cmd/compile: make math/bits.RotateLeft* an intrinsic on amd64

Previously, pattern matching was good enough to achieve good performance
for the RotateLeft* functions, but the inlining cost for them was much
too high. Make RotateLeft* intrinsic on amd64 as a stop-gap for now to
reduce inlining costs.

This should be done (or at least looked at) for other architectures
as well.

Updates golang/go#17566

Change-Id: I6a106ff00b6c4e3f490650af3e083ed2be00c819
Reviewed-on: https://go-review.googlesource.com/132435
Run-TryBot: Andrew Bonventre <andybons@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: David Chase <drchase@google.com>

1 files changed, 28 insertions, 0 deletions

diff --git a/test/inline_math_bits_rotate.go b/test/inline_math_bits_rotate.go
new file mode 100644
index 0000000000..a0341ea497
--- /dev/null
+++ b/test/inline_math_bits_rotate.go
@@ -0,0 +1,28 @@
+// +build amd64
+// errorcheck -0 -m
+
+// Copyright 2018 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Test that inlining of math/bits.RotateLeft* treats those calls as intrinsics.
+
+package p
+
+import "math/bits"
+
+var (
+	x8  uint8
+	x16 uint16
+	x32 uint32
+	x64 uint64
+	x   uint
+)
+
+func f() { // ERROR "can inline f"
+	x8 = bits.RotateLeft8(x8, 1)
+	x16 = bits.RotateLeft16(x16, 1)
+	x32 = bits.RotateLeft32(x32, 1)
+	x64 = bits.RotateLeft64(x64, 1)
+	x = bits.RotateLeft(x, 1)
+}