[TypeProf][InstrFDO]Omit vtable symbols in indexed profiles by default (llvm#96520)

- The indexed iFDO profiles contains compressed vtable names for `llvm-profdata show --show-vtables` debugging 
   usage. An optimized build doesn't need it and doesn't decompress the blob now [1], since optimized binary has the 
   source code and IR to find vtable symbols.
- The motivation is to avoid increasing profile size when it's not necessary.
- This doesn't change the indexed profile format and thereby doesn't need a version change.

[1] https://github.com/llvm/llvm-project/blob/eac925fb81f26342811ad1765e8f9919628e2254/llvm/include/llvm/ProfileData/InstrProfReader.h#L696-L699

Author: mingmingl-llvm

compiler-rt/test/profile/Linux/instrprof-vtable-value-prof.cpp

@@ -12,19 +12,19 @@
 // RUN: llvm-profdata show --function=main --ic-targets --show-vtables %t-test.profraw | FileCheck %s --check-prefixes=COMMON,RAW
 
 // Generate indexed profile from raw profile and show the data.
-// RUN: llvm-profdata merge %t-test.profraw -o %t-test.profdata
+// RUN: llvm-profdata merge --keep-vtable-symbols %t-test.profraw -o %t-test.profdata
 // RUN: llvm-profdata show --function=main --ic-targets --show-vtables %t-test.profdata | FileCheck %s --check-prefixes=COMMON,INDEXED
 
 // Generate text profile from raw and indexed profiles respectively and show the data.
-// RUN: llvm-profdata merge --text %t-test.profraw -o %t-raw.proftext
+// RUN: llvm-profdata merge --keep-vtable-symbols --text %t-test.profraw -o %t-raw.proftext
 // RUN: llvm-profdata show --function=main --ic-targets --show-vtables --text %t-raw.proftext | FileCheck %s --check-prefix=ICTEXT
-// RUN: llvm-profdata merge --text %t-test.profdata -o %t-indexed.proftext
+// RUN: llvm-profdata merge --keep-vtable-symbols --text %t-test.profdata -o %t-indexed.proftext
 // RUN: llvm-profdata show --function=main --ic-targets --show-vtables --text %t-indexed.proftext | FileCheck %s --check-prefix=ICTEXT
 
 // Generate indexed profile from text profiles and show the data
-// RUN: llvm-profdata merge --binary %t-raw.proftext -o %t-text.profraw
+// RUN: llvm-profdata merge --keep-vtable-symbols --binary %t-raw.proftext -o %t-text.profraw
 // RUN: llvm-profdata show --function=main --ic-targets --show-vtables %t-text.profraw | FileCheck %s --check-prefixes=COMMON,INDEXED
-// RUN: llvm-profdata merge --binary %t-indexed.proftext -o %t-text.profdata
+// RUN: llvm-profdata merge --keep-vtable-symbols --binary %t-indexed.proftext -o %t-text.profdata
 // RUN: llvm-profdata show --function=main --ic-targets --show-vtables %t-text.profdata | FileCheck %s --check-prefixes=COMMON,INDEXED
 
 // COMMON: Counters:

llvm/test/tools/llvm-profdata/vtable-value-prof.test

@@ -1,7 +1,7 @@
 ; RUN: rm -rf %t && mkdir %t && cd %t
 
 ; Generate indexed profiles from text profiles
-RUN: llvm-profdata merge %S/Inputs/vtable-value-prof.proftext -o indexed.profdata
+RUN: llvm-profdata merge --keep-vtable-symbols %S/Inputs/vtable-value-prof.proftext -o indexed.profdata
 
 ; Show indexed profiles
 RUN: llvm-profdata show --function=main --ic-targets --show-vtables indexed.profdata | FileCheck %s --check-prefix=INDEXED
@@ -10,7 +10,7 @@ RUN: llvm-profdata show --function=main --ic-targets --show-vtables indexed.prof
 RUN: llvm-profdata show --function=main --ic-targets --show-vtables --text %S/Inputs/vtable-value-prof.proftext | FileCheck %s --check-prefix=ICTEXT
 
 ; Convert indexed profiles to its textual output and show it.
-RUN: llvm-profdata merge --text -o text-from-indexed.proftext indexed.profdata
+RUN: llvm-profdata merge --keep-vtable-symbols --text -o text-from-indexed.proftext indexed.profdata
 RUN: llvm-profdata show --function=main --ic-targets --show-vtables text-from-indexed.proftext | FileCheck %s --check-prefix=INDEXED
 RUN: llvm-profdata show --function=main --ic-targets --show-vtables --text text-from-indexed.proftext | FileCheck %s --check-prefix=ICTEXT
 

llvm/tools/llvm-profdata/llvm-profdata.cpp

@@ -291,6 +291,11 @@ cl::opt<bool> DropProfileSymbolList(
     cl::desc("Drop the profile symbol list when merging AutoFDO profiles "
              "(only meaningful for -sample)"));
 
+cl::opt<bool> KeepVTableSymbols(
+    "keep-vtable-symbols", cl::init(false), cl::Hidden,
+    cl::sub(MergeSubcommand),
+    cl::desc("If true, keep the vtable symbols in indexed profiles"));
+
 // Temporary support for writing the previous version of the format, to enable
 // some forward compatibility.
 // TODO: Consider enabling this with future version changes as well, to ease
@@ -767,11 +772,12 @@ static void loadInput(const WeightedFile &Input, SymbolRemapper *Remapper,
     });
   }
 
-  const InstrProfSymtab &symtab = Reader->getSymtab();
-  const auto &VTableNames = symtab.getVTableNames();
+  if (KeepVTableSymbols) {
+    const InstrProfSymtab &symtab = Reader->getSymtab();
+    const auto &VTableNames = symtab.getVTableNames();
 
-  for (const auto &kv : VTableNames) {
-    WC->Writer.addVTableName(kv.getKey());
+    for (const auto &kv : VTableNames)
+      WC->Writer.addVTableName(kv.getKey());
   }
 
   if (Reader->hasTemporalProfile()) {