cmd/compile: generate makechan calls with int arguments

Where possible generate calls to runtime makechan with int arguments
during compile time instead of makechan with int64 arguments.

This eliminates converting arguments for calls to makechan with
int64 arguments for platforms where int64 values do not fit into
arguments of type int.

A similar optimization for makeslice was introduced in CL
golang.org/cl/27851.

386:
name                old time/op  new time/op  delta
MakeChan/Byte       52.4ns ± 6%  45.0ns ± 1%  -14.14%  (p=0.000 n=10+10)
MakeChan/Int        54.5ns ± 1%  49.1ns ± 1%   -9.87%  (p=0.000 n=10+10)
MakeChan/Ptr         150ns ± 1%   143ns ± 0%   -4.38%  (p=0.000 n=9+7)
MakeChan/Struct/0   49.2ns ± 2%  43.2ns ± 2%  -12.27%  (p=0.000 n=10+10)
MakeChan/Struct/32  81.7ns ± 2%  76.2ns ± 1%   -6.71%  (p=0.000 n=10+10)
MakeChan/Struct/40  88.4ns ± 2%  82.5ns ± 2%   -6.60%  (p=0.000 n=10+10)

AMD64:
name                old time/op  new time/op  delta
MakeChan/Byte       83.4ns ± 8%  80.8ns ± 3%    ~     (p=0.171 n=10+10)
MakeChan/Int         101ns ± 3%   101ns ± 2%    ~     (p=0.412 n=10+10)
MakeChan/Ptr         128ns ± 1%   128ns ± 1%    ~     (p=0.191 n=10+10)
MakeChan/Struct/0   67.6ns ± 3%  68.7ns ± 4%    ~     (p=0.224 n=10+10)
MakeChan/Struct/32   138ns ± 1%   139ns ± 1%    ~     (p=0.185 n=10+9)
MakeChan/Struct/40   154ns ± 1%   154ns ± 1%  -0.55%  (p=0.027 n=10+9)

Change-Id: Ie854cb066007232c5e9f71ea7d6fe27e81a9c050
Reviewed-on: https://go-review.googlesource.com/55140
Run-TryBot: Martin Möhrmann <moehrmann@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>

1 files changed, 41 insertions, 2 deletions

diff --git a/test/chancap.go b/test/chancap.go
index b3e40233f5..b08478a13c 100644
--- a/test/chancap.go
+++ b/test/chancap.go
@@ -8,8 +8,17 @@
 
 package main
 
+import (
+	"strings"
+	"unsafe"
+)
+
+type T chan int
+
+const ptrSize = unsafe.Sizeof((*byte)(nil))
+
 func main() {
-	c := make(chan int, 10)
+	c := make(T, 10)
 	if len(c) != 0 || cap(c) != 10 {
 		println("chan len/cap ", len(c), cap(c), " want 0 10")
 		panic("fail")
@@ -23,9 +32,39 @@ func main() {
 		panic("fail")
 	}
 
-	c = make(chan int)
+	c = make(T)
 	if len(c) != 0 || cap(c) != 0 {
 		println("chan len/cap ", len(c), cap(c), " want 0 0")
 		panic("fail")
 	}
+
+	n := -1
+	shouldPanic("makechan: size out of range", func() { _ = make(T, n) })
+	shouldPanic("makechan: size out of range", func() { _ = make(T, int64(n)) })
+	if ptrSize == 8 {
+		n = 1 << 20
+		n <<= 20
+		shouldPanic("makechan: size out of range", func() { _ = make(T, n) })
+		n <<= 20
+		shouldPanic("makechan: size out of range", func() { _ = make(T, n) })
+	} else {
+		n = 1<<31 - 1
+		shouldPanic("makechan: size out of range", func() { _ = make(T, n) })
+		shouldPanic("makechan: size out of range", func() { _ = make(T, int64(n)) })
+	}
+}
+
+func shouldPanic(str string, f func()) {
+	defer func() {
+		err := recover()
+		if err == nil {
+			panic("did not panic")
+		}
+		s := err.(error).Error()
+		if !strings.Contains(s, str) {
+			panic("got panic " + s + ", want " + str)
+		}
+	}()
+
+	f()
 }