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doc/go1.17: editing pass over the "Compiler" section

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Change-Id: I08c082f548daa7011a8dc42769371329684c90e6
Reviewed-on: https://go-review.googlesource.com/c/go/+/333609
Trust: Austin Clements <austin@google.com>
Trust: Dan Scales <danscales@google.com>
Reviewed-by: Dan Scales <danscales@google.com>
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Austin Clements 2021-07-09 16:22:32 -04:00
parent ab4085ce84
commit cfbd73ba33
1 changed files with 36 additions and 26 deletions
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doc/go1.17.html
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@ -401,30 +401,37 @@ func Foo() bool {
<p><!-- golang.org/issue/40724 -->
Go 1.17 implements a new way of passing function arguments and results using
registers instead of the stack. This work is enabled for Linux, macOS, and
Windows on the 64-bit x86 architecture (the <code>linux/amd64</code>,
<code>darwin/amd64</code>, <code>windows/amd64</code> ports). For a
representative set of Go packages and programs, benchmarking has shown
performance improvements of about 5%, and a typical reduction in binary size
of about 2%.
registers instead of the stack.
Benchmarks for a representative set of Go packages and programs show
performance improvements of about 5%, and a typical reduction in
binary size of about 2%.
This is currently enabled for Linux, macOS, and Windows on the
64-bit x86 architecture (the <code>linux/amd64</code>,
<code>darwin/amd64</code>, and <code>windows/amd64</code> ports).
</p>
<p>
This change does not affect the functionality of any safe Go code. It can affect
code outside the <a href="/doc/go1compat">compatibility guidelines</a> with
minimal impact. To maintain compatibility with existing assembly functions,
adapter functions converting between the new register-based calling convention
and the previous stack-based calling convention (also known as ABI wrappers)
are sometimes used. This is mostly invisible to users, except for assembly
functions that have their addresses taken in Go. Using <code>reflect.ValueOf(fn).Pointer()</code>
(or similar approaches such as via <code>unsafe.Pointer</code>) to get the address
of an assembly function will now return the address of the ABI wrapper. This is
mostly harmless, except for special-purpose assembly code (such as accessing
thread-local storage or requiring a special stack alignment). Assembly functions
called indirectly from Go via <code>func</code> values will now be made through
ABI wrappers, which may cause a very small performance overhead. Also, calling
Go functions from assembly may now go through ABI wrappers, with a very small
performance overhead.
This change does not affect the functionality of any safe Go code
and is designed to have no impact on most assembly code.
It may affect code that violates
the <a href="/pkg/unsafe#Pointer"><code>unsafe.Pointer</code></a>
rules when accessing function arguments, or that depends on
undocumented behavior involving comparing function code pointers.
To maintain compatibility with existing assembly functions, the
compiler generates adapter functions that convert between the new
register-based calling convention and the previous stack-based
calling convention.
These adapters are typically invisible to users, except that taking
the address of a Go function in assembly code or taking the address
of an assembly function in Go code
using <code>reflect.ValueOf(fn).Pointer()</code>
or <code>unsafe.Pointer</code> will now return the address of the
adapter.
Code that depends on the value of these code pointers may no longer
behave as expected.
Adapters also may cause a very small performance overhead in two
cases: calling an assembly function indirectly from Go via
a <code>func</code> value, and calling Go functions from assembly.
</p>
<p><!-- CL 304470 -->
@ -440,11 +447,14 @@ func Foo() bool {
</p>
<p><!-- CL 283112, golang.org/issue/28727 -->
Functions containing closures can now be inlined. One effect of this change is
that a function with a closure may actually produce a distinct closure function
for each place that the function is inlined. Hence, this change could reveal
bugs where Go functions are compared (incorrectly) by pointer value. Go
functions are by definition not comparable.
Functions containing closures can now be inlined.
One effect of this change is that a function with a closure may
produce a distinct closure code pointer for each place that the
function is inlined.
Go function values are not directly comparable, but this change
could reveal bugs in code that uses <code>reflect</code>
or <code>unsafe.Pointer</code> to bypass this language restriction
and compare functions by code pointer.
</p>
<h2 id="library">Core library</h2>