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cmd/compile: compilation of a package >100x slower with 1.20rc3 #57959

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aarzilli opened this issue Jan 23, 2023 · 15 comments
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cmd/compile: compilation of a package >100x slower with 1.20rc3 #57959

aarzilli opened this issue Jan 23, 2023 · 15 comments
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compiler/runtime Issues related to the Go compiler and/or runtime. NeedsFix The path to resolution is known, but the work has not been done. Performance release-blocker
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@aarzilli
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aarzilli commented Jan 23, 2023

The package in question is https://github.com/benoitkugler/textlayout/fonts/glyphsnames in v0.3.0, with go 1.19:

$ go version
go version go1.19.1 linux/amd64
$ time go build

real	0m4,086s
user	0m5,970s
sys	0m0,447s

with go 1.20rc3 I got bored of waiting after 10 minutes, so it's at least 100x slower, but possibly a lot more (for all I know it could be in an infinite loop).

The code in question seems to have some very large (and very questionable) switch statements.

@gopherbot gopherbot added the compiler/runtime Issues related to the Go compiler and/or runtime. label Jan 23, 2023
@seankhliao
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there's a 12000 line / 6000 case switch in there

@seankhliao seankhliao added Performance NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. labels Jan 23, 2023
@seankhliao
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main » time go1.19.5 build -a               
go1.19.5 build -a  9.57s user 0.79s system 279% cpu 3.702 total

main » gotip version         
go version devel go1.21-e2fe35363d0 Mon Jan 23 10:02:20 2023 +0000 linux/amd64

main » time gotip build -a
gotip build -a  3983.07s user 58.04s system 771% cpu 8:43.65 total

@randall77
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@randall77
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Nope. Looks like the compiler is stuck/slow in prove. I think it is https://go-review.googlesource.com/c/go/+/410336
@wdvxdr1123 @cuonglm

@randall77
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Looks like all the OR operations are added for string equality - we do things like load 4 bytes, build a 32-bit value using shifts and ORs, then do a comparison with a 32-bit constant.
(The loads get combined into a single 32-bit load, but not until after the prove pass.)

@heschi
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heschi commented Jan 23, 2023

Marking as a tentative release blocker.

@randall77
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Reverting CL 410336 is probably the simplest way forward. I'll do that tomorrow if no better ideas surface today.

@wdvxdr1123
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I agree about reverting CL 410336.

@cuonglm
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cuonglm commented Jan 24, 2023

@randall77 could we use v.AuxInt to indicate that prove should ignore the value instead of updating to fact table?

@randall77
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@cuonglm Maybe, but I'd rather not. There's then this weird semantic-free mark that we'd have to ensure makes it to the prove pass. Can we CSE an OR with and without the mark? Do all rewrite rules have to propagate that mark? e.g.

(Or64 (Const64 <t> [c]) (Or64 (Const64 <t> [d]) x)) => (Or64 (Const64 <t> [c|d]) x)

If anything, maybe we could figure out when we don't need to prove anything about a value during the prove pass itself. Maybe if the result of an OR is only used in subsequent ORs and shifts, then don't record anything about it. Or something like that.

Or just make prove good enough to handle recording lots of facts without a big slowdown.

@gopherbot
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Change https://go.dev/cl/463295 mentions this issue: Revert "cmd/compile: teach prove about bitwise OR operation"

gopherbot pushed a commit that referenced this issue Jan 24, 2023
This reverts commit 3680b5e.

Reason for revert: causes long compile times on certain functions. See issue #57959

Change-Id: Ie9e881ca8abbc79a46de2bfeaed0b9d6c416ed42
Reviewed-on: https://go-review.googlesource.com/c/go/+/463295
Run-TryBot: Keith Randall <khr@golang.org>
Reviewed-by: David Chase <drchase@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>
@randall77
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This is fixed at tip. Milestoning for 1.20 for the backport.

@randall77 randall77 added this to the Go1.20 milestone Jan 24, 2023
@dmitshur dmitshur added NeedsFix The path to resolution is known, but the work has not been done. and removed NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. labels Jan 24, 2023
@gopherbot
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Change https://go.dev/cl/463415 mentions this issue: [release-branch.go1.20] Revert "cmd/compile: teach prove about bitwise OR operation"

gopherbot pushed a commit that referenced this issue Jan 25, 2023
…e OR operation"

This reverts commit 3680b5e.

Reason for revert: causes long compile times on certain functions. See issue #57959

Change-Id: Ie9e881ca8abbc79a46de2bfeaed0b9d6c416ed42
Reviewed-on: https://go-review.googlesource.com/c/go/+/463295
Run-TryBot: Keith Randall <khr@golang.org>
Reviewed-by: David Chase <drchase@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>
(cherry picked from commit a6ddb15)
Reviewed-on: https://go-review.googlesource.com/c/go/+/463415
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Keith Randall <khr@golang.org>
Auto-Submit: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Keith Randall <khr@google.com>
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Closed by merging 10124c2 to release-branch.go1.20.

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