Optimize the loading of an identifier from a PCH file when given the
identifier's ID. In this case, we know where the identifier's entry is
located in the hash table (it starts right before the identifier
string itself), so skip the hash table lookup and read the entry
directly. The performance improvement here is, gain, hard to quantify,
but it's the right thing to do.
git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@70078 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Frontend/PCHReader.cpp b/lib/Frontend/PCHReader.cpp
index 6f1ff32..40e5c0d 100644
--- a/lib/Frontend/PCHReader.cpp
+++ b/lib/Frontend/PCHReader.cpp
@@ -2842,6 +2842,7 @@
if (!IdentifiersLoaded[ID - 1]) {
uint32_t Offset = IdentifierOffsets[ID - 1];
+ const char *Str = IdentifierTableData + Offset;
// If there is an identifier lookup table, but the offset of this
// string is after the identifier table itself, then we know that
@@ -2850,23 +2851,40 @@
// identifier.
PCHIdentifierLookupTable *IdTable
= (PCHIdentifierLookupTable *)IdentifierLookupTable;
- bool SkipHashTable = IdTable &&
- Offset >= uint32_t(IdTable->getBuckets() - IdTable->getBase());
+ if (!IdTable ||
+ Offset >= uint32_t(IdTable->getBuckets() - IdTable->getBase())) {
+ // Turn off lookup into the on-disk hash table. We know that
+ // this identifier is not there.
+ if (IdTable)
+ PP.getIdentifierTable().setExternalIdentifierLookup(0);
- if (SkipHashTable)
- PP.getIdentifierTable().setExternalIdentifierLookup(0);
+ // All of the strings in the PCH file are preceded by a 16-bit
+ // length. Extract that 16-bit length to avoid having to execute
+ // strlen().
+ const char *StrLenPtr = Str - 2;
+ unsigned StrLen = (((unsigned) StrLenPtr[0])
+ | (((unsigned) StrLenPtr[1]) << 8)) - 1;
+ IdentifiersLoaded[ID - 1] = &Context.Idents.get(Str, Str + StrLen);
- // All of the strings in the PCH file are preceded by a 16-bit
- // length. Extract that 16-bit length to avoid having to run
- // strlen().
- const char *Str = IdentifierTableData + Offset;
- const char *StrLenPtr = Str - 2;
- unsigned StrLen = (((unsigned) StrLenPtr[0])
- | (((unsigned) StrLenPtr[1]) << 8)) - 1;
- IdentifiersLoaded[ID - 1] = &Context.Idents.get(Str, Str + StrLen);
+ // Turn on lookup into the on-disk hash table, if we have an
+ // on-disk hash table.
+ if (IdTable)
+ PP.getIdentifierTable().setExternalIdentifierLookup(this);
+ } else {
+ // The identifier is a key in our on-disk hash table. Since we
+ // know where the hash table entry starts, just read in this
+ // (key, value) pair.
+ PCHIdentifierLookupTrait Trait(const_cast<PCHReader &>(*this));
+ const unsigned char *Pos = (const unsigned char *)Str - 4;
+ std::pair<unsigned, unsigned> KeyDataLengths
+ = Trait.ReadKeyDataLength(Pos);
- if (SkipHashTable)
- PP.getIdentifierTable().setExternalIdentifierLookup(this);
+ PCHIdentifierLookupTrait::internal_key_type InternalKey
+ = Trait.ReadKey(Pos, KeyDataLengths.first);
+ Pos = (const unsigned char *)Str + KeyDataLengths.first;
+ IdentifiersLoaded[ID - 1] = Trait.ReadData(InternalKey, Pos,
+ KeyDataLengths.second);
+ }
}
return IdentifiersLoaded[ID - 1];