[llvm-commits] Patch: avoid reanalyze a node twice in LegalizeTypes

[Duncan Sands]

Hi Mon Ping,

> This patch is to fix an assert that we get for the test case below
>    Assertion failed: (N->getNodeId() !=  
> DAGTypeLegalizer::ReadyToProcess && N->getNodeId() !=
>    DAGTypeLegalizer::Processed && "Invalid node ID for RAUW  
> analysis!"), function ReplaceValue
> 
> In the DAG, we get is something like
> 
> %tmp1 = extract_subvector <2 x double> %tmp0,  <4 x double> %vec, 0
> %tmp2 = extract_element <2 x double> %tmp1, 0
> %tmp3 = extract_element <2 x double> %tmp1, 1
> %tmp4 = build_vector<4 x double> %tmp2, %tmp3, %tmp?, %tmp?
> 
> We discover when examining the operands of %tmp1 that %vec is not a  
> legal type and we split it.  This causes us to replace all uses of  
> %tmp1 which triggers us update %tmp2 and %tmp3 and then update the  
> %tmp4.  The problem is that when we do the update, we will add %tmp4  
> node twice to UpdateListener (NodesToAnalyze) i..e, we add it when we  
> process %tmp2 and again for %tmp3.  When walking through the nodes to  
> reanalyze, the first time we see %tmp4, we update the NodeId to the  
> NewNode.  When we encounter the node again through the list, we hit  
> the assertion since we have already updated that Node.
> 
> The following patch fixes this by changing NodesToAnalyze from  
> SmallVector to use SmallPtrSet to avoid duplicates.  Please let me  
> know of any comments.

thanks for looking into this.  I used SmallVector in order to make
things deterministic - the NodesDeleted set was, as a side-effect,
supposed to avoid duplicates IIRC.  I will try to analyze this later
today.

Ciao,

Duncan.