cmd/compile: don't rewrite (CMP (AND x y) 0) to TEST if AND has other uses

If the AND has other uses, we end up saving an argument to the AND
in another register, so we can use it for the TEST. No point in doing that.

Change-Id: I73444a6aeddd6f55e2328ce04d77c3e6cf4a83e0
Reviewed-on: https://go-review.googlesource.com/c/go/+/241280
Run-TryBot: Keith Randall <khr@golang.org>
Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

1 files changed, 24 insertions, 0 deletions

diff --git a/test/codegen/logic.go b/test/codegen/logic.go
new file mode 100644
index 0000000000..9afdfd760f
--- /dev/null
+++ b/test/codegen/logic.go
@@ -0,0 +1,24 @@
+// asmcheck
+
+// 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.
+
+package codegen
+
+var gx, gy int
+
+// Test to make sure that (CMPQ (ANDQ x y) [0]) does not get rewritten to
+// (TESTQ x y) if the ANDQ has other uses. If that rewrite happens, then one
+// of the args of the ANDQ needs to be saved so it can be used as the arg to TESTQ.
+func andWithUse(x, y int) int {
+	// Load x,y into registers, so those MOVQ will not appear at the z := x&y line.
+	gx, gy = x, y
+	// amd64:-"MOVQ"
+	z := x & y
+	if z == 0 {
+		return 77
+	}
+	// use z by returning it
+	return z
+}