Micro-optimization: don't shift an entire bitcode record over to get the code.

[oota-llvm.git] / lib / Bitcode / Reader / BitstreamReader.cpp

diff --git a/lib/Bitcode/Reader/BitstreamReader.cpp b/lib/Bitcode/Reader/BitstreamReader.cpp
index 9dafe2a036709a383766b0f8f627660b607b3f28..1fd9abd8b1806136f29484810041c4a745af1bda 100644 (file)
--- a/lib/Bitcode/Reader/BitstreamReader.cpp
+++ b/lib/Bitcode/Reader/BitstreamReader.cpp
@@ -204,7 +204,16 @@ unsigned BitstreamCursor::readRecord(unsigned AbbrevID,
 
   const BitCodeAbbrev *Abbv = getAbbrev(AbbrevID);
 
-  for (unsigned i = 0, e = Abbv->getNumOperandInfos(); i != e; ++i) {
+  // Read the record code first.
+  assert(Abbv->getNumOperandInfos() != 0 && "no record code in abbreviation?");
+  const BitCodeAbbrevOp &CodeOp = Abbv->getOperandInfo(0);
+  if (CodeOp.isLiteral())
+    readAbbreviatedLiteral(CodeOp, Vals);
+  else
+    readAbbreviatedField(CodeOp, Vals);
+  unsigned Code = (unsigned)Vals.pop_back_val();
+
+  for (unsigned i = 1, e = Abbv->getNumOperandInfos(); i != e; ++i) {
     const BitCodeAbbrevOp &Op = Abbv->getOperandInfo(i);
     if (Op.isLiteral()) {
       readAbbreviatedLiteral(Op, Vals);
@@ -264,8 +273,6 @@ unsigned BitstreamCursor::readRecord(unsigned AbbrevID,
     JumpToBit(NewEnd);
   }
 
-  unsigned Code = (unsigned)Vals[0];
-  Vals.erase(Vals.begin());
   return Code;
 }