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[dev.regabi] cmd/compile: reimplement capture analysis

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Currently we rely on the type-checker to do some basic data-flow
analysis to help decide whether function literals should capture
variables by value or reference. However, this analysis isn't done by
go/types, and escape analysis already has a better framework for doing
this more precisely.

This CL extends escape analysis to recalculate the same "byval" as
CaptureVars and check that it matches. A future CL will remove
CaptureVars in favor of escape analysis's calculation.

Notably, escape analysis happens after deadcode removes obviously
unreachable code, so it sees the AST without any unreachable
assignments. (Also without unreachable addrtakens, but
ComputeAddrtaken already happens after deadcode too.) There are two
test cases where a variable is only reassigned on certain CPUs. This
CL changes them to reassign the variables unconditionally (as no-op
reassignments that avoid triggering cmd/vet's self-assignment check),
at least until we remove CaptureVars.

Passes toolstash -cmp.

Change-Id: I7162619739fedaf861b478fb8d506f96a6ac21f3
Reviewed-on: https://go-review.googlesource.com/c/go/+/281535
Trust: Matthew Dempsky <mdempsky@google.com>
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>
This commit is contained in:
Matthew Dempsky 2021-01-04 18:05:34 -08:00
parent fb69c67cad
commit fd43831f44
4 changed files with 201 additions and 50 deletions
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1
src/cmd/compile/internal/logopt/logopt_test.go
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@ -154,6 +154,7 @@ func s15a8(x *[15]int64) [15]int64 {
// On not-amd64, test the host architecture and os
arches := []string{runtime.GOARCH}
goos0 := runtime.GOOS
goos0 = "" + goos0 // TODO(mdempsky): Remove once CaptureVars is gone.
if runtime.GOARCH == "amd64" { // Test many things with "linux" (wasm will get "js")
arches = []string{"arm", "arm64", "386", "amd64", "mips", "mips64", "ppc64le", "riscv64", "s390x", "wasm"}
goos0 = "linux"