From b953e9060e282442d04ae0b8725eaa4d851983db Mon Sep 17 00:00:00 2001
From: Benjamin Kramer <benny.kra@googlemail.com>
Date: Fri, 1 May 2020 15:39:55 +0200
Subject: [PATCH] [Bitcode] reserve in front of push_back loops. NFCI.

---
 llvm/lib/Bitstream/Reader/BitstreamReader.cpp | 18 +++++++-----------
 1 file changed, 7 insertions(+), 11 deletions(-)

diff --git a/llvm/lib/Bitstream/Reader/BitstreamReader.cpp b/llvm/lib/Bitstream/Reader/BitstreamReader.cpp
index 92d7c91..2739137 100644
--- a/llvm/lib/Bitstream/Reader/BitstreamReader.cpp
+++ b/llvm/lib/Bitstream/Reader/BitstreamReader.cpp
@@ -214,6 +214,7 @@ Expected<unsigned> BitstreamCursor::readRecord(unsigned AbbrevID,
     if (!MaybeNumElts)
       return MaybeNumElts.takeError();
     uint32_t NumElts = MaybeNumElts.get();
+    Vals.reserve(Vals.size() + NumElts);
 
     for (unsigned i = 0; i != NumElts; ++i)
       if (Expected<uint64_t> MaybeVal = ReadVBR64(6))
@@ -263,6 +264,7 @@ Expected<unsigned> BitstreamCursor::readRecord(unsigned AbbrevID,
       if (!MaybeNumElts)
         return MaybeNumElts.takeError();
       uint32_t NumElts = MaybeNumElts.get();
+      Vals.reserve(Vals.size() + NumElts);
 
       // Get the element encoding.
       if (i + 2 != e)
@@ -334,8 +336,8 @@ Expected<unsigned> BitstreamCursor::readRecord(unsigned AbbrevID,
       *Blob = StringRef(Ptr, NumElts);
     } else {
       // Otherwise, unpack into Vals with zero extension.
-      for (; NumElts; --NumElts)
-        Vals.push_back((unsigned char)*Ptr++);
+      auto *UPtr = reinterpret_cast<const unsigned char *>(Ptr);
+      Vals.append(UPtr, UPtr + NumElts);
     }
   }
 
@@ -458,21 +460,15 @@ BitstreamCursor::ReadBlockInfoBlock(bool ReadBlockInfoNames) {
         return None;
       if (!ReadBlockInfoNames)
         break; // Ignore name.
-      std::string Name;
-      for (unsigned i = 0, e = Record.size(); i != e; ++i)
-        Name += (char)Record[i];
-      CurBlockInfo->Name = Name;
+      CurBlockInfo->Name = std::string(Record.begin(), Record.end());
       break;
     }
       case bitc::BLOCKINFO_CODE_SETRECORDNAME: {
         if (!CurBlockInfo) return None;
         if (!ReadBlockInfoNames)
           break; // Ignore name.
-        std::string Name;
-        for (unsigned i = 1, e = Record.size(); i != e; ++i)
-          Name += (char)Record[i];
-        CurBlockInfo->RecordNames.push_back(std::make_pair((unsigned)Record[0],
-                                                           Name));
+        CurBlockInfo->RecordNames.emplace_back(
+            (unsigned)Record[0], std::string(Record.begin() + 1, Record.end()));
         break;
       }
       }
-- 
2.7.4