RFR (S): 8164954: split_if creates empty phi and region nodes
nils.eliasson at oracle.com
Mon Mar 6 14:15:14 UTC 2017
The test runtime/Metaspace/FragmentMetaspace.java triggered an assert
(assert(i < _max) failed: oob: i=1, _max=1) when Node::dominates reads
in out of bounds on a empty region node.
The empty region node is created by split_if. Split_if tries to simplify
compares on a constant and a phi, where the phi has at least one
constant on an in edge. In this case the opportunity for optimization is
identified, and a phi and accompanying region node is created for all
remaining in-edges that aren't matching the constant. But here all the
in-edges to the phi matches the constant, and no edge will be split out,
leaving the new nodes without in-edges. Much later in the optimization
phase the empty region node will trigger the assert.
Abort split_if when all in-edges are the same constant - this is already
the desired state. It will be folded later.
A big thank you to Richard Bäckman that helped me track this bug down.
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