[dev.ssa] cmd/compile: split op rewrites into separate functions

The single value rewrite function is too big.  Some compilers
fail on it (out of memory, branch offset too large).  Break it
up into a rewrite function per op.

Change-Id: Iede697c8a1a3a22b485cd0dc85d3e233160c89c2
Reviewed-on: https://go-review.googlesource.com/16347
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Todd Neal <todd@tneal.org>

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

@@ -134,6 +134,13 @@ func genRules(arch arch) {
 		log.Fatalf("unbalanced rule at line %d: %v\n", lineno, rule)
 	}
 
+	// Order all the ops.
+	var ops []string
+	for op := range oprules {
+		ops = append(ops, op)
+	}
+	sort.Strings(ops)
+
 	// Start output buffer, write header.
 	w := new(bytes.Buffer)
 	fmt.Fprintf(w, "// autogenerated from gen/%s.rules: do not edit!\n", arch.name)
@@ -145,18 +152,23 @@ func genRules(arch arch) {
 	fmt.Fprintln(w, "import \"math\"")
 	fmt.Fprintln(w, "var _ = math.MinInt8 // in case not otherwise used")
 
+	// Main rewrite routine is a switch on v.Op.
 	fmt.Fprintf(w, "func rewriteValue%s(v *Value, config *Config) bool {\n", arch.name)
-	fmt.Fprintln(w, "b := v.Block")
-
-	// generate code for each rule
 	fmt.Fprintf(w, "switch v.Op {\n")
-	var ops []string
-	for op := range oprules {
-		ops = append(ops, op)
-	}
-	sort.Strings(ops)
 	for _, op := range ops {
 		fmt.Fprintf(w, "case %s:\n", opName(op, arch))
+		fmt.Fprintf(w, "return rewriteValue%s_%s(v, config)\n", arch.name, opName(op, arch))
+	}
+	fmt.Fprintf(w, "}\n")
+	fmt.Fprintf(w, "return false\n")
+	fmt.Fprintf(w, "}\n")
+
+	// Generate a routine per op.  Note that we don't make one giant routine
+	// because it is too big for some compilers.
+	for _, op := range ops {
+		fmt.Fprintf(w, "func rewriteValue%s_%s(v *Value, config *Config) bool {\n", arch.name, opName(op, arch))
+		fmt.Fprintln(w, "b := v.Block")
+		fmt.Fprintln(w, "_ = b")
 		for _, rule := range oprules[op] {
 			// Note: we use a hash to identify the rule so that its
 			// identity is invariant to adding/removing rules elsewhere
@@ -188,12 +200,12 @@ func genRules(arch arch) {
 			fmt.Fprintf(w, "goto end%s\n", rulehash) // use label
 			fmt.Fprintf(w, "end%s:;\n", rulehash)
 		}
+		fmt.Fprintf(w, "return false\n")
+		fmt.Fprintf(w, "}\n")
 	}
-	fmt.Fprintf(w, "}\n")
-	fmt.Fprintf(w, "return false\n")
-	fmt.Fprintf(w, "}\n")
 
-	// Generate block rewrite function.
+	// Generate block rewrite function.  There are only a few block types
+	// so we can make this one function with a switch.
 	fmt.Fprintf(w, "func rewriteBlock%s(b *Block) bool {\n", arch.name)
 	fmt.Fprintf(w, "switch b.Kind {\n")
 	ops = nil