[BOLT] Fix merge-fdata handling of BAT profiles

[rafauler]

Summary

When a profile is collected in a BOLTed binary, the generated
profile is tagged with a header string "boltedcollection" in the first
line of the fdata file. Fix merge-fdata to recognize this header
string and preserve it into the output.

[rafauler]

Fixed some typos

[Amir]

LGTM

bolt/test/X86/Inputs/bat_profile_1.fdata

+boltedcollection
+1 main 451 1 SolveCubic 0 0 151
+1 main 489 1 main 46a 0 27
+1 main 4ad 1 main 428 0 135
+1 main 4cb 1 main 410 2 19
+1 main 4e9 1 main 3fa 0 1
+1 main 521 1 usqrt 0 0 168
+1 main 543 1 main 519 0 179
+1 main 55c 1 usqrt 0 0 31
+1 main 57f 1 main 554 0 34
+1 main 5d6 1 main 58f 0 1001
+1 main 62d 1 main 5e6 0 22
+1 SolveCubic 82 1 SolveCubic 130 2 4
+1 SolveCubic 107 1 SolveCubic 111 0 89
+1 SolveCubic 12c 1 main 456 0 87
+1 SolveCubic 2a6 1 main 456 0 5
+1 usqrt 30 1 usqrt 39 171 2886
+1 usqrt 3d 1 usqrt 10 33 4711
+1 usqrt 42 1 main 526 0 73
+1 usqrt 42 1 main 561 0 19

bolt/test/X86/Inputs/bat_profile_2.fdata

+boltedcollection
+1 main 451 1 SolveCubic 0 0 151
+1 main 489 1 main 46a 0 27
+1 main 4ad 1 main 428 0 135
+1 main 4cb 1 main 410 2 19
+1 main 4e9 1 main 3fa 0 1
+1 main 521 1 usqrt 0 0 168
+1 main 543 1 main 519 0 179
+1 main 55c 1 usqrt 0 0 31
+1 main 57f 1 main 554 0 34
+1 main 5d6 1 main 58f 0 1001
+1 main 62d 1 main 5e6 0 22
+1 SolveCubic 82 1 SolveCubic 130 2 4
+1 SolveCubic 107 1 SolveCubic 111 0 89
+1 SolveCubic 12c 1 main 456 0 87
+1 SolveCubic 2a6 1 main 456 0 5
+1 usqrt 30 1 usqrt 39 171 2886
+1 usqrt 3d 1 usqrt 10 33 4711
+1 usqrt 42 1 main 526 0 73
+1 usqrt 42 1 main 561 0 19

bolt/test/X86/merge-fdata-bat-mode.test

+# Check merge-fdata tool correctly processes fdata files with header strings
+# such as the ones produced by BAT mode (bolted_collection)
+RUN: merge-fdata %S/Inputs/bat_profile_1.fdata \
+RUN:             %S/Inputs/bat_profile_2.fdata 2> %t.error \
+RUN:   | FileCheck %s --check-prefix=CHECK-FDATA
+RUN: cat %t.error |& FileCheck %s --check-prefix=CHECK-ERROR
+
+CHECK-ERROR-NOT:  malformed
+
+CHECK-FDATA: 1 main 451 1 SolveCubic 0 0 302
+
+

bolt/tools/merge-fdata/merge-fdata.cpp

for (const std::string &Filename : Filenames) {
     StringRef Buf = MB.get()->getBuffer();
     // Check if the string "boltedcollection" is in the first line
     if (Buf.startswith("boltedcollection\n")) {
       if (!First && !BoltedCollection)
         report_error(
             Filename,
             "cannot mix profile collected in BOLT and non-BOLT deployments");
       BoltedCollection = true;
-      if (!First)
-        Buf = Buf.drop_front(17);
     } else {
       if (BoltedCollection)
         report_error(
             Filename,
             "cannot mix profile collected in BOLT and non-BOLT deployments");
     }
 
     SmallVector<StringRef, 10> Lines;
     SplitString(Buf, Lines, "\n");
     for (StringRef Line : Lines) {
       size_t Pos = Line.rfind(" ");
       if (Pos == StringRef::npos)
         report_error(Filename, "Malformed / corrupted profile");
       StringRef Signature = Line.substr(0, Pos);
       uint64_t Count;
       if (Line.substr(Pos + 1, Line.size() - Pos).getAsInteger(10, Count))
         report_error(Filename, "Malformed / corrupted profile counter");
       Count += Entries.lookup(Signature);
       Entries.insert_or_assign(Signature, Count);
     }
     First = false;
   }
 
+  if (BoltedCollection)
+    outs() << "boltedcollection\n";
   for (const auto &Entry : Entries)
     outs() << Entry.getKey() << " " << Entry.getValue() << "\n";
 
   errs() << "Profile from " << Filenames.size() << " files merged.\n";
 }
 
 } // anonymous namespace