cmd/compile: fix conditional move rule on PPC64

Similar to CL 456556 but for ppc64 instead of arm64.

Change docs about how booleans are stored in registers for ppc64.
We now don't promise to keep the upper bits zeroed; they might be junk.

To test, I changed the boolean generation instructions (MOVBZload* and ISEL*
with boolean type) to OR in 0x100 to the result. all.bash still passed,
so I think nothing else is depending on the upper bits of booleans.

Update #57184

Change-Id: Ie66f8934a0dafa34d0a8c2a37324868d959a852c
Reviewed-on: https://go-review.googlesource.com/c/go/+/456437
Run-TryBot: Keith Randall <khr@golang.org>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Reviewed-by: Keith Randall <khr@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: KAMPANAT THUMWONG (KONG PC) <1992kongpc.kth@gmail.com>
Run-TryBot: Archana Ravindar <aravind5@in.ibm.com>

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

@@ -409,9 +409,9 @@
 ((EQ|NE|LT|LE|GT|GE) (CMPconst [0] z:(XOR x y)) yes no) && z.Uses == 1 => ((EQ|NE|LT|LE|GT|GE) (Select1 <types.TypeFlags> (XORCC x y)) yes no)
 
 // Only lower after bool is lowered. It should always lower. This helps ensure the folding below happens reliably.
-(CondSelect x y bool) && flagArg(bool) == nil => (ISEL [6] x y (CMPWconst [0] bool))
+(CondSelect x y bool) && flagArg(bool) == nil => (ISEL [6] x y (Select1 <types.TypeFlags> (ANDCCconst [1] bool)))
 // Fold any CR -> GPR -> CR transfers when applying the above rule.
-(ISEL [6] x y (CMPWconst [0] (ISELB [c] one cmp))) => (ISEL [c] x y cmp)
+(ISEL [6] x y (Select1 (ANDCCconst [1] (ISELB [c] one cmp)))) => (ISEL [c] x y cmp)
 
 // Lowering loads
 (Load <t> ptr mem) && (is64BitInt(t) || isPtr(t)) => (MOVDload ptr mem)

src/cmd/compile/internal/ssa/_gen/PPC64Ops.go

@@ -8,8 +8,8 @@ import "strings"
 
 // Notes:
 //  - Less-than-64-bit integer types live in the low portion of registers.
-//    For now, the upper portion is junk; sign/zero-extension might be optimized in the future, but not yet.
-//  - Boolean types are zero or 1; stored in a byte, but loaded with AMOVBZ so the upper bytes of a register are zero.
+//    The upper portion is junk.
+//  - Boolean types are zero or 1; stored in a byte, with upper bytes of the register containing junk.
 //  - *const instructions may use a constant larger than the instruction can encode.
 //    In this case the assembler expands to multiple instructions and uses tmp
 //    register (R31).

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

@@ -1172,9 +1172,10 @@ func rewriteValuePPC64_OpCondSelect(v *Value) bool {
 	v_1 := v.Args[1]
 	v_0 := v.Args[0]
 	b := v.Block
+	typ := &b.Func.Config.Types
 	// match: (CondSelect x y bool)
 	// cond: flagArg(bool) == nil
-	// result: (ISEL [6] x y (CMPWconst [0] bool))
+	// result: (ISEL [6] x y (Select1 <types.TypeFlags> (ANDCCconst [1] bool)))
 	for {
 		x := v_0
 		y := v_1
@@ -1184,9 +1185,11 @@ func rewriteValuePPC64_OpCondSelect(v *Value) bool {
 		}
 		v.reset(OpPPC64ISEL)
 		v.AuxInt = int32ToAuxInt(6)
-		v0 := b.NewValue0(v.Pos, OpPPC64CMPWconst, types.TypeFlags)
-		v0.AuxInt = int32ToAuxInt(0)
-		v0.AddArg(bool)
+		v0 := b.NewValue0(v.Pos, OpSelect1, types.TypeFlags)
+		v1 := b.NewValue0(v.Pos, OpPPC64ANDCCconst, types.NewTuple(typ.Int, types.TypeFlags))
+		v1.AuxInt = int64ToAuxInt(1)
+		v1.AddArg(bool)
+		v0.AddArg(v1)
 		v.AddArg3(x, y, v0)
 		return true
 	}
@@ -5355,7 +5358,7 @@ func rewriteValuePPC64_OpPPC64ISEL(v *Value) bool {
 		v.AddArg(v0)
 		return true
 	}
-	// match: (ISEL [6] x y (CMPWconst [0] (ISELB [c] one cmp)))
+	// match: (ISEL [6] x y (Select1 (ANDCCconst [1] (ISELB [c] one cmp))))
 	// result: (ISEL [c] x y cmp)
 	for {
 		if auxIntToInt32(v.AuxInt) != 6 {
@@ -5363,15 +5366,19 @@ func rewriteValuePPC64_OpPPC64ISEL(v *Value) bool {
 		}
 		x := v_0
 		y := v_1
-		if v_2.Op != OpPPC64CMPWconst || auxIntToInt32(v_2.AuxInt) != 0 {
+		if v_2.Op != OpSelect1 {
 			break
 		}
 		v_2_0 := v_2.Args[0]
-		if v_2_0.Op != OpPPC64ISELB {
+		if v_2_0.Op != OpPPC64ANDCCconst || auxIntToInt64(v_2_0.AuxInt) != 1 {
 			break
 		}
-		c := auxIntToInt32(v_2_0.AuxInt)
-		cmp := v_2_0.Args[1]
+		v_2_0_0 := v_2_0.Args[0]
+		if v_2_0_0.Op != OpPPC64ISELB {
+			break
+		}
+		c := auxIntToInt32(v_2_0_0.AuxInt)
+		cmp := v_2_0_0.Args[1]
 		v.reset(OpPPC64ISEL)
 		v.AuxInt = int32ToAuxInt(c)
 		v.AddArg3(x, y, cmp)