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cmd/compile: optimize bounded shifts on wasm

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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 <agniva.quicksilver@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
Reviewed-by: Richard Musiol <neelance@gmail.com>
This commit is contained in:
Agniva De Sarker 2019-06-16 16:07:55 +05:30 • committed by Agniva De Sarker
parent b9ef4c0f56
commit 8fedb2d338
3 changed files with 50 additions and 5 deletions
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3
src/cmd/compile/internal/ssa/gen/Wasm.rules
View file

@ -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))

42
src/cmd/compile/internal/ssa/rewriteWasm.go
View file

@ -2729,6 +2729,20 @@ func rewriteValueWasm_OpLsh64x64_0(v *Value) bool {
b := v.Block
typ := &b.Func.Config.Types
// match: (Lsh64x64 x y)
// cond: shiftIsBounded(v)
// result: (I64Shl x y)
for {
y := v.Args[1]
x := v.Args[0]
if !(shiftIsBounded(v)) {
break
}
v.reset(OpWasmI64Shl)
v.AddArg(x)
v.AddArg(y)
return true
}
// match: (Lsh64x64 x y)
// cond:
// result: (Select (I64Shl x y) (I64Const [0]) (I64LtU y (I64Const [64])))
for {
@ -4256,6 +4270,20 @@ func rewriteValueWasm_OpRsh64Ux64_0(v *Value) bool {
b := v.Block
typ := &b.Func.Config.Types
// match: (Rsh64Ux64 x y)
// cond: shiftIsBounded(v)
// result: (I64ShrU x y)
for {
y := v.Args[1]
x := v.Args[0]
if !(shiftIsBounded(v)) {
break
}
v.reset(OpWasmI64ShrU)
v.AddArg(x)
v.AddArg(y)
return true
}
// match: (Rsh64Ux64 x y)
// cond:
// result: (Select (I64ShrU x y) (I64Const [0]) (I64LtU y (I64Const [64])))
for {
@ -4333,6 +4361,20 @@ func rewriteValueWasm_OpRsh64x64_0(v *Value) bool {
b := v.Block
typ := &b.Func.Config.Types
// match: (Rsh64x64 x y)
// cond: shiftIsBounded(v)
// result: (I64ShrS x y)
for {
y := v.Args[1]
x := v.Args[0]
if !(shiftIsBounded(v)) {
break
}
v.reset(OpWasmI64ShrS)
v.AddArg(x)
v.AddArg(y)
return true
}
// match: (Rsh64x64 x y)
// cond:
// result: (I64ShrS x (Select <typ.Int64> y (I64Const [63]) (I64LtU y (I64Const [64]))))
for {

10
test/codegen/shift.go
View file

@ -102,9 +102,9 @@ 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")
@ -112,15 +112,15 @@ func lshGuarded64(v int64, s uint) int64 {
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")