cmd/compile: stop MOVW-ing -1 as SRA shift amount in mips

The shift amount in SRAconst needs to be in the [0,31] range, so stop
MOVWing -1 to SRA in the Rsh lowering rules.

Also see CL 270117.

Passes

  $ GOARCH=mips go build -toolexec 'toolstash -cmp' -a std
  $ GOARCH=mipsle go build -toolexec 'toolstash -cmp' -a std

Updates #42587

Change-Id: Ib5eb99b82310e404cc2d6f0c619b21b8a15406ce
Reviewed-on: https://go-review.googlesource.com/c/go/+/270558
Trust: Alberto Donizetti <[email protected]>
Run-TryBot: Alberto Donizetti <[email protected]>
TryBot-Result: Go Bot <[email protected]>
Reviewed-by: Cherry Zhang <[email protected]>

Author: ALTree

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

@@ -96,17 +96,17 @@
 (Rsh8Ux16 <t> x y) => (CMOVZ (SRL <t> (ZeroExt8to32 x) (ZeroExt16to32 y) ) (MOVWconst [0]) (SGTUconst [32] (ZeroExt16to32 y)))
 (Rsh8Ux8 <t> x y)  => (CMOVZ (SRL <t> (ZeroExt8to32 x) (ZeroExt8to32 y) ) (MOVWconst [0]) (SGTUconst [32] (ZeroExt8to32 y)))
 
-(Rsh32x32 x y) => (SRA x ( CMOVZ <typ.UInt32> y (MOVWconst [-1]) (SGTUconst [32] y)))
-(Rsh32x16 x y) => (SRA x ( CMOVZ <typ.UInt32> (ZeroExt16to32 y) (MOVWconst [-1]) (SGTUconst [32] (ZeroExt16to32 y))))
-(Rsh32x8 x y)  => (SRA x ( CMOVZ <typ.UInt32> (ZeroExt8to32 y) (MOVWconst [-1]) (SGTUconst [32] (ZeroExt8to32 y))))
+(Rsh32x32 x y) => (SRA x ( CMOVZ <typ.UInt32> y (MOVWconst [31]) (SGTUconst [32] y)))
+(Rsh32x16 x y) => (SRA x ( CMOVZ <typ.UInt32> (ZeroExt16to32 y) (MOVWconst [31]) (SGTUconst [32] (ZeroExt16to32 y))))
+(Rsh32x8 x y)  => (SRA x ( CMOVZ <typ.UInt32> (ZeroExt8to32 y) (MOVWconst [31]) (SGTUconst [32] (ZeroExt8to32 y))))
 
-(Rsh16x32 x y) => (SRA (SignExt16to32 x) ( CMOVZ <typ.UInt32> y (MOVWconst [-1]) (SGTUconst [32] y)))
-(Rsh16x16 x y) => (SRA (SignExt16to32 x) ( CMOVZ <typ.UInt32> (ZeroExt16to32 y) (MOVWconst [-1]) (SGTUconst [32] (ZeroExt16to32 y))))
-(Rsh16x8 x y)  => (SRA (SignExt16to32 x) ( CMOVZ <typ.UInt32> (ZeroExt8to32 y) (MOVWconst [-1]) (SGTUconst [32] (ZeroExt8to32 y))))
+(Rsh16x32 x y) => (SRA (SignExt16to32 x) ( CMOVZ <typ.UInt32> y (MOVWconst [31]) (SGTUconst [32] y)))
+(Rsh16x16 x y) => (SRA (SignExt16to32 x) ( CMOVZ <typ.UInt32> (ZeroExt16to32 y) (MOVWconst [31]) (SGTUconst [32] (ZeroExt16to32 y))))
+(Rsh16x8 x y)  => (SRA (SignExt16to32 x) ( CMOVZ <typ.UInt32> (ZeroExt8to32 y) (MOVWconst [31]) (SGTUconst [32] (ZeroExt8to32 y))))
 
-(Rsh8x32 x y) => (SRA (SignExt16to32 x) ( CMOVZ <typ.UInt32> y (MOVWconst [-1]) (SGTUconst [32] y)))
-(Rsh8x16 x y) => (SRA (SignExt16to32 x) ( CMOVZ <typ.UInt32> (ZeroExt16to32 y) (MOVWconst [-1]) (SGTUconst [32] (ZeroExt16to32 y))))
-(Rsh8x8 x y)  => (SRA (SignExt16to32 x) ( CMOVZ <typ.UInt32> (ZeroExt8to32 y) (MOVWconst [-1]) (SGTUconst [32] (ZeroExt8to32 y))))
+(Rsh8x32 x y) => (SRA (SignExt16to32 x) ( CMOVZ <typ.UInt32> y (MOVWconst [31]) (SGTUconst [32] y)))
+(Rsh8x16 x y) => (SRA (SignExt16to32 x) ( CMOVZ <typ.UInt32> (ZeroExt16to32 y) (MOVWconst [31]) (SGTUconst [32] (ZeroExt16to32 y))))
+(Rsh8x8 x y)  => (SRA (SignExt16to32 x) ( CMOVZ <typ.UInt32> (ZeroExt8to32 y) (MOVWconst [31]) (SGTUconst [32] (ZeroExt8to32 y))))
 
 // rotates
 (RotateLeft8  <t> x (MOVWconst [c])) => (Or8  (Lsh8x32 <t>  x (MOVWconst [c&7]))  (Rsh8Ux32 <t> x (MOVWconst [-c&7])))