[llvm] r242179 - Add support for on-disk hash table lookup with a known hash, for situations where the same key will be looked up in multiple tables.

[David Blaikie]

On Tue, Jul 14, 2015 at 11:40 AM, Richard Smith <richard-llvm at metafoo.co.uk>
wrote:

> Author: rsmith
> Date: Tue Jul 14 13:40:59 2015
> New Revision: 242179
>
> URL: http://llvm.org/viewvc/llvm-project?rev=242179&view=rev
> Log:
> Add support for on-disk hash table lookup with a known hash, for
> situations where the same key will be looked up in multiple tables.
>
> Modified:
>     llvm/trunk/include/llvm/Support/OnDiskHashTable.h
>
> Modified: llvm/trunk/include/llvm/Support/OnDiskHashTable.h
> URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/Support/OnDiskHashTable.h?rev=242179&r1=242178&r2=242179&view=diff
>
> ==============================================================================
> --- llvm/trunk/include/llvm/Support/OnDiskHashTable.h (original)
> +++ llvm/trunk/include/llvm/Support/OnDiskHashTable.h Tue Jul 14 13:40:59
> 2015
> @@ -280,13 +280,19 @@ public:
>    };
>
>    /// \brief Look up the stored data for a particular key.
> -  iterator find(const external_key_type &EKey, Info *InfoPtr = 0) {
> -    if (!InfoPtr)
> -      InfoPtr = &InfoObj;
> -
> -    using namespace llvm::support;
> +  iterator find(const external_key_type &EKey, Info *InfoPtr = nullptr) {
>      const internal_key_type &IKey = InfoObj.GetInternalKey(EKey);
>      hash_value_type KeyHash = InfoObj.ComputeHash(IKey);
> +    return find_hashed(IKey, KeyHash, InfoPtr);
> +  }
> +
> +  /// \brief Look up the stored data for a particular key with a known
> hash.
> +  iterator find_hashed(const internal_key_type &IKey, hash_value_type
> KeyHash,
> +                       Info *InfoPtr = nullptr) {
>

Could/should this be generalized something like DenseMap's find_as instead?

(perhaps with a hash+value tuple convenience/special case) I suppose it
wouldn't make the API any easier for your use case, though - so can
probably wait until someone has a need for such a thing.


> +    using namespace llvm::support;
> +
> +    if (!InfoPtr)
> +      InfoPtr = &InfoObj;
>
>      // Each bucket is just an offset into the hash table file.
>      offset_type Idx = KeyHash & (NumBuckets - 1);
>
>
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