cmd/compile: add patterns to improve PPC64 FP comparisons

Uncommented 4 comparison rules of this form:
(NE (CMPWconst [0] (FLessThan cc)) yes no) -> (FLT cc yes no)

Fixes #17507.

Change-Id: I74f34f13526aeee619711c8281a66652d90a962a
Reviewed-on: https://go-review.googlesource.com/31612
Run-TryBot: David Chase <drchase@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>

src/cmd/compile/internal/ssa/gen/PPC64.rules

@@ -361,10 +361,10 @@
 (NE (CMPWconst [0] (LessEqual cc)) yes no) -> (LE cc yes no)
 (NE (CMPWconst [0] (GreaterThan cc)) yes no) -> (GT cc yes no)
 (NE (CMPWconst [0] (GreaterEqual cc)) yes no) -> (GE cc yes no)
-// (NE (CMPWconst [0] (FLessThan cc)) yes no) -> (FLT cc yes no)
-// (NE (CMPWconst [0] (FLessEqual cc)) yes no) -> (FLE cc yes no)
-// (NE (CMPWconst [0] (FGreaterThan cc)) yes no) -> (FGT cc yes no)
-// (NE (CMPWconst [0] (FGreaterEqual cc)) yes no) -> (FGE cc yes no)
+(NE (CMPWconst [0] (FLessThan cc)) yes no) -> (FLT cc yes no)
+(NE (CMPWconst [0] (FLessEqual cc)) yes no) -> (FLE cc yes no)
+(NE (CMPWconst [0] (FGreaterThan cc)) yes no) -> (FGT cc yes no)
+(NE (CMPWconst [0] (FGreaterEqual cc)) yes no) -> (FGE cc yes no)
 
 // Elide compares of bit tests // TODO need to make both CC and result of ANDCC available.
 (EQ (CMPconst [0] (ANDconst [c] x)) yes no) -> (EQ (ANDCCconst [c] x) yes no)

src/cmd/compile/internal/ssa/rewritePPC64.go

@@ -10584,6 +10584,102 @@ func rewriteBlockPPC64(b *Block, config *Config) bool {
 			_ = no
 			return true
 		}
+		// match: (NE (CMPWconst [0] (FLessThan cc)) yes no)
+		// cond:
+		// result: (FLT cc yes no)
+		for {
+			v := b.Control
+			if v.Op != OpPPC64CMPWconst {
+				break
+			}
+			if v.AuxInt != 0 {
+				break
+			}
+			v_0 := v.Args[0]
+			if v_0.Op != OpPPC64FLessThan {
+				break
+			}
+			cc := v_0.Args[0]
+			yes := b.Succs[0]
+			no := b.Succs[1]
+			b.Kind = BlockPPC64FLT
+			b.SetControl(cc)
+			_ = yes
+			_ = no
+			return true
+		}
+		// match: (NE (CMPWconst [0] (FLessEqual cc)) yes no)
+		// cond:
+		// result: (FLE cc yes no)
+		for {
+			v := b.Control
+			if v.Op != OpPPC64CMPWconst {
+				break
+			}
+			if v.AuxInt != 0 {
+				break
+			}
+			v_0 := v.Args[0]
+			if v_0.Op != OpPPC64FLessEqual {
+				break
+			}
+			cc := v_0.Args[0]
+			yes := b.Succs[0]
+			no := b.Succs[1]
+			b.Kind = BlockPPC64FLE
+			b.SetControl(cc)
+			_ = yes
+			_ = no
+			return true
+		}
+		// match: (NE (CMPWconst [0] (FGreaterThan cc)) yes no)
+		// cond:
+		// result: (FGT cc yes no)
+		for {
+			v := b.Control
+			if v.Op != OpPPC64CMPWconst {
+				break
+			}
+			if v.AuxInt != 0 {
+				break
+			}
+			v_0 := v.Args[0]
+			if v_0.Op != OpPPC64FGreaterThan {
+				break
+			}
+			cc := v_0.Args[0]
+			yes := b.Succs[0]
+			no := b.Succs[1]
+			b.Kind = BlockPPC64FGT
+			b.SetControl(cc)
+			_ = yes
+			_ = no
+			return true
+		}
+		// match: (NE (CMPWconst [0] (FGreaterEqual cc)) yes no)
+		// cond:
+		// result: (FGE cc yes no)
+		for {
+			v := b.Control
+			if v.Op != OpPPC64CMPWconst {
+				break
+			}
+			if v.AuxInt != 0 {
+				break
+			}
+			v_0 := v.Args[0]
+			if v_0.Op != OpPPC64FGreaterEqual {
+				break
+			}
+			cc := v_0.Args[0]
+			yes := b.Succs[0]
+			no := b.Succs[1]
+			b.Kind = BlockPPC64FGE
+			b.SetControl(cc)
+			_ = yes
+			_ = no
+			return true
+		}
 		// match: (NE (CMPconst [0] (ANDconst [c] x)) yes no)
 		// cond:
 		// result: (NE (ANDCCconst [c] x) yes no)