cmd/compile: add rules handling unsigned div/mod by constant 1<<63

Normally 64-bit div/mod is turned into runtime calls on 32-bit
arch, but the front end leaves power-of-two constant division
and hopes the SSA backend turns into a shift or AND. The SSA rule is

(Mod64u <t> n (Const64 [c])) && isPowerOfTwo(c) -> (And64 n (Const64 <t> [c-1]))

But isPowerOfTwo returns true only for positive int64, which leaves
out 1<<63 unhandled. Add a special case for 1<<63.

Fixes #21517.

Change-Id: I02d27dc7177d4af0ee8d7f5533714edecddf8c95
Reviewed-on: https://go-review.googlesource.com/56890Reviewed-by: Keith Randall <khr@golang.org>

src/cmd/compile/internal/gc/testdata/gen/arithConstGen.go

@@ -31,7 +31,7 @@ type szD struct {
 }
 
 var szs = []szD{
-	{name: "uint64", sn: "64", u: []uint64{0, 1, 4294967296, 0xffffFFFFffffFFFF}},
+	{name: "uint64", sn: "64", u: []uint64{0, 1, 4294967296, 0x8000000000000000, 0xffffFFFFffffFFFF}},
 	{name: "int64", sn: "64", i: []int64{-0x8000000000000000, -0x7FFFFFFFFFFFFFFF,
 		-4294967296, -1, 0, 1, 4294967296, 0x7FFFFFFFFFFFFFFE, 0x7FFFFFFFFFFFFFFF}},
 

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

@@ -962,6 +962,7 @@
 (Div16u n (Const16 [c])) && isPowerOfTwo(c&0xffff)     -> (Rsh16Ux64 n (Const64 <typ.UInt64> [log2(c&0xffff)]))
 (Div32u n (Const32 [c])) && isPowerOfTwo(c&0xffffffff) -> (Rsh32Ux64 n (Const64 <typ.UInt64> [log2(c&0xffffffff)]))
 (Div64u n (Const64 [c])) && isPowerOfTwo(c)            -> (Rsh64Ux64 n (Const64 <typ.UInt64> [log2(c)]))
+(Div64u n (Const64 [-1<<63]))                          -> (Rsh64Ux64 n (Const64 <typ.UInt64> [63]))
 
 // Unsigned divide, not a power of 2.  Strength reduce to a multiply.
 // For 8-bit divides, we just do a direct 9-bit by 8-bit multiply.
@@ -1194,6 +1195,7 @@
 (Mod16u <t> n (Const16 [c])) && isPowerOfTwo(c&0xffff)     -> (And16 n (Const16 <t> [(c&0xffff)-1]))
 (Mod32u <t> n (Const32 [c])) && isPowerOfTwo(c&0xffffffff) -> (And32 n (Const32 <t> [(c&0xffffffff)-1]))
 (Mod64u <t> n (Const64 [c])) && isPowerOfTwo(c)            -> (And64 n (Const64 <t> [c-1]))
+(Mod64u <t> n (Const64 [-1<<63]))                          -> (And64 n (Const64 <t> [1<<63-1]))
 
 // Signed mod by negative constant.
 (Mod8  <t> n (Const8  [c])) && c < 0 && c != -1<<7  -> (Mod8  <t> n (Const8  <t> [-c]))

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

@@ -8220,6 +8220,26 @@ func rewriteValuegeneric_OpDiv64u_0(v *Value) bool {
 		v.AddArg(v0)
 		return true
 	}
+	// match: (Div64u n (Const64 [-1<<63]))
+	// cond:
+	// result: (Rsh64Ux64 n (Const64 <typ.UInt64> [63]))
+	for {
+		_ = v.Args[1]
+		n := v.Args[0]
+		v_1 := v.Args[1]
+		if v_1.Op != OpConst64 {
+			break
+		}
+		if v_1.AuxInt != -1<<63 {
+			break
+		}
+		v.reset(OpRsh64Ux64)
+		v.AddArg(n)
+		v0 := b.NewValue0(v.Pos, OpConst64, typ.UInt64)
+		v0.AuxInt = 63
+		v.AddArg(v0)
+		return true
+	}
 	// match: (Div64u x (Const64 [c]))
 	// cond: umagicOK(64, c) && config.RegSize == 8 && umagic(64,c).m&1 == 0
 	// result: (Rsh64Ux64 <typ.UInt64>     (Hmul64u <typ.UInt64>       (Const64 <typ.UInt64> [int64(1<<63+umagic(64,c).m/2)])       x)     (Const64 <typ.UInt64> [umagic(64,c).s-1]))
@@ -13338,6 +13358,27 @@ func rewriteValuegeneric_OpMod64u_0(v *Value) bool {
 		v.AddArg(v0)
 		return true
 	}
+	// match: (Mod64u <t> n (Const64 [-1<<63]))
+	// cond:
+	// result: (And64 n (Const64 <t> [1<<63-1]))
+	for {
+		t := v.Type
+		_ = v.Args[1]
+		n := v.Args[0]
+		v_1 := v.Args[1]
+		if v_1.Op != OpConst64 {
+			break
+		}
+		if v_1.AuxInt != -1<<63 {
+			break
+		}
+		v.reset(OpAnd64)
+		v.AddArg(n)
+		v0 := b.NewValue0(v.Pos, OpConst64, t)
+		v0.AuxInt = 1<<63 - 1
+		v.AddArg(v0)
+		return true
+	}
 	// match: (Mod64u <t> x (Const64 [c]))
 	// cond: x.Op != OpConst64 && c > 0 && umagicOK(64,c)
 	// result: (Sub64 x (Mul64 <t> (Div64u <t> x (Const64 <t> [c])) (Const64 <t> [c])))