[PATCH] D44547: Remove GnuHashTableSection::getShift2().

[Rui Ueyama via Phabricator via llvm-commits]

ruiu created this revision.
ruiu added a reviewer: grimar.
Herald added subscribers: arichardson, emaste.

Choosing a Shift2 value based on wordsize is cargo-culted from gold.
Assuming that djb hash is a good hash function, choosing bits [4,9]
shouldn't be any worse or better than choosing bits [5,10]. We shouldn't
have copied that behavior that we can't justify in the first place.


https://reviews.llvm.org/D44547

Files:
  lld/ELF/SyntheticSections.cpp
  lld/ELF/SyntheticSections.h
  lld/test/ELF/gnu-hash-table.s


Index: lld/test/ELF/gnu-hash-table.s
===================================================================
--- lld/test/ELF/gnu-hash-table.s
+++ lld/test/ELF/gnu-hash-table.s
@@ -54,7 +54,7 @@
 # EMPTY-NEXT:   Num Buckets: 1
 # EMPTY-NEXT:   First Hashed Symbol Index: 2
 # EMPTY-NEXT:   Num Mask Words: 1
-# EMPTY-NEXT:   Shift Count: 5
+# EMPTY-NEXT:   Shift Count: 6
 # EMPTY-NEXT:   Bloom Filter: [0x0]
 # EMPTY-NEXT:   Buckets: [0]
 # EMPTY-NEXT:   Values: []
@@ -113,8 +113,8 @@
 # I386-NEXT:   Num Buckets: 1
 # I386-NEXT:   First Hashed Symbol Index: 4
 # I386-NEXT:   Num Mask Words: 1
-# I386-NEXT:   Shift Count: 5
-# I386-NEXT:   Bloom Filter: [0x14000220]
+# I386-NEXT:   Shift Count: 6
+# I386-NEXT:   Bloom Filter: [0x4004204]
 # I386-NEXT:   Buckets: [4]
 # I386-NEXT:   Values: [0xB8860BA, 0xB887389]
 # I386-NEXT: }
Index: lld/ELF/SyntheticSections.h
===================================================================
--- lld/ELF/SyntheticSections.h
+++ lld/ELF/SyntheticSections.h
@@ -471,7 +471,7 @@
   void addSymbols(std::vector<SymbolTableEntry> &Symbols);
 
 private:
-  size_t getShift2() const { return Config->Is64 ? 6 : 5; }
+  enum { Shift2 = 6 };
 
   void writeBloomFilter(uint8_t *Buf);
   void writeHashTable(uint8_t *Buf);
Index: lld/ELF/SyntheticSections.cpp
===================================================================
--- lld/ELF/SyntheticSections.cpp
+++ lld/ELF/SyntheticSections.cpp
@@ -1729,7 +1729,7 @@
   write32(Buf, NBuckets);
   write32(Buf + 4, InX::DynSymTab->getNumSymbols() - Symbols.size());
   write32(Buf + 8, MaskWords);
-  write32(Buf + 12, getShift2());
+  write32(Buf + 12, Shift2);
   Buf += 16;
 
   // Write a bloom filter and a hash table.
@@ -1751,7 +1751,7 @@
     size_t I = (Sym.Hash / C) & (MaskWords - 1);
     uint64_t Val = readUint(Buf + I * Config->Wordsize);
     Val |= uint64_t(1) << (Sym.Hash % C);
-    Val |= uint64_t(1) << ((Sym.Hash >> getShift2()) % C);
+    Val |= uint64_t(1) << ((Sym.Hash >> Shift2) % C);
     writeUint(Buf + I * Config->Wordsize, Val);
   }
 }


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