all: AVX-512 (#217)

Extends avo to support most AVX-512 instruction sets.

The instruction type is extended to support suffixes. The K family of opmask
registers is added to the register package, and the operand package is updated
to support the new operand types. Move instruction deduction in `Load` and
`Store` is extended to support KMOV* and VMOV* forms.

Internal code generation packages were overhauled. Instruction database loading
required various messy changes to account for the additional complexities of the
AVX-512 instruction sets. The internal/api package was added to introduce a
separation between instruction forms in the database, and the functions avo
provides to create them. This was required since with instruction suffixes there
is no longer a one-to-one mapping between instruction constructors and opcodes.

AVX-512 bloated generated source code size substantially, initially increasing
compilation and CI test times to an unacceptable level. Two changes were made to
address this:

1.  Instruction constructors in the `x86` package moved to an optab-based
    approach. This compiles substantially faster than the verbose code
    generation we had before.

2.  The most verbose code-generated tests are moved under build tags and
    limited to a stress test mode. Stress test builds are run on
    schedule but not in regular CI.

An example of AVX-512 accelerated 16-lane MD5 is provided to demonstrate and
test the new functionality.

Updates #20 #163 #229

Co-authored-by: Vaughn Iverson <vsivsi@yahoo.com>

ir/ir.go

@@ -37,6 +37,7 @@ func NewComment(lines ...string) *Comment {
 // Instruction is a single instruction in a function.
 type Instruction struct {
 	Opcode   string
+	Suffixes []string
 	Operands []operand.Op
 
 	Inputs  []operand.Op
@@ -61,6 +62,15 @@ type Instruction struct {
 
 func (i *Instruction) node() {}
 
+// OpcodeWithSuffixes returns the full opcode, including dot-separated suffixes.
+func (i *Instruction) OpcodeWithSuffixes() string {
+	opcode := i.Opcode
+	for _, s := range i.Suffixes {
+		opcode += "." + s
+	}
+	return opcode
+}
+
 // IsUnconditionalBranch reports whether i is an unconditional branch.
 func (i Instruction) IsUnconditionalBranch() bool {
 	return i.IsBranch && !i.IsConditional