cranelift: Remove redundant dominator-tree structure#7948
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jameysharp merged 4 commits intobytecodealliance:mainfrom Feb 16, 2024
Merged
cranelift: Remove redundant dominator-tree structure#7948jameysharp merged 4 commits intobytecodealliance:mainfrom
jameysharp merged 4 commits intobytecodealliance:mainfrom
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We already know the entry block everywhere we use this.
These two types had nearly identical interfaces except that the latter also supports constant-time dominance checks.
cfallin
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Feb 15, 2024
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Woah, nice find! I had no idea we already had this (which I guess is why we wrote it again).
While I hesitate to violate the law that "any sufficiently advanced compiler contains three domtree implementations" (regalloc2 has one too!), I think we can do some spring cleaning here :-)
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It turns out this was the only thing the egraph pass used the original dominator tree for, so we can stop passing that around. We could also require that the caller of EgraphPass::new construct the DominatorTreePreorder and avoid passing the original tree into the egraph pass at all, but I've chosen to stop refactoring here. We should review all uses of DominatorTree::dominates to see if it makes sense to pass a DominatorTreePreorder around more places.
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LGTM! |
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The egraph work introduced a helper for walking over the dominator tree in pre-order, but it turns out that helper already existed in the
dominator_treemodule itself, and the older version also supports constant-time dominance checks using the same trick that @cfallin suggested in #7891. So let's just use that version.cc: @elliottt @lpereira