cmd/compile: add | operator to make rewrite rules more succinct

Instead of

(And64 x x) -> x
(And32 x x) -> x
(And16 x x) -> x
(And8  x x) -> x

we can now do:

(And(64|32|16|8) x x) -> x

Any part of an opcode can have a parenthesized, |-separated list of possibilites.
The rule is then expanded using each piece of the | combo.
If there are multiple | clauses, they get expanded in tandem.
(All the first positions, then all the second positions, etc.)
All places | opcodes appear must have the same count.

A more complicated example:

(MOV(L|SS)load [off1] {sym1} (LEAQ4 [off2] {sym2} ptr idx) mem) && is32Bit(off1+off2) && canMergeSym(sym1, sym2) ->
	(MOV(L|SS)loadidx4 [off1+off2] {mergeSym(sym1,sym2)} ptr idx mem)

This meta-rule generates 2 rules, a MOVL and a MOVSS rule.

This CL is carefully orchestrated to not change the generated rules file at all.
In some cases, this means we can't align the rules nicely because it changes
the whitespace in the generated code.  I'll clean that up as a separate step.

There are many more opportunites to compactify rules using this new mechanism.
I've just done some examples, there's more to do.

Change-Id: I8a5e748cd0761ccbb12d09b01925b2f1f4b2f608
Reviewed-on: https://go-review.googlesource.com/86595
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>

src/cmd/compile/internal/ssa/gen/rulegen.go

@@ -119,9 +119,10 @@ func genRules(arch arch) {
 		}
 
 		loc := fmt.Sprintf("%s.rules:%d", arch.name, ruleLineno)
-		for _, crule := range commute(rule, arch) {
-			r := Rule{rule: crule, loc: loc}
-			if rawop := strings.Split(crule, " ")[0][1:]; isBlock(rawop, arch) {
+		for _, rule2 := range expandOr(rule) {
+			for _, rule3 := range commute(rule2, arch) {
+				r := Rule{rule: rule3, loc: loc}
+				if rawop := strings.Split(rule3, " ")[0][1:]; isBlock(rawop, arch) {
 					blockrules[rawop] = append(blockrules[rawop], r)
 				} else {
 					// Do fancier value op matching.
@@ -131,6 +132,7 @@ func genRules(arch arch) {
 					oprules[opname] = append(oprules[opname], r)
 				}
 			}
+		}
 		rule = ""
 		ruleLineno = 0
 	}
@@ -659,7 +661,6 @@ func extract(val string) (op string, typ string, auxint string, aux string, args
 // It returns the op and unparsed strings for typ, auxint, and aux restrictions and for all args.
 // oparch is the architecture that op is located in, or "" for generic.
 func parseValue(val string, arch arch, loc string) (op opData, oparch string, typ string, auxint string, aux string, args []string) {
-
 	// Resolve the op.
 	var s string
 	s, typ, auxint, aux, args = extract(val)
@@ -784,6 +785,48 @@ func isVariable(s string) bool {
 	return b
 }
 
+// opRegexp is a regular expression to find the opcode portion of s-expressions.
+var opRegexp = regexp.MustCompile(`[(]\w*[(](\w+[|])+\w+[)]\w* `)
+
+// expandOr converts a rule into multiple rules by expanding | ops.
+func expandOr(r string) []string {
+	// Find every occurrence of |-separated things at the opcode position.
+	// They look like (MOV(B|W|L|Q|SS|SD)load
+	// Note: there might be false positives in parts of rules that are Go code
+	// (e.g. && conditions, AuxInt expressions, etc.).  There are currently no
+	// such false positives, so I'm not too worried about it.
+	// Generate rules selecting one case from each |-form.
+
+	// Count width of |-forms.  They must match.
+	n := 1
+	for _, s := range opRegexp.FindAllString(r, -1) {
+		c := strings.Count(s, "|") + 1
+		if c == 1 {
+			continue
+		}
+		if n > 1 && n != c {
+			log.Fatalf("'|' count doesn't match in %s: both %d and %d\n", r, n, c)
+		}
+		n = c
+	}
+	if n == 1 {
+		// No |-form in this rule.
+		return []string{r}
+	}
+	res := make([]string, n)
+	for i := 0; i < n; i++ {
+		res[i] = opRegexp.ReplaceAllStringFunc(r, func(s string) string {
+			if strings.Count(s, "|") == 0 {
+				return s
+			}
+			s = s[1 : len(s)-1] // remove leading "(" and trailing " "
+			x, y := strings.Index(s, "("), strings.Index(s, ")")
+			return "(" + s[:x] + strings.Split(s[x+1:y], "|")[i] + s[y+1:] + " "
+		})
+	}
+	return res
+}
+
 // commute returns all equivalent rules to r after applying all possible
 // argument swaps to the commutable ops in r.
 // Potentially exponential, be careful.