.com/llvm/llvm-project/pull/94655.diff

2 Files Affected:

• (modified) llvm/include/llvm/ProfileData/MemProf.h (+9-5)
• (modified) llvm/lib/ProfileData/MemProfReader.cpp (+1-1)

diff --git a/llvm/include/llvm/ProfileData/MemProf.h b/llvm/include/llvm/ProfileData/MemProf.h
index 406144d9db1e8..528abe1ad3d45 100644
--- a/llvm/include/llvm/ProfileData/MemProf.h
+++ b/llvm/include/llvm/ProfileData/MemProf.h
@@ -199,7 +199,7 @@ struct Frame {
   GlobalValue::GUID Function;
   // The symbol name for the function. Only populated in the Frame by the reader
   // if requested during initialization. This field should not be serialized.
-  std::optional<std::string> SymbolName;
+  std::unique_ptr<std::string> SymbolName;
   // The source line offset of the call from the beginning of parent function.
   uint32_t LineOffset;
   // The source column number of the call to help distinguish multiple calls
@@ -210,7 +210,9 @@ struct Frame {
 
   Frame(const Frame &Other) {
     Function = Other.Function;
-    SymbolName = Other.SymbolName;
+    SymbolName = Other.SymbolName
+                     ? std::make_unique<std::string>(*Other.SymbolName)
+                     : nullptr;
     LineOffset = Other.LineOffset;
     Column = Other.Column;
     IsInlineFrame = Other.IsInlineFrame;
@@ -228,7 +230,9 @@ struct Frame {
 
   Frame &operator=(const Frame &Other) {
     Function = Other.Function;
-    SymbolName = Other.SymbolName;
+    SymbolName = Other.SymbolName
+                     ? std::make_unique<std::string>(*Other.SymbolName)
+                     : nullptr;
     LineOffset = Other.LineOffset;
     Column = Other.Column;
     IsInlineFrame = Other.IsInlineFrame;
@@ -237,10 +241,10 @@ struct Frame {
 
   bool operator!=(const Frame &Other) const { return !operator==(Other); }
 
-  bool hasSymbolName() const { return SymbolName.has_value(); }
+  bool hasSymbolName() const { return !!SymbolName; }
 
   StringRef getSymbolName() const {
-    assert(SymbolName.has_value());
+    assert(hasSymbolName());
     return *SymbolName;
   }
 
diff --git a/llvm/lib/ProfileData/MemProfReader.cpp b/llvm/lib/ProfileData/MemProfReader.cpp
index fc3be716087eb..693897f874a29 100644
--- a/llvm/lib/ProfileData/MemProfReader.cpp
+++ b/llvm/lib/ProfileData/MemProfReader.cpp
@@ -690,7 +690,7 @@ Error RawMemProfReader::readNextRecord(
       return F;
     auto Iter = this->GuidToSymbolName.find(F.Function);
     assert(Iter != this->GuidToSymbolName.end());
-    F.SymbolName = Iter->getSecond();
+    F.SymbolName = std::make_unique<std::string>(Iter->getSecond());
     return F;
   };
   return MemProfReader::readNextRecord(GuidRecord, IdToFrameCallback);

[teresajohnson]

from std::optionalstd::string

I assume you have some < and > here but they aren't getting rendered properly. Probably need backticks around the symbols.

[kazutakahirata]

Thank you for reviewing the patch!

from std::optionalstd::string

I assume you have some < and > here but they aren't getting rendered properly. Probably need backticks around the symbols.

Yeah, the github web interface displays these things in a funny way. The actual commit message should be unaffected though.