cmd/compile: optimize bounded shifts on wasm

Use the shiftIsBounded function to generate more efficient Shift instructions. Updates #25167 Change-Id: Id350f8462dc3a7ed3bfed0bcbea2860b8f40048a Reviewed-on: https://go-review.googlesource.com/c/go/+/182558 Run-TryBot: Agniva De Sarker <[email protected]> TryBot-Result: Gobot Gobot <[email protected]> Reviewed-by: Cherry Zhang <[email protected]> Reviewed-by: Richard Musiol <[email protected]>
golang · Aug 28, 2019 · 8fedb2d · 8fedb2d
1 parent b9ef4c0
commit 8fedb2d
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Showing 3 changed files with 50 additions and 5 deletions.
diff --git a/src/cmd/compile/internal/ssa/gen/Wasm.rules b/src/cmd/compile/internal/ssa/gen/Wasm.rules
@@ -102,6 +102,7 @@
 // Lowering shifts
 // Unsigned shifts need to return 0 if shift amount is >= width of shifted value.
 
+(Lsh64x64 x y) && shiftIsBounded(v) -> (I64Shl x y)
 (Lsh64x64 x y) -> (Select (I64Shl x y) (I64Const [0]) (I64LtU y (I64Const [64])))
 (Lsh64x(32|16|8) x y) -> (Lsh64x64 x (ZeroExt(32|16|8)to64 y))
 
@@ -114,6 +115,7 @@
 (Lsh8x64  x y) -> (Lsh64x64 x y)
 (Lsh8x(32|16|8)  x y) -> (Lsh64x64 x (ZeroExt(32|16|8)to64 y))
 
+(Rsh64Ux64 x y) && shiftIsBounded(v) -> (I64ShrU x y)
 (Rsh64Ux64 x y) -> (Select (I64ShrU x y) (I64Const [0]) (I64LtU y (I64Const [64])))
 (Rsh64Ux(32|16|8) x y) -> (Rsh64Ux64 x (ZeroExt(32|16|8)to64 y))
 
@@ -129,6 +131,7 @@
 // Signed right shift needs to return 0/-1 if shift amount is >= width of shifted value.
 // We implement this by setting the shift value to (width - 1) if the shift value is >= width.
 
+(Rsh64x64 x y) && shiftIsBounded(v) -> (I64ShrS x y)
 (Rsh64x64 x y) -> (I64ShrS x (Select <typ.Int64> y (I64Const [63]) (I64LtU y (I64Const [64]))))
 (Rsh64x(32|16|8) x y) -> (Rsh64x64 x (ZeroExt(32|16|8)to64 y))
 

diff --git a/src/cmd/compile/internal/ssa/rewriteWasm.go b/src/cmd/compile/internal/ssa/rewriteWasm.go
diff --git a/test/codegen/shift.go b/test/codegen/shift.go
@@ -102,25 +102,25 @@ func lshSignedMasked(v8 int8, v16 int16, v32 int32, v64 int64, x int) {
 //   bounded shifts   //
 // ------------------ //
 
-func lshGuarded64(v int64, s uint) int64 {
+func rshGuarded64(v int64, s uint) int64 {
 	if s < 64 {
-		// s390x:-".*AND",-".*MOVDGE"
+		// s390x:-".*AND",-".*MOVDGE" wasm:-"Select",-".*LtU"
 		return v >> s
 	}
 	panic("shift too large")
 }
 
 func rshGuarded64U(v uint64, s uint) uint64 {
 	if s < 64 {
-		// s390x:-".*AND",-".*MOVDGE"
+		// s390x:-".*AND",-".*MOVDGE" wasm:-"Select",-".*LtU"
 		return v >> s
 	}
 	panic("shift too large")
 }
 
-func rshGuarded64(v int64, s uint) int64 {
+func lshGuarded64(v int64, s uint) int64 {
 	if s < 64 {
-		// s390x:-".*AND",-".*MOVDGE"
+		// s390x:-".*AND",-".*MOVDGE" wasm:-"Select",-".*LtU"
 		return v << s
 	}
 	panic("shift too large")