cmd/compile: shift tests, fix triple-shift rules

Add a bunch of tests for shifts.

Fix triple-shift rules to always take constant shifts as 64 bits.
(Earlier rules always promote shift amounts to 64 bits.)
Add overflow checks.

Increases generic rule coverage to 91%

Change-Id: I6b42d368d19d36ac482dbb8e0d4f67e30ad7145d
Reviewed-on: https://go-review.googlesource.com/23555Reviewed-by: Todd Neal <todd@tneal.org>

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

@@ -246,17 +246,53 @@
 
 // zero shifted.
 (Lsh64x64  (Const64 [0]) _) -> (Const64 [0])
+(Lsh64x32  (Const64 [0]) _) -> (Const64 [0])
+(Lsh64x16  (Const64 [0]) _) -> (Const64 [0])
+(Lsh64x8  (Const64 [0]) _) -> (Const64 [0])
 (Rsh64x64  (Const64 [0]) _) -> (Const64 [0])
+(Rsh64x32  (Const64 [0]) _) -> (Const64 [0])
+(Rsh64x16  (Const64 [0]) _) -> (Const64 [0])
+(Rsh64x8  (Const64 [0]) _) -> (Const64 [0])
 (Rsh64Ux64 (Const64 [0]) _) -> (Const64 [0])
-(Lsh32x64  (Const64 [0]) _) -> (Const32 [0])
-(Rsh32x64  (Const64 [0]) _) -> (Const32 [0])
-(Rsh32Ux64 (Const64 [0]) _) -> (Const32 [0])
-(Lsh16x64  (Const64 [0]) _) -> (Const16 [0])
-(Rsh16x64  (Const64 [0]) _) -> (Const16 [0])
-(Rsh16Ux64 (Const64 [0]) _) -> (Const16 [0])
-(Lsh8x64   (Const64 [0]) _) -> (Const8  [0])
-(Rsh8x64   (Const64 [0]) _) -> (Const8  [0])
-(Rsh8Ux64  (Const64 [0]) _) -> (Const8  [0])
+(Rsh64Ux32 (Const64 [0]) _) -> (Const64 [0])
+(Rsh64Ux16 (Const64 [0]) _) -> (Const64 [0])
+(Rsh64Ux8 (Const64 [0]) _) -> (Const64 [0])
+(Lsh32x64  (Const32 [0]) _) -> (Const32 [0])
+(Lsh32x32  (Const32 [0]) _) -> (Const32 [0])
+(Lsh32x16  (Const32 [0]) _) -> (Const32 [0])
+(Lsh32x8  (Const32 [0]) _) -> (Const32 [0])
+(Rsh32x64  (Const32 [0]) _) -> (Const32 [0])
+(Rsh32x32  (Const32 [0]) _) -> (Const32 [0])
+(Rsh32x16  (Const32 [0]) _) -> (Const32 [0])
+(Rsh32x8  (Const32 [0]) _) -> (Const32 [0])
+(Rsh32Ux64 (Const32 [0]) _) -> (Const32 [0])
+(Rsh32Ux32 (Const32 [0]) _) -> (Const32 [0])
+(Rsh32Ux16 (Const32 [0]) _) -> (Const32 [0])
+(Rsh32Ux8 (Const32 [0]) _) -> (Const32 [0])
+(Lsh16x64  (Const16 [0]) _) -> (Const16 [0])
+(Lsh16x32  (Const16 [0]) _) -> (Const16 [0])
+(Lsh16x16  (Const16 [0]) _) -> (Const16 [0])
+(Lsh16x8  (Const16 [0]) _) -> (Const16 [0])
+(Rsh16x64  (Const16 [0]) _) -> (Const16 [0])
+(Rsh16x32  (Const16 [0]) _) -> (Const16 [0])
+(Rsh16x16  (Const16 [0]) _) -> (Const16 [0])
+(Rsh16x8  (Const16 [0]) _) -> (Const16 [0])
+(Rsh16Ux64 (Const16 [0]) _) -> (Const16 [0])
+(Rsh16Ux32 (Const16 [0]) _) -> (Const16 [0])
+(Rsh16Ux16 (Const16 [0]) _) -> (Const16 [0])
+(Rsh16Ux8 (Const16 [0]) _) -> (Const16 [0])
+(Lsh8x64   (Const8 [0]) _) -> (Const8  [0])
+(Lsh8x32   (Const8 [0]) _) -> (Const8  [0])
+(Lsh8x16   (Const8 [0]) _) -> (Const8  [0])
+(Lsh8x8   (Const8 [0]) _) -> (Const8  [0])
+(Rsh8x64   (Const8 [0]) _) -> (Const8  [0])
+(Rsh8x32   (Const8 [0]) _) -> (Const8  [0])
+(Rsh8x16   (Const8 [0]) _) -> (Const8  [0])
+(Rsh8x8   (Const8 [0]) _) -> (Const8  [0])
+(Rsh8Ux64  (Const8 [0]) _) -> (Const8  [0])
+(Rsh8Ux32  (Const8 [0]) _) -> (Const8  [0])
+(Rsh8Ux16  (Const8 [0]) _) -> (Const8  [0])
+(Rsh8Ux8  (Const8 [0]) _) -> (Const8  [0])
 
 // large left shifts of all values, and right shifts of unsigned values
 (Lsh64x64  _ (Const64 [c])) && uint64(c) >= 64 -> (Const64 [0])
@@ -286,31 +322,31 @@
 
 // ((x >> c1) << c2) >> c3
 (Rsh64Ux64 (Lsh64x64 (Rsh64Ux64 x (Const64 [c1])) (Const64 [c2])) (Const64 [c3]))
-  && uint64(c1) >= uint64(c2) && uint64(c3) >= uint64(c2)
+  && uint64(c1) >= uint64(c2) && uint64(c3) >= uint64(c2) && !uaddOvf(c1-c2, c3)
   -> (Rsh64Ux64 x (Const64 <config.fe.TypeUInt64()> [c1-c2+c3]))
-(Rsh32Ux64 (Lsh32x64 (Rsh32Ux64 x (Const32 [c1])) (Const32 [c2])) (Const32 [c3]))
-  && uint32(c1) >= uint32(c2) && uint32(c3) >= uint32(c2)
-  -> (Rsh32Ux64 x (Const32 <config.fe.TypeUInt32()> [int64(int32(c1-c2+c3))]))
-(Rsh16Ux64 (Lsh16x64 (Rsh16Ux64 x (Const16 [c1])) (Const16 [c2])) (Const16 [c3]))
-  && uint16(c1) >= uint16(c2) && uint16(c3) >= uint16(c2)
-  -> (Rsh16Ux64 x (Const16 <config.fe.TypeUInt16()> [int64(int16(c1-c2+c3))]))
-(Rsh8Ux64 (Lsh8x64 (Rsh8Ux64 x (Const8 [c1])) (Const8 [c2])) (Const8 [c3]))
-  && uint8(c1) >= uint8(c2) && uint8(c3) >= uint8(c2)
-  -> (Rsh8Ux64 x (Const8 <config.fe.TypeUInt8()> [int64(int8(c1-c2+c3))]))
+(Rsh32Ux64 (Lsh32x64 (Rsh32Ux64 x (Const64 [c1])) (Const64 [c2])) (Const64 [c3]))
+  && uint64(c1) >= uint64(c2) && uint64(c3) >= uint64(c2) && !uaddOvf(c1-c2, c3)
+  -> (Rsh32Ux64 x (Const64 <config.fe.TypeUInt64()> [c1-c2+c3]))
+(Rsh16Ux64 (Lsh16x64 (Rsh16Ux64 x (Const64 [c1])) (Const64 [c2])) (Const64 [c3]))
+  && uint64(c1) >= uint64(c2) && uint64(c3) >= uint64(c2) && !uaddOvf(c1-c2, c3)
+  -> (Rsh16Ux64 x (Const64 <config.fe.TypeUInt64()> [c1-c2+c3]))
+(Rsh8Ux64 (Lsh8x64 (Rsh8Ux64 x (Const64 [c1])) (Const64 [c2])) (Const64 [c3]))
+  && uint64(c1) >= uint64(c2) && uint64(c3) >= uint64(c2) && !uaddOvf(c1-c2, c3)
+  -> (Rsh8Ux64 x (Const64 <config.fe.TypeUInt64()> [c1-c2+c3]))
 
 // ((x << c1) >> c2) << c3
 (Lsh64x64 (Rsh64Ux64 (Lsh64x64 x (Const64 [c1])) (Const64 [c2])) (Const64 [c3]))
-  && uint64(c1) >= uint64(c2) && uint64(c3) >= uint64(c2)
+  && uint64(c1) >= uint64(c2) && uint64(c3) >= uint64(c2) && !uaddOvf(c1-c2, c3)
   -> (Lsh64x64 x (Const64 <config.fe.TypeUInt64()> [c1-c2+c3]))
-(Lsh32x64 (Rsh32Ux64 (Lsh32x64 x (Const32 [c1])) (Const32 [c2])) (Const32 [c3]))
-  && uint32(c1) >= uint32(c2) && uint32(c3) >= uint32(c2)
-  -> (Lsh32x64 x (Const32 <config.fe.TypeUInt32()> [int64(int32(c1-c2+c3))]))
-(Lsh16x64 (Rsh16Ux64 (Lsh16x64 x (Const16 [c1])) (Const16 [c2])) (Const16 [c3]))
-  && uint16(c1) >= uint16(c2) && uint16(c3) >= uint16(c2)
-  -> (Lsh16x64 x (Const16 <config.fe.TypeUInt16()> [int64(int16(c1-c2+c3))]))
-(Lsh8x64 (Rsh8Ux64 (Lsh8x64 x (Const8 [c1])) (Const8 [c2])) (Const8 [c3]))
-  && uint8(c1) >= uint8(c2) && uint8(c3) >= uint8(c2)
-  -> (Lsh8x64 x (Const8 <config.fe.TypeUInt8()> [int64(int8(c1-c2+c3))]))
+(Lsh32x64 (Rsh32Ux64 (Lsh32x64 x (Const64 [c1])) (Const64 [c2])) (Const64 [c3]))
+  && uint64(c1) >= uint64(c2) && uint64(c3) >= uint64(c2) && !uaddOvf(c1-c2, c3)
+  -> (Lsh32x64 x (Const64 <config.fe.TypeUInt64()> [c1-c2+c3]))
+(Lsh16x64 (Rsh16Ux64 (Lsh16x64 x (Const64 [c1])) (Const64 [c2])) (Const64 [c3]))
+  && uint64(c1) >= uint64(c2) && uint64(c3) >= uint64(c2) && !uaddOvf(c1-c2, c3)
+  -> (Lsh16x64 x (Const64 <config.fe.TypeUInt64()> [c1-c2+c3]))
+(Lsh8x64 (Rsh8Ux64 (Lsh8x64 x (Const64 [c1])) (Const64 [c2])) (Const64 [c3]))
+  && uint64(c1) >= uint64(c2) && uint64(c3) >= uint64(c2) && !uaddOvf(c1-c2, c3)
+  -> (Lsh8x64 x (Const64 <config.fe.TypeUInt64()> [c1-c2+c3]))
 
 // constant comparisons
 (Eq64 (Const64 [c]) (Const64 [d])) -> (ConstBool [b2i(c == d)])