[llvm-commits] [llvm] r93339 - /llvm/trunk/lib/Bitcode/Writer/BitcodeWriter.cpp

[Devang Patel]

On Wed, Jan 13, 2010 at 1:19 PM, Victor Hernandez <vhernandez at apple.com> wrote:
>
> On Jan 13, 2010, at 1:15 PM, Devang Patel wrote:
>
> On Wed, Jan 13, 2010 at 1:07 PM, Victor Hernandez <vhernandez at apple.com>
> wrote:
>
> On Jan 13, 2010, at 1:05 PM, Devang Patel wrote:
>
> On Wed, Jan 13, 2010 at 11:37 AM, Victor Hernandez <vhernandez at apple.com>
> wrote:
>
>
> +static void WriteFunctionLocalMetadata(const ValueEnumerator &VE,
>
> +                                       BitstreamWriter &Stream) {
>
> +  bool StartedMetadataBlock = false;
>
> +  SmallVector<uint64_t, 64> Record;
>
> +  ValueEnumerator::ValueList Vals = VE.getMDValues();
>
> +  ValueEnumerator::ValueList::iterator it = Vals.begin();
>
> +  ValueEnumerator::ValueList::iterator end = Vals.end();
>
> +
>
> +  while (it != end) {
>
> +    if (const MDNode *N = dyn_cast<MDNode>((*it).first)) {
>
> +      if (N->isFunctionLocal()) {
>
> +        if (!StartedMetadataBlock) {
>
> +          Stream.EnterSubblock(bitc::METADATA_BLOCK_ID, 3);
>
> +          StartedMetadataBlock = true;
>
> +        }
>
> +        WriteMDNode(N, VE, Stream, Record);
>
> +        // Remove function-local MD, since it is used outside of function.
>
> how ?
>
> Sorry that is a typo.  Meant to say "is not used".
>
> but why remove from value list ?
>
> Because the same ValueList (via VE.getMDValues()) is used during all of the
> bitcode-writing.  Function-local metadata needs to exist in the ValueList
> only during the writing of the function it is local to (from its lazy
> enumeration during incorporateFunction until WriteFunctionLocalMetadata() is
> called).  If it does not get removed here, then it will still be
> in VE.getMDValues() when we go to write the next function.
>
>
>
> +        it = Vals.erase(it);
>
> +        end = Vals.end();
>
> +        continue;
>
> +      }
>
> +    }
>
> +    ++it;
>
> +  }
>
> +
>
> +  if (StartedMetadataBlock)
>
> +    Stream.ExitBlock();
>
> +}
>
> +
>
>  static void WriteMetadataAttachment(const Function &F,
>
>                                     const ValueEnumerator &VE,
>
>                                     BitstreamWriter &Stream) {
>
> @@ -1210,6 +1241,7 @@
>
>   // Emit names for all the instructions etc.
>
>   WriteValueSymbolTable(F.getValueSymbolTable(), VE, Stream);
>
> +  WriteFunctionLocalMetadata(VE, Stream);
>
> This does not check function so will it write function local metadata
>
> from one function into another function's block ?
>
> That check is done by the Verifier.  Do you think I need to do it here also?
>
> Are you sure that incoming VE will not have function local metadata
> for another function at this point?
>
> Yes, that is guaranteed by removing function-local metadata as soon as they
> get written.
>

ValueList is not manipulated like this in BitCode Writer. Erasing
element one by one from ValueList may have performance impact.
Instead, it is better to keep ValueList intact and check function in
WriteFunctionLocalMetadata() and update isFunctionLocal() to return
Function *.

-
Devang