cmd/compile: add BVC/BVS to branch ops in ppc64/prog.go

Includes test case shown to fail with unpatched compiler.

Fixes #17005.

Change-Id: I49b7b1a3f02736d85846a2588018b73f68d50320
Reviewed-on: https://go-review.googlesource.com/28573
Run-TryBot: David Chase <drchase@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Minux Ma <minux@golang.org>

src/cmd/compile/internal/ppc64/prog.go

@@ -112,6 +112,8 @@ var progtable = [ppc64.ALAST & obj.AMask]obj.ProgInfo{
 	// Jumps
 	ppc64.ABR & obj.AMask:  {Flags: gc.Jump | gc.Break},
 	ppc64.ABL & obj.AMask:  {Flags: gc.Call},
+	ppc64.ABVS & obj.AMask: {Flags: gc.Cjmp},
+	ppc64.ABVC & obj.AMask: {Flags: gc.Cjmp},
 	ppc64.ABEQ & obj.AMask: {Flags: gc.Cjmp},
 	ppc64.ABNE & obj.AMask: {Flags: gc.Cjmp},
 	ppc64.ABGE & obj.AMask: {Flags: gc.Cjmp},

test/fixedbugs/issue17005.go

+// compile
+
+// Copyright 2016 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.
+
+// This tickles (a version of) the PPC64 back end to
+// emit a BVS instruction.
+
+package foo
+
+type Flag int
+
+const (
+	Identity  Flag = iota - 2 // H is the identity matrix; no rotation is needed.
+	Rescaling                 // H specifies rescaling.
+)
+
+type DrotmParams struct {
+	Flag
+}
+
+func Drotmg(d1, d2, x1, y1 float64) (p DrotmParams, rd1, rd2, rx1 float64) {
+
+	const (
+		gam    = 4.0
+		gamsq  = 16.0
+		rgamsq = 5e-8
+	)
+
+	if d1 < 0 {
+		p.Flag = Rescaling
+		return
+	}
+
+	for rd1 <= rgamsq || rd1 >= gamsq {
+		if rd1 <= rgamsq {
+			rd1 *= gam * gam
+			rx1 /= gam
+		} else {
+			rd1 /= gam * gam
+			rx1 *= gam
+		}
+	}
+	return
+}