738667 - Experimental: add HALT pseudo-instruction so IR graph always has a single endpoint

Status: RESOLVED WONTFIX

(Tamarin Graveyard :: Optimizing JIT, defect)

Description

[Edwin Smith]

Attachment: WIP to introduce a special halt node

Certian algorithms are simpler if the IR graph always ends at a single node, say HALT.  This node postdominates every other node and is the root of a post-dominator tree.

On the one hand, this simplifies such algorithms.  But on the other hand, its an odd thing to have blocks that logically end, not end -- e.g. return and throw jump to a halt node?

Existing code for doing the postdominator tree works but seems awkward, either this bug should land or the postdominator logic should traverse a CFG with a fake node added to it, even if the fake CFG node doesn't have any IR nodes in it.