[SampleFDO] Add a cutoff flag to control how many symbols will be included into profile symbol list.

[wmi]

Summary

When test is unrepresentative to production behavior, sample profile collected from production can cause unexpected performance behavior in test. To triage such issue, it is useful to have a cutoff flag to control how many symbols will be included into profile symbol list for binary search.

[tejohnson]

llvm/lib/ProfileData/SampleProf.cpp

34

Nit: suggest making "cutoff" one word not hyphenated in option.

llvm/test/Transforms/SampleProfile/profile-sample-accurate.ll

66

Shouldn't it be the other way around - i.e. with the larger cutoff it will be included and with the smaller one it isn't?

Also - confused at how the cutoff correlates to the placement in profile-symbol-list.text. In that file, _Z3toov is symbol number 5. So wouldn't a cutoff of 4 vs 5 affect whether it is included?

[davidxl]

llvm/test/Transforms/SampleProfile/profile-sample-accurate.ll

66

I think it is sorted list.

When cutoff is 3, precise symbol list includes too, so too has profile of 0.

[wmi]

llvm/lib/ProfileData/SampleProf.cpp

34

Fixed.

llvm/test/Transforms/SampleProfile/profile-sample-accurate.ll

66

Nice catch. It should be the other way around. I fix it.

Yes, the order is confusing. David's explanation is right. It is sorted when the text profile symbol list is written into binary section. I change the order in the text to remove the confusion.

[wmi]

Address Teresa's comment.

[tejohnson]

lgtm

llvm/lib/ProfileData/SampleProf.cpp

 //
 //===----------------------------------------------------------------------===//
 
 #include "llvm/ProfileData/SampleProf.h"
 #include "llvm/Config/llvm-config.h"
 #include "llvm/IR/DebugInfoMetadata.h"
 #include "llvm/IR/PseudoProbe.h"
 #include "llvm/ProfileData/SampleProfReader.h"
+#include "llvm/Support/CommandLine.h"
 #include "llvm/Support/Compiler.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/Error.h"
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/LEB128.h"
 #include "llvm/Support/ManagedStatic.h"
 #include "llvm/Support/raw_ostream.h"
 #include <string>
 #include <system_error>
 
 using namespace llvm;
 using namespace sampleprof;
 
+static cl::opt<uint64_t> ProfileSymbolListCutOff(
+    "profile-symbol-list-cut-off", cl::Hidden, cl::init(-1), cl::ZeroOrMore,
+    cl::desc("Cutoff value about how many symbols in profile symbol list "
+             "will be used. This is very useful for performance debugging"));
+
 namespace llvm {
 namespace sampleprof {
 SampleProfileFormat FunctionSamples::Format;
 bool FunctionSamples::ProfileIsProbeBased = false;
 bool FunctionSamples::ProfileIsCS = false;
 bool FunctionSamples::UseMD5;
 } // namespace sampleprof
 } // namespace llvm

 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
 LLVM_DUMP_METHOD void FunctionSamples::dump() const { print(dbgs(), 0); }
 #endif
 
 std::error_code ProfileSymbolList::read(const uint8_t *Data,
                                         uint64_t ListSize) {
   const char *ListStart = reinterpret_cast<const char *>(Data);
   uint64_t Size = 0;
-  while (Size < ListSize) {
+  uint64_t StrNum = 0;
+  while (Size < ListSize && StrNum < ProfileSymbolListCutOff) {
     StringRef Str(ListStart + Size);
     add(Str);
     Size += Str.size() + 1;
+    StrNum++;
   }
-  if (Size != ListSize)
+  if (Size != ListSize && StrNum != ProfileSymbolListCutOff)
     return sampleprof_error::malformed;
   return sampleprof_error::success;
 }
 
 std::error_code ProfileSymbolList::write(raw_ostream &OS) {
   // Sort the symbols before output. If doing compression.
   // It will make the compression much more effective.
   std::vector<StringRef> SortedList(Syms.begin(), Syms.end());

llvm/test/Transforms/SampleProfile/Inputs/profile-symbol-list.text

 _Z3goov
 _Z3sumii
 __libc_csu_fini
 __libc_csu_init
+_Z3toov
 _dl_relocate_static_pie
 _fini
 _init
 _start
 main

llvm/test/Transforms/SampleProfile/profile-sample-accurate.ll

 ; RUN: opt < %s -sample-profile -sample-profile-file=%S/Inputs/profsampleacc.extbinary.afdo -profile-summary-cutoff-hot=600000 -profile-sample-accurate -enable-new-pm=0 -S | FileCheck %s --check-prefix=CALL_SUM_IS_WARM
 ; RUN: opt < %s -passes=sample-profile -sample-profile-file=%S/Inputs/profsampleacc.extbinary.afdo -profile-summary-cutoff-hot=900000 -profile-sample-accurate -S | FileCheck %s --check-prefix=CALL_SUM_IS_HOT
 ; RUN: opt < %s -sample-profile -sample-profile-file=%S/Inputs/profsampleacc.extbinary.afdo -profile-summary-cutoff-hot=600000 -profile-sample-accurate -enable-new-pm=0 -S | FileCheck %s --check-prefix=CALL_SUM_IS_WARM
 ; RUN: opt < %s -passes=sample-profile -sample-profile-file=%S/Inputs/profsampleacc.extbinary.afdo -profile-summary-cutoff-hot=900000 -profile-sample-accurate -S | FileCheck %s --check-prefix=CALL_SUM_IS_HOT
 
 ; RUN: llvm-profdata merge -sample -extbinary -prof-sym-list=%S/Inputs/profile-symbol-list.text %S/Inputs/profsampleacc.extbinary.afdo -o %t.symlist.afdo
 ; RUN: opt < %s -sample-profile -sample-profile-file=%t.symlist.afdo -profile-summary-cutoff-hot=600000 -profile-accurate-for-symsinlist -enable-new-pm=0 -S | FileCheck %s --check-prefix=PROFSYMLIST
 ; RUN: opt < %s -passes=sample-profile -sample-profile-file=%t.symlist.afdo -profile-summary-cutoff-hot=600000 -profile-accurate-for-symsinlist -S | FileCheck %s --check-prefix=PROFSYMLIST
+; RUN: opt < %s -passes=sample-profile -sample-profile-file=%t.symlist.afdo -profile-accurate-for-symsinlist -profile-symbol-list-cut-off=2 -S | FileCheck %s --check-prefix=PSLCUTOFF2
+; RUN: opt < %s -passes=sample-profile -sample-profile-file=%t.symlist.afdo -profile-accurate-for-symsinlist -profile-symbol-list-cut-off=3 -S | FileCheck %s --check-prefix=PSLCUTOFF3
 ;
 ; If -profile-accurate-for-symsinlist and -profile-sample-accurate both present,
 ; -profile-sample-accurate will override -profile-accurate-for-symsinlist.
 ; RUN: opt < %s -sample-profile -sample-profile-file=%S/Inputs/profsampleacc.extbinary.afdo -profile-summary-cutoff-hot=600000 -profile-sample-accurate -profile-accurate-for-symsinlist -enable-new-pm=0 -S | FileCheck %s --check-prefix=CALL_SUM_IS_WARM
 ; RUN: opt < %s -passes=sample-profile -sample-profile-file=%S/Inputs/profsampleacc.extbinary.afdo -profile-summary-cutoff-hot=900000 -profile-sample-accurate -profile-accurate-for-symsinlist -S | FileCheck %s --check-prefix=CALL_SUM_IS_HOT
 ; RUN: opt < %s -sample-profile -sample-profile-file=%S/Inputs/profsampleacc.extbinary.afdo -profile-summary-cutoff-hot=600000 -profile-sample-accurate -profile-accurate-for-symsinlist -enable-new-pm=0 -S | FileCheck %s --check-prefix=CALL_SUM_IS_WARM
 ; RUN: opt < %s -passes=sample-profile -sample-profile-file=%S/Inputs/profsampleacc.extbinary.afdo -profile-summary-cutoff-hot=900000 -profile-sample-accurate -profile-accurate-for-symsinlist -S | FileCheck %s --check-prefix=CALL_SUM_IS_HOT
 ;
entry:
   store i32 %x, i32* %x.addr, align 4
   store i32 %y, i32* %y.addr, align 4
   %0 = load i32, i32* %x.addr, align 4, !dbg !11
   %1 = load i32, i32* %y.addr, align 4, !dbg !11
   %add = add nsw i32 %0, %1, !dbg !11
   ret i32 %add, !dbg !11
 }
 
+; Check -profile-symbol-list-cut-off=2 will include _Z3toov into profile
+; symbol list and -profile-symbol-list-cut-off=3 will not.
+; PSLCUTOFF2: define i32 @_Z3toov{{.*}}!prof ![[TOO_ID:[0-9]+]]
+; PSLCUTOFF3: define i32 @_Z3toov{{.*}}!prof ![[TOO_ID:[0-9]+]]
+define i32 @_Z3toov(i32 %x, i32 %y) #0 {
+entry:
+  %add = add nsw i32 %x, %y
+  ret i32 %add
+}
+
 ; Function Attrs: uwtable
 define i32 @main() #0 !dbg !7 {
 entry:
   %retval = alloca i32, align 4
   %s = alloca i32, align 4
   %i = alloca i32, align 4
   store i32 0, i32* %retval
   store i32 0, i32* %i, align 4, !dbg !12

 
 !llvm.dbg.cu = !{!0}
 !llvm.module.flags = !{!8, !9}
 !llvm.ident = !{!10}
 
 ; CALL_SUM_IS_HOT: ![[ZERO_ID]] = !{!"function_entry_count", i64 0}
 ; CALL_SUM_IS_WARM: ![[NONZERO_ID]] = !{!"function_entry_count", i64 5179}
 ; PROFSYMLIST: ![[UNKNOWN_ID]] = !{!"function_entry_count", i64 -1}
+; PSLCUTOFF2: ![[TOO_ID]] = !{!"function_entry_count", i64 -1}
+; PSLCUTOFF3: ![[TOO_ID]] = !{!"function_entry_count", i64 0}
 !0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, producer: "clang version 3.5 ", isOptimized: false, emissionKind: NoDebug, file: !1, enums: !2, retainedTypes: !2, globals: !2, imports: !2)
 !1 = !DIFile(filename: "calls.cc", directory: ".")
 !2 = !{}
 !4 = distinct !DISubprogram(name: "sum", line: 3, isLocal: false, isDefinition: true, virtualIndex: 6, flags: DIFlagPrototyped, isOptimized: false, unit: !0, scopeLine: 3, file: !1, scope: !5, type: !6, retainedNodes: !2)
 !5 = !DIFile(filename: "calls.cc", directory: ".")
 !6 = !DISubroutineType(types: !2)
 !7 = distinct !DISubprogram(name: "main", line: 7, isLocal: false, isDefinition: true, virtualIndex: 6, flags: DIFlagPrototyped, isOptimized: false, unit: !0, scopeLine: 7, file: !1, scope: !5, type: !6, retainedNodes: !2)
 !8 = !{i32 2, !"Dwarf Version", i32 4}