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LLVM needs a generic update SSA mechanism #589

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lattner opened this issue Feb 1, 2004 · 13 comments
Closed

LLVM needs a generic update SSA mechanism #589

lattner opened this issue Feb 1, 2004 · 13 comments

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@lattner
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lattner commented Feb 1, 2004

Bugzilla Link 217
Resolution FIXED
Resolved on Oct 10, 2009 21:09
Version trunk
OS All
CC @asl,@lattner,@nlewycky

Extended Description

Certain transformations, like tail-duplication (Bug 174) and the correlated
expression elimination pass, fundamentally need to make arbitrary changes to the
CFG AND update the SSA form of expressions. To do this, they need to update
dominators and dominator frontiers as they change the CFG.

Basically the dominator information passes need an 'addEdge/removeEdge'
interface that clients can use to incrementally update the dominator
information. There is a paper that describes how to do this:

http://citeseer.nj.nec.com/sreedhar94efficient.html

... someone should implement it.

Given this functionality, many other transformations would also be able to
incrementally update dominator information, instead of recalculating it, which
would speed up the optimizer as well.

-Chris
@lattner
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lattner commented Feb 26, 2004

Changing all of these bugs who do not have people looking at them to be assigned
to "unassignedbugs", indicating that if someone is feeling ambitious, they can
take ownership of the bug.

If I stole your bug, and you still want it, feel free to take ownership back.

-Chris

3 similar comments
@lattner
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lattner commented Feb 26, 2004

Changing all of these bugs who do not have people looking at them to be assigned
to "unassignedbugs", indicating that if someone is feeling ambitious, they can
take ownership of the bug.

If I stole your bug, and you still want it, feel free to take ownership back.

-Chris

@lattner
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lattner commented Feb 26, 2004

Changing all of these bugs who do not have people looking at them to be assigned
to "unassignedbugs", indicating that if someone is feeling ambitious, they can
take ownership of the bug.

If I stole your bug, and you still want it, feel free to take ownership back.

-Chris

@lattner
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lattner commented Feb 26, 2004

Changing all of these bugs who do not have people looking at them to be assigned
to "unassignedbugs", indicating that if someone is feeling ambitious, they can
take ownership of the bug.

If I stole your bug, and you still want it, feel free to take ownership back.

-Chris

@nlewycky
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I would also like this for my pass in llvm/llvm-bugzilla-archive#807 .

Unfortunately, my compiler theory is no match for this paper. What does it mean
on page 14:
"2. PseudoAffected: This set consists of any /proper/ descendant of a
PossiblyAffected node." Assuming that I have the list of PossiblyAffected
nodes, what are the proper descendants? Every node in the sub-tree?

@nlewycky
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it compiles, but i've never run it.
I tried to implement it and this is as far as I got.

@llvmbot
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llvmbot commented Apr 11, 2007

Nick,

If you're still interested in this, there's an expanded/clearer version of the
paper at:

http://citeseer.ist.psu.edu/sreedhar95incremental.html

Otherwise, I might tackle this next time I need something to do.

--Owen

@lattner
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lattner commented Apr 15, 2007

Step #​1 complete: Owen removed idom.

@lattner
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lattner commented Oct 10, 2009

Implemented here:
http://lists.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20091005/088600.html

Jump threading switched to use it here:
http://lists.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20091005/088601.html

@llvmbot
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llvmbot commented Oct 11, 2009

Chris, I don't think that solves all of what this bug asks for. We're still lacking a generc dominato r update function.

@lattner
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lattner commented Oct 11, 2009

As originator of the bug, I know what it was about. :) Updating domtree wasn't the point, that was seen as a way to get to SSA updates.

@llvmbot
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llvmbot commented Oct 11, 2009

Would it be worthwhile to split dominator updates into a new PR? It still seems like a useful feature.

@lattner
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lattner commented Oct 11, 2009

Why? If it existed, we still wouldn't use it in the standard optimizer (too slow). Lets wait until there is an actual reason to have it.

@llvmbot llvmbot transferred this issue from llvm/llvm-bugzilla-archive Dec 1, 2021
This issue was closed.
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@nlewycky @lattner @llvmbot