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cmd/compile: elide sign-extend after zero-extend for wasm

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Add rules to eliminate sign-extension of values that have already
been zero-extended from fewer bits via an I64And mask:

  (I64Extend32S x:(I64And _ (I64Const [c]))) && c >= 0 && int64(int32(c)) == c => x
  (I64Extend16S x:(I64And _ (I64Const [c]))) && c >= 0 && int64(int16(c)) == c => x
  (I64Extend8S  x:(I64And _ (I64Const [c]))) && c >= 0 && int64(int8(c))  == c => x

When a value has been masked to fit within the non-negative range of
the sign-extension width, the upper bits are already zero and sign-
extending is a no-op. For example, (I64Extend32S (I64And x 0xff))
can be elided because 0xff fits in a signed int32, so bit 31 is
guaranteed to be zero and sign-extending from 32 bits is identity.

Cq-Include-Trybots: luci.golang.try:gotip-wasip1-wasm_wasmtime,gotip-wasip1-wasm_wazero
Change-Id: Ia54d67358756e47ca7635a6a8ca4beadb003820a
Reviewed-on: https://go-review.googlesource.com/c/go/+/756320
Reviewed-by: Keith Randall <khr@google.com>
Reviewed-by: Carlos Amedee <carlos@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Keith Randall <khr@golang.org>
Auto-Submit: Keith Randall <khr@golang.org>
This commit is contained in:
George Adams
2026-03-18 09:16:54 +00:00
committed by Gopher Robot
parent 686b127fe8
commit 55de3efde3
2 changed files with 67 additions and 0 deletions
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7
src/cmd/compile/internal/ssa/_gen/Wasm.rules
View File

@@ -412,6 +412,13 @@
(I64Extend32S (I64Extend8S x)) => (I64Extend8S x)
(I64Extend16S (I64Extend8S x)) => (I64Extend8S x)
// Sign-extend of a value already zero-extended from fewer bits is a no-op.
// E.g. (I64Extend32S (I64And x (I64Const [0xff]))) — top 33 bits are already
// zero, so sign-extending from 32 is identity.
(I64Extend32S x:(I64And _ (I64Const [c]))) && c >= 0 && int64(int32(c)) == c => x
(I64Extend16S x:(I64And _ (I64Const [c]))) && c >= 0 && int64(int16(c)) == c => x
(I64Extend8S x:(I64And _ (I64Const [c]))) && c >= 0 && int64(int8(c)) == c => x
// TODO: declare these operations as commutative and get rid of these rules?
(I64Add (I64Const [x]) y) && y.Op != OpWasmI64Const => (I64Add y (I64Const [x]))
(I64Mul (I64Const [x]) y) && y.Op != OpWasmI64Const => (I64Mul y (I64Const [x]))

60
src/cmd/compile/internal/ssa/rewriteWasm.go
View File

@@ -4135,6 +4135,26 @@ func rewriteValueWasm_OpWasmI64Extend16S(v *Value) bool {
v.AddArg(x)
return true
}
// match: (I64Extend16S x:(I64And _ (I64Const [c])))
// cond: c >= 0 && int64(int16(c)) == c
// result: x
for {
x := v_0
if x.Op != OpWasmI64And {
break
}
_ = x.Args[1]
x_1 := x.Args[1]
if x_1.Op != OpWasmI64Const {
break
}
c := auxIntToInt64(x_1.AuxInt)
if !(c >= 0 && int64(int16(c)) == c) {
break
}
v.copyOf(x)
return true
}
return false
}
func rewriteValueWasm_OpWasmI64Extend32S(v *Value) bool {
@@ -4172,6 +4192,26 @@ func rewriteValueWasm_OpWasmI64Extend32S(v *Value) bool {
v.AddArg(x)
return true
}
// match: (I64Extend32S x:(I64And _ (I64Const [c])))
// cond: c >= 0 && int64(int32(c)) == c
// result: x
for {
x := v_0
if x.Op != OpWasmI64And {
break
}
_ = x.Args[1]
x_1 := x.Args[1]
if x_1.Op != OpWasmI64Const {
break
}
c := auxIntToInt64(x_1.AuxInt)
if !(c >= 0 && int64(int32(c)) == c) {
break
}
v.copyOf(x)
return true
}
return false
}
func rewriteValueWasm_OpWasmI64Extend8S(v *Value) bool {
@@ -4187,6 +4227,26 @@ func rewriteValueWasm_OpWasmI64Extend8S(v *Value) bool {
v.AddArg(x)
return true
}
// match: (I64Extend8S x:(I64And _ (I64Const [c])))
// cond: c >= 0 && int64(int8(c)) == c
// result: x
for {
x := v_0
if x.Op != OpWasmI64And {
break
}
_ = x.Args[1]
x_1 := x.Args[1]
if x_1.Op != OpWasmI64Const {
break
}
c := auxIntToInt64(x_1.AuxInt)
if !(c >= 0 && int64(int8(c)) == c) {
break
}
v.copyOf(x)
return true
}
return false
}
func rewriteValueWasm_OpWasmI64LeU(v *Value) bool {