cmd/compile: fix the error of absorbing boolean tests into block(FGE, FGT)

The CL 164718 mistyped the comparison flags. The rules for floating
point comparison should be GreaterThanF and GreaterEqualF. Fortunately,
the wrong optimizations were overwritten by other integer rules, so the
issue won't cause failure but just some performance impact.

The fixed CL optimizes the floating point test as follows.

source code: func foo(f float64) bool { return f > 4 || f < -4}
previous version: "FCMPD", "CSET\tGT", "CBZ"
fixed version: "FCMPD", BLE"

Add the test case.

Change-Id: Iea954fdbb8272b2d642dae0f816dc77286e6e1fa
Reviewed-on: https://go-review.googlesource.com/c/go/+/177121
Reviewed-by: Ben Shi <[email protected]>
Reviewed-by: Cherry Zhang <[email protected]>
Run-TryBot: Ben Shi <[email protected]>
TryBot-Result: Gobot Gobot <[email protected]>

Author: zhangfannie

src/cmd/compile/internal/ssa/gen/ARM64.rules

@@ -630,8 +630,8 @@
 (NZ (GreaterEqualU cc) yes no) -> (UGE cc yes no)
 (NZ (LessThanF cc) yes no) -> (FLT cc yes no)
 (NZ (LessEqualF cc) yes no) -> (FLE cc yes no)
-(NZ (GreaterThan cc) yes no) -> (FGT cc yes no)
-(NZ (GreaterEqual cc) yes no) -> (FGE cc yes no)
+(NZ (GreaterThanF cc) yes no) -> (FGT cc yes no)
+(NZ (GreaterEqualF cc) yes no) -> (FGE cc yes no)
 
 (EQ (CMPWconst [0] x:(ANDconst [c] y)) yes no) && x.Uses == 1 -> (EQ (TSTWconst [c] y) yes no)
 (NE (CMPWconst [0] x:(ANDconst [c] y)) yes no) && x.Uses == 1 -> (NE (TSTWconst [c] y) yes no)

src/cmd/compile/internal/ssa/rewriteARM64.go

@@ -117,6 +117,11 @@ func FusedSub64_b(x, y, z float64) float64 {
 	return z - x*y
 }
 
+func Cmp(f float64) bool {
+	// arm64:"FCMPD","BLE",-"CSET\tGT",-"CBZ"
+	return f > 4 || f < -4
+}
+
 // ---------------- //
 //    Non-floats    //
 // ---------------- //