[PATCH] D35267: Pass Divergence Analysis data to selection DAG to drive divergence dependent instruction selection

[Alexander via Phabricator via llvm-commits]

alex-t added a comment.

In https://reviews.llvm.org/D35267#946933, @efriedma wrote:

> Does ReplaceAllUsesWith need to propagate changes to the "IsDivergent" bit?


Divergence Analysis is the iterative solver over SSA form. So, after it's done we assume all the Values are correctly annotated with Divergence flag.
When we change some DAG pattern (combiner/legalizer etc) to some other pattern, the Divergence of any new node (and recursively the resulting pattern root) is superposition of the divergence of it's operands.
So we partially repeat the work that was done by the DA but locally - for each newly created node. This work because we assume all the operands have correct bit set.
Any DAG transformation that change divergent pattern to not-divergent or vice versa is illegal.
Given that we don't need to propagate the flag in ReplaceAllUsesWith


https://reviews.llvm.org/D35267