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

[ajwerner]

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]

Change https://go.dev/cl/554515 mentions this issue: cmd/compile/internal/ssa: merge more loc lists

[ajwerner]

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%.