Today, this interface conversion causes the struct literal
to be heap allocated:
var sink any
func example1() {
sink = S{1, 1}
}
For basic literals like integers that are directly used in
an interface conversion that would otherwise allocate, the compiler
is able to use read-only global storage (see #18704).
This CL extends that to struct and array literals as well by creating
read-only global storage that is able to represent for example S{1, 1},
and then using a pointer to that storage in the interface
when the interface conversion happens.
A more challenging example is:
func example2() {
v := S{1, 1}
sink = v
}
In this case, the struct literal is not directly part of the
interface conversion, but is instead assigned to a local variable.
To still avoid heap allocation in cases like this, in walk we
construct a cache that maps from expressions used in interface
conversions to earlier expressions that can be used to represent the
same value (via ir.ReassignOracle.StaticValue). This is somewhat
analogous to how we avoided heap allocation for basic literals in
CL 649077 earlier in our stack, though here we also need to do a
little more work to create the read-only global.
CL 649076 (also earlier in our stack) added most of the tests
along with debug diagnostics in convert.go to make it easier
to test this change.
See the writeup in #71359 for details.
Fixes#71359Fixes#71323
Updates #62653
Updates #53465
Updates #8618
Change-Id: I8924f0c69ff738ea33439bd6af7b4066af493b90
Reviewed-on: https://go-review.googlesource.com/c/go/+/649555
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Keith Randall <khr@golang.org>
Reviewed-by: David Chase <drchase@google.com>
Reviewed-by: Keith Randall <khr@google.com>
Currently, the integer value in the following interface conversion gets
heap allocated:
v := 1000
fmt.Println(v)
In contrast, this conversion does not currently cause the integer value
to be heap allocated:
fmt.Println(1000)
The second example is able to avoid heap allocation because of an
optimization in walk (by Josh in #18704 and related issues) that
recognizes a literal is being used. In the first example, that
optimization is currently thwarted by the literal getting assigned
to a local variable prior to use in the interface conversion.
This CL propagates constants to interface conversions like
in the first example to avoid heap allocations, instead using
a read-only global. The net effect is roughly turning the first example
into the second.
One place this comes up in practice currently is with logging or
debug prints. For example, if we have something like:
func conditionalDebugf(format string, args ...interface{}) {
if debugEnabled {
fmt.Fprintf(io.Discard, format, args...)
}
}
Prior to this CL, this integer is heap allocated, even when the
debugEnabled flag is false, and even when the compiler
inlines conditionalDebugf:
v := 1000
conditionalDebugf("hello %d", v)
With this CL, the integer here is no longer heap allocated, even when
the debugEnabled flag is enabled, because the compiler can now see that
it can use a read-only global.
See the writeup in #71359 for more details.
CL 649076 (earlier in our stack) added most of the tests
along with debug diagnostics in convert.go to make it easier
to test this change.
Updates #71359
Updates #62653
Updates #53465
Updates #8618
Change-Id: I19a51e74b36576ebb0b9cf599267cbd2bd847ce4
Reviewed-on: https://go-review.googlesource.com/c/go/+/649079
Auto-Submit: Keith Randall <khr@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: David Chase <drchase@google.com>
Reviewed-by: Keith Randall <khr@google.com>
This adds additional logging for the work that walk does to reduce
how often an interface conversion results in an allocation.
Also, as part of #71359, we will be updating how escape analysis and
walk handle basic literals, composite literals, and zero values,
so add some tests that uses this new logging.
By the end of our CL stack, we address all of these tests.
Updates #71359
Change-Id: I43fde8343d9aacaec1e05360417908014a86c8bd
Reviewed-on: https://go-review.googlesource.com/c/go/+/649076
Reviewed-by: Keith Randall <khr@golang.org>
Reviewed-by: Keith Randall <khr@google.com>
Reviewed-by: David Chase <drchase@google.com>
Auto-Submit: Keith Randall <khr@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
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