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[dev.regabi] cmd/compile: earlier deadcode removal

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This CL moves the general deadcode-removal pass to before computing
Addrtaken, which allows variables to still be converted to SSA if
their address is only taken in unreachable code paths (e.g., the "&mp"
expression in the "if false" block in runtime/os_linux.go:newosproc).

This doesn't pass toolstash -cmp, because it allows SSA to better
optimize some code.

Change-Id: I43e54acc02fdcbad8eb6493283f355aa1ee0de84
Reviewed-on: https://go-review.googlesource.com/c/go/+/280992
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 2021-01-01 01:32:46 -08:00
parent 68e6fa4f68
commit 6ddbc75efd
1 changed files with 8 additions and 8 deletions
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16
src/cmd/compile/internal/gc/main.go
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@ -213,6 +213,14 @@ func Main(archInit func(*ssagen.ArchInfo)) {
typecheck.Export(initTask)
}
// Eliminate some obviously dead code.
// Must happen after typechecking.
for _, n := range typecheck.Target.Decls {
if n.Op() == ir.ODCLFUNC {
deadcode.Func(n.(*ir.Func))
}
}
// Compute Addrtaken for names.
// We need to wait until typechecking is done so that when we see &x[i]
// we know that x has its address taken if x is an array, but not if x is a slice.
@ -224,14 +232,6 @@ func Main(archInit func(*ssagen.ArchInfo)) {
}
typecheck.IncrementalAddrtaken = true
// Eliminate some obviously dead code.
// Must happen after typechecking.
for _, n := range typecheck.Target.Decls {
if n.Op() == ir.ODCLFUNC {
deadcode.Func(n.(*ir.Func))
}
}
// Decide how to capture closed variables.
// This needs to run before escape analysis,
// because variables captured by value do not escape.