cmd/compile: Fix constant-folding of unsigned shifts

Make sure the results of unsigned constant-folded
shifts are sign-extended into the AuxInt field.

Fixes #15175

Change-Id: I3490d1bc3d9b2e1578ed30964645508577894f58
Reviewed-on: https://go-review.googlesource.com/21586Reviewed-by: Alexandru Moșoi <alexandru@mosoi.ro>
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

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

@@ -81,13 +81,13 @@
 (Rsh64Ux64 (Const64 [c]) (Const64 [d])) -> (Const64 [int64(uint64(c) >> uint64(d))])
 (Lsh32x64  (Const32 [c]) (Const64 [d])) -> (Const32 [int64(int32(c) << uint64(d))])
 (Rsh32x64  (Const32 [c]) (Const64 [d])) -> (Const32 [int64(int32(c) >> uint64(d))])
-(Rsh32Ux64 (Const32 [c]) (Const64 [d])) -> (Const32 [int64(uint32(c) >> uint64(d))])
+(Rsh32Ux64 (Const32 [c]) (Const64 [d])) -> (Const32 [int64(int32(uint32(c) >> uint64(d)))])
 (Lsh16x64  (Const16 [c]) (Const64 [d])) -> (Const16 [int64(int16(c) << uint64(d))])
 (Rsh16x64  (Const16 [c]) (Const64 [d])) -> (Const16 [int64(int16(c) >> uint64(d))])
-(Rsh16Ux64 (Const16 [c]) (Const64 [d])) -> (Const16 [int64(uint16(c) >> uint64(d))])
+(Rsh16Ux64 (Const16 [c]) (Const64 [d])) -> (Const16 [int64(int16(uint16(c) >> uint64(d)))])
 (Lsh8x64   (Const8  [c]) (Const64 [d])) -> (Const8  [int64(int8(c) << uint64(d))])
 (Rsh8x64   (Const8  [c]) (Const64 [d])) -> (Const8  [int64(int8(c) >> uint64(d))])
-(Rsh8Ux64  (Const8  [c]) (Const64 [d])) -> (Const8  [int64(uint8(c) >> uint64(d))])
+(Rsh8Ux64  (Const8  [c]) (Const64 [d])) -> (Const8  [int64(int8(uint8(c) >> uint64(d)))])
 
 (Lsh64x64  (Const64 [0]) _) -> (Const64 [0])
 (Rsh64x64  (Const64 [0]) _) -> (Const64 [0])

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

@@ -6185,7 +6185,7 @@ func rewriteValuegeneric_OpRsh16Ux64(v *Value, config *Config) bool {
 	_ = b
 	// match: (Rsh16Ux64 (Const16 [c]) (Const64 [d]))
 	// cond:
-	// result: (Const16 [int64(uint16(c) >> uint64(d))])
+	// result: (Const16 [int64(int16(uint16(c) >> uint64(d)))])
 	for {
 		v_0 := v.Args[0]
 		if v_0.Op != OpConst16 {
@@ -6198,7 +6198,7 @@ func rewriteValuegeneric_OpRsh16Ux64(v *Value, config *Config) bool {
 		}
 		d := v_1.AuxInt
 		v.reset(OpConst16)
-		v.AuxInt = int64(uint16(c) >> uint64(d))
+		v.AuxInt = int64(int16(uint16(c) >> uint64(d)))
 		return true
 	}
 	// match: (Rsh16Ux64 (Const16 [0]) _)
@@ -6547,7 +6547,7 @@ func rewriteValuegeneric_OpRsh32Ux64(v *Value, config *Config) bool {
 	_ = b
 	// match: (Rsh32Ux64 (Const32 [c]) (Const64 [d]))
 	// cond:
-	// result: (Const32 [int64(uint32(c) >> uint64(d))])
+	// result: (Const32 [int64(int32(uint32(c) >> uint64(d)))])
 	for {
 		v_0 := v.Args[0]
 		if v_0.Op != OpConst32 {
@@ -6560,7 +6560,7 @@ func rewriteValuegeneric_OpRsh32Ux64(v *Value, config *Config) bool {
 		}
 		d := v_1.AuxInt
 		v.reset(OpConst32)
-		v.AuxInt = int64(uint32(c) >> uint64(d))
+		v.AuxInt = int64(int32(uint32(c) >> uint64(d)))
 		return true
 	}
 	// match: (Rsh32Ux64 (Const32 [0]) _)
@@ -7353,7 +7353,7 @@ func rewriteValuegeneric_OpRsh8Ux64(v *Value, config *Config) bool {
 	_ = b
 	// match: (Rsh8Ux64  (Const8  [c]) (Const64 [d]))
 	// cond:
-	// result: (Const8  [int64(uint8(c) >> uint64(d))])
+	// result: (Const8  [int64(int8(uint8(c) >> uint64(d)))])
 	for {
 		v_0 := v.Args[0]
 		if v_0.Op != OpConst8 {
@@ -7366,7 +7366,7 @@ func rewriteValuegeneric_OpRsh8Ux64(v *Value, config *Config) bool {
 		}
 		d := v_1.AuxInt
 		v.reset(OpConst8)
-		v.AuxInt = int64(uint8(c) >> uint64(d))
+		v.AuxInt = int64(int8(uint8(c) >> uint64(d)))
 		return true
 	}
 	// match: (Rsh8Ux64  (Const8  [0]) _)

test/fixedbugs/issue15175.go

+// run
+
+// Copyright 2016 The Go Authors.  All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Make sure unsigned shift results get sign-extended correctly.
+package main
+
+import "fmt"
+
+func main() {
+	failed := false
+	a6 := uint8(253)
+	if got := a6 >> 0; got != 253 {
+		fmt.Printf("uint8(253)>>0 = %v, wanted 253\n", got)
+		failed = true
+	}
+	if got := f1(0, 2, 1, 0, 0, 1, true); got != 255 {
+		fmt.Printf("f1(...) = %v, wanted 255\n", got)
+		failed = true
+	}
+	if got := f2(1); got != 242 {
+		fmt.Printf("f2(...) = %v, wanted 242\n", got)
+		failed = true
+	}
+	if got := f3(false, 0, 0); got != 254 {
+		fmt.Printf("f3(...) = %v, wanted 254\n", got)
+		failed = true
+	}
+	if failed {
+		panic("bad")
+	}
+}
+
+func f1(a1 uint, a2 int8, a3 int8, a4 int8, a5 uint8, a6 int, a7 bool) uint8 {
+	a5--
+	a4 += (a2 << a1 << 2) | (a4 ^ a4<<(a1&a1)) - a3                              // int8
+	a6 -= a6 >> (2 + uint32(a2)>>3)                                              // int
+	a1 += a1                                                                     // uint
+	a3 *= a4 << (a1 | a1) << (uint16(3) >> 2 & (1 - 0) & (uint16(1) << a5 << 3)) // int8
+	a7 = a7 || ((a2 == a4) || (a7 && a7) || ((a5 == a5) || (a7 || a7)))          // bool
+	return a5 >> a1
+}
+
+func f2(a1 uint8) uint8 {
+	a1--
+	a1--
+	a1 -= a1 + (a1 << 1) - (a1*a1*a1)<<(2-0+(3|3)-1)                // uint8
+	v1 := 0 * ((2 * 1) ^ 1) & ((uint(0) >> a1) + (2+0)*(uint(2)+0)) // uint
+	_ = v1
+	return a1 >> (((2 ^ 2) >> (v1 | 2)) + 0)
+}
+
+func f3(a1 bool, a2 uint, a3 int64) uint8 {
+	a3--
+	v1 := 1 & (2 & 1 * (1 ^ 2) & (uint8(3*1) >> 0)) // uint8
+	_ = v1
+	v1 += v1 - (v1 >> a2) + (v1 << (a2 ^ a2) & v1) // uint8
+	v1 *= v1                                       // uint8
+	a3--
+	v1 += v1 & v1 // uint8
+	v1--
+	v1 = ((v1 << 0) | v1>>0) + v1 // uint8
+	return v1 >> 0
+}