cmd/compile: absorb NEGV into branch on loong64

Removes 132 instructions from the go binary on loong64.

Change-Id: Ia02dc305b12f63a64f3f48d120ef852d45cc2a7b
Reviewed-on: https://go-review.googlesource.com/c/go/+/695115
Reviewed-by: Keith Randall <khr@google.com>
Reviewed-by: Keith Randall <khr@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Keith Randall <khr@golang.org>
Reviewed-by: David Chase <drchase@google.com>

src/cmd/compile/internal/ssa/_gen/LOONG64.rules

@@ -951,6 +951,10 @@
 (GEZ (MOVVconst [c]) yes no) && c >= 0 => (First yes no)
 (GEZ (MOVVconst [c]) yes no) && c <  0 => (First no yes)
 
+// absorb NEGV into branches
+(EQZ (NEGV x) yes no) => (EQZ x yes no)
+(NEZ (NEGV x) yes no) => (NEZ x yes no)
+
 // Convert branch with zero to more optimal branch zero.
 (BEQ  (MOVVconst [0]) cond yes no) => (EQZ cond yes no)
 (BEQ  cond (MOVVconst [0]) yes no) => (EQZ cond yes no)

src/cmd/compile/internal/ssa/rewriteLOONG64.go

@@ -11808,6 +11808,14 @@ func rewriteBlockLOONG64(b *Block) bool {
 			b.swapSuccessors()
 			return true
 		}
+		// match: (EQZ (NEGV x) yes no)
+		// result: (EQZ x yes no)
+		for b.Controls[0].Op == OpLOONG64NEGV {
+			v_0 := b.Controls[0]
+			x := v_0.Args[0]
+			b.resetWithControl(BlockLOONG64EQZ, x)
+			return true
+		}
 	case BlockLOONG64GEZ:
 		// match: (GEZ (MOVVconst [c]) yes no)
 		// cond: c >= 0
@@ -12135,6 +12143,14 @@ func rewriteBlockLOONG64(b *Block) bool {
 			b.Reset(BlockFirst)
 			return true
 		}
+		// match: (NEZ (NEGV x) yes no)
+		// result: (NEZ x yes no)
+		for b.Controls[0].Op == OpLOONG64NEGV {
+			v_0 := b.Controls[0]
+			x := v_0.Args[0]
+			b.resetWithControl(BlockLOONG64NEZ, x)
+			return true
+		}
 	}
 	return false
 }