cmd/compile: stop generating block successor vars in rewrite rules

They are left over from the days before
we had BlockKindFirst and swapSuccessors.

Change-Id: I9259d53ac2821ca4d5de5dd520ca4b78f52ecad4
Reviewed-on: https://go-review.googlesource.com/41206
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Daniel Martí <mvdan@mvdan.cc>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

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

@@ -277,14 +277,6 @@ func genRules(arch arch) {
 				}
 			}
 
-			// assign successor names
-			succs := s[2:]
-			for i, a := range succs {
-				if a != "_" {
-					fmt.Fprintf(w, "%s := b.Succs[%d]\n", a, i)
-				}
-			}
-
 			if cond != "" {
 				fmt.Fprintf(w, "if !(%s) {\nbreak\n}\n", cond)
 			}
@@ -294,6 +286,7 @@ func genRules(arch arch) {
 			newsuccs := t[2:]
 
 			// Check if newsuccs is the same set as succs.
+			succs := s[2:]
 			m := map[string]bool{}
 			for _, succ := range succs {
 				if m[succ] {
@@ -333,9 +326,6 @@ func genRules(arch arch) {
 				}
 				fmt.Fprintln(w, "b.swapSuccessors()")
 			}
-			for i := 0; i < len(succs); i++ {
-				fmt.Fprintf(w, "_ = %s\n", newsuccs[i])
-			}
 
 			if *genLog {
 				fmt.Fprintf(w, "logRule(\"%s\")\n", rule.loc)

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

@@ -23705,13 +23705,9 @@ func rewriteBlockgeneric(b *Block) bool {
 				break
 			}
 			cond := v.Args[0]
-			yes := b.Succs[0]
-			no := b.Succs[1]
 			b.Kind = BlockIf
 			b.SetControl(cond)
 			b.swapSuccessors()
-			_ = no
-			_ = yes
 			return true
 		}
 		// match: (If (ConstBool [c]) yes no)
@@ -23723,15 +23719,11 @@ func rewriteBlockgeneric(b *Block) bool {
 				break
 			}
 			c := v.AuxInt
-			yes := b.Succs[0]
-			no := b.Succs[1]
 			if !(c == 1) {
 				break
 			}
 			b.Kind = BlockFirst
 			b.SetControl(nil)
-			_ = yes
-			_ = no
 			return true
 		}
 		// match: (If (ConstBool [c]) yes no)
@@ -23743,16 +23735,12 @@ func rewriteBlockgeneric(b *Block) bool {
 				break
 			}
 			c := v.AuxInt
-			yes := b.Succs[0]
-			no := b.Succs[1]
 			if !(c == 0) {
 				break
 			}
 			b.Kind = BlockFirst
 			b.SetControl(nil)
 			b.swapSuccessors()
-			_ = no
-			_ = yes
 			return true
 		}
 	}