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cmd/compile/internal/ssa: more location lists could be merged #65005

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ajwerner opened this issue Jan 8, 2024 · 2 comments · May be fixed by #65006
Open

cmd/compile/internal/ssa: more location lists could be merged #65005

ajwerner opened this issue Jan 8, 2024 · 2 comments · May be fixed by #65006
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binary-size compiler/runtime Issues related to the Go compiler and/or runtime. NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one.
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Backlog

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@ajwerner
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ajwerner commented Jan 8, 2024 •
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Go version

go version go1.21.5 linux/amd64

`go env` output 
GO111MODULE=''
GOARCH='amd64'
GOBIN=''
GOCACHE='/home/ajwerner/.cache/go-build'
GOENV='/home/ajwerner/.config/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFLAGS=''
GOHOSTARCH='amd64'
GOHOSTOS='linux'
GOINSECURE=''
GOMODCACHE='/home/ajwerner/go/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='linux'
GOPATH='/home/ajwerner/go'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/home/ajwerner/sdk/go1.21.5'
GOSUMDB='sum.golang.org'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/home/ajwerner/sdk/go1.21.5/pkg/tool/linux_amd64'
GOVCS=''
GOVERSION='go1.21.5'
GCCGO='gccgo'
GOAMD64='v1'
AR='ar'
CC='gcc'
CXX='g++'
CGO_ENABLED='1'
GOMOD='/dev/null'
GOWORK=''
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
PKG_CONFIG='pkg-config'
GOGCCFLAGS='-fPIC -m64 -pthread -Wl,--no-gc-sections -fmessage-length=0 -ffile-prefix-map=/tmp/go-build2531477809=/tmp/go-build -gno-record-gcc-switches'

What did you do?

I compiled so go programs and looked at their location lists. I have a fix for this but wanted to create an issue to reference and track it.

What did you see happen?

Sometimes I'd see location lists with adjacent PC ranges and the same locations for variables.

What did you expect to see?

I expected to see these location lists merged.
@gopherbot gopherbot added the compiler/runtime Issues related to the Go compiler and/or runtime. label Jan 8, 2024
ajwerner added a commit to ajwerner/go that referenced this issue Jan 8, 2024
@ajwerner
cmd/compile/internal/ssa: merge more loc lists
4b1a278 
Before this change, the logic to merge location lists would choose not
to merge if the old and new entries were both on the stack, but the new
entry was in fewer registers than old one or if both locations were in
registers but the new one is no longer in a register that was not going
to be output.

Fixes golang#65005
@ajwerner ajwerner linked a pull request Jan 8, 2024 that will close this issue
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@gopherbot
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Change https://go.dev/cl/554515 mentions this issue: cmd/compile/internal/ssa: merge more loc lists

@ajwerner
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ajwerner commented Jan 8, 2024

This bug has a substantial impact on the size of location lists. For example, for cockroach this change reduces the size of the .debug_loc section by 848164 bytes or 7.1%.

ajwerner added a commit to ajwerner/go that referenced this issue Jan 8, 2024
@ajwerner
cmd/compile/internal/ssa: merge more loc lists
52390a6 
Before this change, the logic to merge location lists would choose not
to merge if the old and new entries were both on the stack, but the new
entry was in fewer registers than old one or if both locations were in
registers but the new one is no longer in a register that was not going
to be output.

Fixes golang#65005
@dmitshur dmitshur added this to the Backlog milestone Jan 9, 2024
@dmitshur dmitshur added NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. binary-size labels Jan 9, 2024
@mknyszek mknyszek moved this to In Progress in Go Compiler / Runtime Jan 17, 2024
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Labels
binary-size compiler/runtime Issues related to the Go compiler and/or runtime. NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one.
Projects
Go Compiler / Runtime
Status: In Progress
Milestone
Backlog
Development

Successfully merging a pull request may close this issue.

cmd/compile/internal/ssa: merge more loc lists ajwerner/go
3 participants
@ajwerner @dmitshur @gopherbot