[PATCH] D135125: [JumpThreading] Reverse the order of basic block iteration.
Usman Nadeem via Phabricator via llvm-commits
llvm-commits at lists.llvm.org
Thu Oct 6 11:38:26 PDT 2022
mnadeem added a comment.
In D135125#3840548 <https://reviews.llvm.org/D135125#3840548>, @efriedma wrote:
>> When JT is called on ._crit_edge2292, %uglygep.13072 is replicated in the threaded block and a PHI node (lets say %phi.1) is inserted into the successor i.e. ._crit_edge2292.1. In the next iteration JT is called on ._crit_edge2292.1 and we now need to build two PHI nodes when rewriting the SSA. One for the new value %uglygep.23073 and one for %phi.1 that we created earlier. The number of new phi nodes we need to build keeps adding up as we go down the chain.
>
> I'm not sure I understand the growth aspect here; %uglygep.13072 isn't defined or used in any of the blocks that are getting replicated? Or is the issue that the SSA algorithm spends time trying to rewrite things that don't need to be rewritten? Would using SSAUpdaterBulk in JumpThreadingPass::updateSSA help?
The SSA algorithm spends time trying to rewrite things that actually need to be rewritten but we have *more of these things* compared to when we do bottom up threading. I will try to see if SSAUpdaterBulk helps.
I am not sure if I am doing a good job of explaining it, try running `opt -jump-threading -debug-only=jump-threading` on this test file and you will quickly see what the issue is from the debug dump.
Full .ll file : https://gist.github.com/UsmanNadeem/bfa78d0390d103275792afdd21069d2c
`%uglygep.13072` is defined in `._crit_edge2292` and used in `.lr.ph2291.1 and .lr.ph2669.1`. `._crit_edge2292` gets replicated and a phi node put in its successor `._crit_edge2292.1`.
Next time `._crit_edge2292.1` gets replicated with 1 phi node and one gep, after one more iteration `._crit_edge2292.2` gets replicated with 2 phi nodes and one gep, this goes on until we reach `._crit_edge2292.24` when we have 24 phi nodes that need to be replicated.
Threading edge from '._crit_edge2292.23.thread' to '._crit_edge2292.25, across block:
._crit_edge2292.24: ; preds = %._crit_edge2292.23.thread, %.lr.ph2291.24
%uglygep.243095600 = phi ptr [ %uglygep.243095576, %._crit_edge2292.23.thread ], [ %uglygep.243095, %.lr.ph2291.24 ]
%uglygep.223093506530599 = phi ptr [ %uglygep.223093484, %._crit_edge2292.23.thread ], [ %uglygep.223093, %.lr.ph2291.24 ]
%uglygep.203091420442505531598 = phi ptr [ %uglygep.203091400, %._crit_edge2292.23.thread ], [ %uglygep.203091, %.lr.ph2291.24 ]
%uglygep.183089342362419443504532597 = phi ptr [ %uglygep.183089324, %._crit_edge2292.23.thread ], [ %uglygep.183089, %.lr.ph2291.24 ]
%uglygep.163087272290341363418444503533596 = phi ptr [ %uglygep.163087256, %._crit_edge2292.23.thread ], [ %uglygep.163087, %.lr.ph2291.24 ]
%uglygep.143085210226271291340364417445502534595 = phi ptr [ %uglygep.143085196, %._crit_edge2292.23.thread ], [ %uglygep.143085, %.lr.ph2291.24 ]
%uglygep.123083156170209227270292339365416446501535594 = phi ptr [ %uglygep.123083144, %._crit_edge2292.23.thread ], [ %uglygep.123083, %.lr.ph2291.24 ]
%uglygep.103081110122155171208228269293338366415447500536593 = phi ptr [ %uglygep.103081100, %._crit_edge2292.23.thread ], [ %uglygep.103081, %.lr.ph2291.24 ]
%uglygep.830797282109123154172207229268294337367414448499537592 = phi ptr [ %uglygep.8307964, %._crit_edge2292.23.thread ], [ %uglygep.83079, %.lr.ph2291.24 ]
%uglygep.6307742507183108124153173206230267295336368413449498538591 = phi ptr [ %uglygep.6307736, %._crit_edge2292.23.thread ], [ %uglygep.63077, %.lr.ph2291.24 ]
%uglygep.43075202641517084107125152174205231266296335369412450497539590 = phi ptr [ %uglygep.4307516, %._crit_edge2292.23.thread ], [ %uglygep.43075, %.lr.ph2291.24 ]
%uglygep.23073610192740526985106126151175204232265297334370411451496540589 = phi ptr [ %uglygep.230734, %._crit_edge2292.23.thread ], [ %uglygep.23073, %.lr.ph2291.24 ]
%uglygep.130722511182839536886105127150176203233264298333371410452495541588 = phi ptr [ %uglygep.130721, %._crit_edge2292.23.thread ], [ %uglygep.13072, %.lr.ph2291.24 ]
%uglygep.3307412172938546787104128149177202234263299332372409453494542587 = phi ptr [ %uglygep.330749, %._crit_edge2292.23.thread ], [ %uglygep.33074, %.lr.ph2291.24 ]
%uglygep.530763037556688103129148178201235262300331373408454493543586 = phi ptr [ %uglygep.5307625, %._crit_edge2292.23.thread ], [ %uglygep.53076, %.lr.ph2291.24 ]
%uglygep.73078566589102130147179200236261301330374407455492544585 = phi ptr [ %uglygep.7307849, %._crit_edge2292.23.thread ], [ %uglygep.73078, %.lr.ph2291.24 ]
%uglygep.9308090101131146180199237260302329375406456491545584 = phi ptr [ %uglygep.9308081, %._crit_edge2292.23.thread ], [ %uglygep.93080, %.lr.ph2291.24 ]
%uglygep.113082132145181198238259303328376405457490546583 = phi ptr [ %uglygep.113082121, %._crit_edge2292.23.thread ], [ %uglygep.113082, %.lr.ph2291.24 ]
%uglygep.133084182197239258304327377404458489547582 = phi ptr [ %uglygep.133084169, %._crit_edge2292.23.thread ], [ %uglygep.133084, %.lr.ph2291.24 ]
%uglygep.153086240257305326378403459488548581 = phi ptr [ %uglygep.153086225, %._crit_edge2292.23.thread ], [ %uglygep.153086, %.lr.ph2291.24 ]
%uglygep.173088306325379402460487549580 = phi ptr [ %uglygep.173088289, %._crit_edge2292.23.thread ], [ %uglygep.173088, %.lr.ph2291.24 ]
%uglygep.193090380401461486550579 = phi ptr [ %uglygep.193090361, %._crit_edge2292.23.thread ], [ %uglygep.193090, %.lr.ph2291.24 ]
%uglygep.213092462485551578 = phi ptr [ %uglygep.213092441, %._crit_edge2292.23.thread ], [ %uglygep.213092, %.lr.ph2291.24 ]
%uglygep.233094552577 = phi ptr [ %uglygep.233094529, %._crit_edge2292.23.thread ], [ %uglygep.233094, %.lr.ph2291.24 ]
%uglygep.253096 = getelementptr i8, ptr %40, i64 800, !dbg !127
br i1 %.not2713, label %._crit_edge2292.25, label %.lr.ph2291.25, !dbg !127
JT: Renaming non-local uses of: %uglygep.243095600 = phi ptr [ %uglygep.243095, %.lr.ph2291.24 ]
JT: Renaming non-local uses of: %uglygep.223093506530599 = phi ptr [ %uglygep.223093, %.lr.ph2291.24 ]
JT: Renaming non-local uses of: %uglygep.203091420442505531598 = phi ptr [ %uglygep.203091, %.lr.ph2291.24 ]
JT: Renaming non-local uses of: %uglygep.183089342362419443504532597 = phi ptr [ %uglygep.183089, %.lr.ph2291.24 ]
JT: Renaming non-local uses of: %uglygep.163087272290341363418444503533596 = phi ptr [ %uglygep.163087, %.lr.ph2291.24 ]
JT: Renaming non-local uses of: %uglygep.143085210226271291340364417445502534595 = phi ptr [ %uglygep.143085, %.lr.ph2291.24 ]
JT: Renaming non-local uses of: %uglygep.123083156170209227270292339365416446501535594 = phi ptr [ %uglygep.123083, %.lr.ph2291.24 ]
JT: Renaming non-local uses of: %uglygep.103081110122155171208228269293338366415447500536593 = phi ptr [ %uglygep.103081, %.lr.ph2291.24 ]
JT: Renaming non-local uses of: %uglygep.830797282109123154172207229268294337367414448499537592 = phi ptr [ %uglygep.83079, %.lr.ph2291.24 ]
JT: Renaming non-local uses of: %uglygep.6307742507183108124153173206230267295336368413449498538591 = phi ptr [ %uglygep.63077, %.lr.ph2291.24 ]
JT: Renaming non-local uses of: %uglygep.43075202641517084107125152174205231266296335369412450497539590 = phi ptr [ %uglygep.43075, %.lr.ph2291.24 ]
JT: Renaming non-local uses of: %uglygep.23073610192740526985106126151175204232265297334370411451496540589 = phi ptr [ %uglygep.23073, %.lr.ph2291.24 ]
JT: Renaming non-local uses of: %uglygep.130722511182839536886105127150176203233264298333371410452495541588 = phi ptr [ %uglygep.13072, %.lr.ph2291.24 ]
JT: Renaming non-local uses of: %uglygep.3307412172938546787104128149177202234263299332372409453494542587 = phi ptr [ %uglygep.33074, %.lr.ph2291.24 ]
JT: Renaming non-local uses of: %uglygep.530763037556688103129148178201235262300331373408454493543586 = phi ptr [ %uglygep.53076, %.lr.ph2291.24 ]
JT: Renaming non-local uses of: %uglygep.73078566589102130147179200236261301330374407455492544585 = phi ptr [ %uglygep.73078, %.lr.ph2291.24 ]
JT: Renaming non-local uses of: %uglygep.9308090101131146180199237260302329375406456491545584 = phi ptr [ %uglygep.93080, %.lr.ph2291.24 ]
JT: Renaming non-local uses of: %uglygep.113082132145181198238259303328376405457490546583 = phi ptr [ %uglygep.113082, %.lr.ph2291.24 ]
JT: Renaming non-local uses of: %uglygep.133084182197239258304327377404458489547582 = phi ptr [ %uglygep.133084, %.lr.ph2291.24 ]
JT: Renaming non-local uses of: %uglygep.153086240257305326378403459488548581 = phi ptr [ %uglygep.153086, %.lr.ph2291.24 ]
JT: Renaming non-local uses of: %uglygep.173088306325379402460487549580 = phi ptr [ %uglygep.173088, %.lr.ph2291.24 ]
JT: Renaming non-local uses of: %uglygep.193090380401461486550579 = phi ptr [ %uglygep.193090, %.lr.ph2291.24 ]
JT: Renaming non-local uses of: %uglygep.213092462485551578 = phi ptr [ %uglygep.213092, %.lr.ph2291.24 ]
JT: Renaming non-local uses of: %uglygep.233094552577 = phi ptr [ %uglygep.233094, %.lr.ph2291.24 ]
JT: Renaming non-local uses of: %uglygep.253096 = getelementptr i8, ptr %40, i64 800, !dbg !127
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D135125/new/
https://reviews.llvm.org/D135125
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