cmd/compile: enable lateLower pass on PPC64

This allows new rules to be added which would otherwise
greatly overcomplicate the generic rules, like CC opcode
conversion or zero register simplification.

Change-Id: I1533f0fa07815aff99ed8ab890077bd22a3bfbf5
Reviewed-on: https://go-review.googlesource.com/c/go/+/442595
Reviewed-by: Lynn Boger <laboger@linux.vnet.ibm.com>
Run-TryBot: Paul Murphy <murp@ibm.com>
Reviewed-by: David Chase <drchase@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Bryan Mills <bcmills@google.com>

src/cmd/compile/internal/ssa/_gen/PPC64latelower.rules

@@ -0,0 +1,5 @@
+// Copyright 2022 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 file contains rules used by the laterLower pass.

src/cmd/compile/internal/ssa/config.go

@@ -244,6 +244,7 @@ func NewConfig(arch string, types Types, ctxt *obj.Link, optimize, softfloat boo
 		c.RegSize = 8
 		c.lowerBlock = rewriteBlockPPC64
 		c.lowerValue = rewriteValuePPC64
+		c.lateLowerValue = rewriteValuePPC64latelower
 		c.registers = registersPPC64[:]
 		c.gpRegMask = gpRegMaskPPC64
 		c.fpRegMask = fpRegMaskPPC64