cmd/compile: sparse conditional constant propagation

sparse conditional constant propagation can discover optimization
opportunities that cannot be found by just combining constant folding
and constant propagation and dead code elimination separately.

Updates #59399

Author: y1yang0

src/cmd/compile/internal/ssa/_gen/genericOps.go

@@ -643,6 +643,8 @@ var genericOps = []opData{
 //    Plain                []            [next]
 //       If   [boolean Value]      [then, else]
 //    First                []   [always, never]
+//    Defer             [mem]  [nopanic, panic]                  (control opcode should be OpStaticCall to runtime.deferproc)
+//JumpTable   [boolean Value]  [succ1,succ2,..]
 
 var genericBlocks = []blockData{
 	{name: "Plain"},                  // a single successor

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

@@ -112,13 +112,6 @@ func (e Edge) String() string {
 }
 
 // BlockKind is the kind of SSA block.
-//
-//	  kind          controls        successors
-//	------------------------------------------
-//	  Exit      [return mem]                []
-//	 Plain                []            [next]
-//	    If   [boolean Value]      [then, else]
-//	 Defer             [mem]  [nopanic, panic]  (control opcode should be OpStaticCall to runtime.deferproc)
 type BlockKind int16
 
 // short form print

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

@@ -459,6 +459,7 @@ var passes = [...]pass{
 	{name: "number lines", fn: numberLines, required: true},
 	{name: "early phielim", fn: phielim},
 	{name: "early copyelim", fn: copyelim},
+	{name: "sccp", fn: sccp},
 	{name: "early deadcode", fn: deadcode}, // remove generated dead code to avoid doing pointless work during opt
 	{name: "short circuit", fn: shortcircuit},
 	{name: "decompose user", fn: decomposeUser, required: true},