Compute the DISubprogram hash key partially (NFC)

[mehdi_amini]

Summary

This patch changes the computation of the hash key for DISubprogram to
be computed on a small subset of the fields. The hash is computed a
lot faster, but there might be more collision in the table.
However by carefully selecting the fields, colisions should be rare.

Using opt to load the IR for FastISelEmitter.cpp.o, with this patch:

• DISubprogram::getImpl() goes from 28ms to 15ms.
• DICompositeType::getImpl() goes from 6ms to 2ms
• DIDerivedType::getImpl() goes from 18 to 12ms

[mehdi_amini]

Applies to other metadata types

[echristo]

I'll let Duncan review this more, but as a quick side note - would you mind
making the ordering of arguments a little more regular? Name, File, Line,
Scope or something?

-eric

[mehdi_amini]

Change the order of arguments as suggested by Eric.

Duncan?

[dexonsmith]

Sorry, I thought I'd responded back in January. This approach SGTM.

I have some ideas about field choice below. If you've profiled -flto -g
with something non-trivial, then I'm happy for you to commit (LGTM!), but
you might be able to extract even better performance.

[mehdi_amini]

Update field list: checked an LTO build of llvm-tblgen and made sure there are (almost) no collisions.

[mehdi_amini]

(mark as accepted before closing)

[mehdi_amini]

r263866

lib/IR/LLVMContextImpl.h

return Tag == RHS->getTag() && Name == RHS->getRawName() &&
            File == RHS->getRawFile() && Line == RHS->getLine() &&
            Scope == RHS->getRawScope() && BaseType == RHS->getRawBaseType() &&
            SizeInBits == RHS->getSizeInBits() &&
            AlignInBits == RHS->getAlignInBits() &&
            OffsetInBits == RHS->getOffsetInBits() && Flags == RHS->getFlags() &&
            ExtraData == RHS->getRawExtraData();
   }
   unsigned getHashValue() const {
-    return hash_combine(Tag, Name, File, Line, Scope, BaseType, SizeInBits,
-                        AlignInBits, OffsetInBits, Flags, ExtraData);
+    return hash_combine(Name, File, Line, Scope, BaseType);
   }
 };
 
 template <> struct MDNodeKeyImpl<DICompositeType> {
   unsigned Tag;
   MDString *Name;
   Metadata *File;
   unsigned Line;
return Tag == RHS->getTag() && Name == RHS->getRawName() &&
            OffsetInBits == RHS->getOffsetInBits() && Flags == RHS->getFlags() &&
            Elements == RHS->getRawElements() &&
            RuntimeLang == RHS->getRuntimeLang() &&
            VTableHolder == RHS->getRawVTableHolder() &&
            TemplateParams == RHS->getRawTemplateParams() &&
            Identifier == RHS->getRawIdentifier();
   }
   unsigned getHashValue() const {
-    return hash_combine(Tag, Name, File, Line, Scope, BaseType, SizeInBits,
-                        AlignInBits, OffsetInBits, Flags, Elements, RuntimeLang,
-                        VTableHolder, TemplateParams, Identifier);
+    return hash_combine(Name, File, Line, Scope, SizeInBits, Elements);
   }
 };
 
 template <> struct MDNodeKeyImpl<DISubroutineType> {
   unsigned Flags;
   Metadata *TypeArray;
 
   MDNodeKeyImpl(int64_t Flags, Metadata *TypeArray)
return Scope == RHS->getRawScope() && Name == RHS->getRawName() &&
            Virtuality == RHS->getVirtuality() &&
            VirtualIndex == RHS->getVirtualIndex() && Flags == RHS->getFlags() &&
            IsOptimized == RHS->isOptimized() &&
            TemplateParams == RHS->getRawTemplateParams() &&
            Declaration == RHS->getRawDeclaration() &&
            Variables == RHS->getRawVariables();
   }
   unsigned getHashValue() const {
-    return hash_combine(Scope, Name, LinkageName, File, Line, Type,
-                        IsLocalToUnit, IsDefinition, ScopeLine, ContainingType,
-                        Virtuality, VirtualIndex, Flags, IsOptimized,
-                        TemplateParams, Declaration, Variables);
+    return hash_combine(Scope, File, Type, Line);
   }
 };
 
 template <> struct MDNodeKeyImpl<DILexicalBlock> {
   Metadata *Scope;
   Metadata *File;
   unsigned Line;
   unsigned Column;