cmd/compile: add identity and absorption rules for wasm

Add post-lowering identity and absorption rules for I64And, I64Or,
I64Xor, and I64Mul with constant operands:

  (I64And x (I64Const [-1])) => x
  (I64And x (I64Const [0])) => (I64Const [0])
  (I64Or  x (I64Const [0])) => x
  (I64Or  x (I64Const [-1])) => (I64Const [-1])
  (I64Xor x (I64Const [0])) => x
  (I64Mul x (I64Const [0])) => (I64Const [0])
  (I64Mul x (I64Const [1])) => x

The generic SSA rules handle these patterns before lowering, but
these rules catch cases where wasm-specific lowering or other
post-lowering optimization passes produce new nodes with identity
or absorbing constant operands.

For example, the complement rule lowers Com64(x) to
(I64Xor x (I64Const [-1])), and if x is later determined to be
all-ones, the I64And absorption rule can fold the result to zero.

Cq-Include-Trybots: luci.golang.try:gotip-wasip1-wasm_wasmtime,gotip-wasip1-wasm_wazero
Change-Id: Ie9a40e075662d4828a70e30b258d92ee171d0bc2
Reviewed-on: https://go-review.googlesource.com/c/go/+/752861
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Keith Randall <khr@golang.org>
Reviewed-by: Keith Randall <khr@google.com>
Reviewed-by: Keith Randall <khr@golang.org>
Reviewed-by: David Chase <drchase@google.com>

2 files changed, 80 insertions, 0 deletions

diff --git a/src/cmd/compile/internal/ssa/_gen/Wasm.rules b/src/cmd/compile/internal/ssa/_gen/Wasm.rules
index 8490fb39b8..9b582c8c00 100644
--- a/src/cmd/compile/internal/ssa/_gen/Wasm.rules
+++ b/src/cmd/compile/internal/ssa/_gen/Wasm.rules
@@ -390,6 +390,16 @@
 (I64ShrU (I64Const [x]) (I64Const [y])) => (I64Const [int64(uint64(x) >> uint64(y))])
 (I64ShrS (I64Const [x]) (I64Const [y])) => (I64Const [x >> uint64(y)])
 
+// Identity and absorption rules for AND/OR/XOR/MUL.
+// These fire on nodes created during or after lowering.
+(I64And x (I64Const [-1])) => x
+(I64And x (I64Const [0])) => (I64Const [0])
+(I64Or  x (I64Const [0])) => x
+(I64Or  x (I64Const [-1])) => (I64Const [-1])
+(I64Xor x (I64Const [0])) => x
+(I64Mul x (I64Const [0])) => (I64Const [0])
+(I64Mul x (I64Const [1])) => 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]))
diff --git a/src/cmd/compile/internal/ssa/rewriteWasm.go b/src/cmd/compile/internal/ssa/rewriteWasm.go
index 68a40f0c7f..c0ccd9611d 100644
--- a/src/cmd/compile/internal/ssa/rewriteWasm.go
+++ b/src/cmd/compile/internal/ssa/rewriteWasm.go
@@ -3949,6 +3949,26 @@ func rewriteValueWasm_OpWasmI64And(v *Value) bool {
 		v.AuxInt = int64ToAuxInt(x & y)
 		return true
 	}
+	// match: (I64And x (I64Const [-1]))
+	// result: x
+	for {
+		x := v_0
+		if v_1.Op != OpWasmI64Const || auxIntToInt64(v_1.AuxInt) != -1 {
+			break
+		}
+		v.copyOf(x)
+		return true
+	}
+	// match: (I64And x (I64Const [0]))
+	// result: (I64Const [0])
+	for {
+		if v_1.Op != OpWasmI64Const || auxIntToInt64(v_1.AuxInt) != 0 {
+			break
+		}
+		v.reset(OpWasmI64Const)
+		v.AuxInt = int64ToAuxInt(0)
+		return true
+	}
 	// match: (I64And (I64Const [x]) y)
 	// cond: y.Op != OpWasmI64Const
 	// result: (I64And y (I64Const [x]))
@@ -4448,6 +4468,26 @@ func rewriteValueWasm_OpWasmI64Mul(v *Value) bool {
 		v.AuxInt = int64ToAuxInt(x * y)
 		return true
 	}
+	// match: (I64Mul x (I64Const [0]))
+	// result: (I64Const [0])
+	for {
+		if v_1.Op != OpWasmI64Const || auxIntToInt64(v_1.AuxInt) != 0 {
+			break
+		}
+		v.reset(OpWasmI64Const)
+		v.AuxInt = int64ToAuxInt(0)
+		return true
+	}
+	// match: (I64Mul x (I64Const [1]))
+	// result: x
+	for {
+		x := v_0
+		if v_1.Op != OpWasmI64Const || auxIntToInt64(v_1.AuxInt) != 1 {
+			break
+		}
+		v.copyOf(x)
+		return true
+	}
 	// match: (I64Mul (I64Const [x]) y)
 	// cond: y.Op != OpWasmI64Const
 	// result: (I64Mul y (I64Const [x]))
@@ -4564,6 +4604,26 @@ func rewriteValueWasm_OpWasmI64Or(v *Value) bool {
 		v.AuxInt = int64ToAuxInt(x | y)
 		return true
 	}
+	// match: (I64Or x (I64Const [0]))
+	// result: x
+	for {
+		x := v_0
+		if v_1.Op != OpWasmI64Const || auxIntToInt64(v_1.AuxInt) != 0 {
+			break
+		}
+		v.copyOf(x)
+		return true
+	}
+	// match: (I64Or x (I64Const [-1]))
+	// result: (I64Const [-1])
+	for {
+		if v_1.Op != OpWasmI64Const || auxIntToInt64(v_1.AuxInt) != -1 {
+			break
+		}
+		v.reset(OpWasmI64Const)
+		v.AuxInt = int64ToAuxInt(-1)
+		return true
+	}
 	// match: (I64Or (I64Const [x]) y)
 	// cond: y.Op != OpWasmI64Const
 	// result: (I64Or y (I64Const [x]))
@@ -4788,6 +4848,16 @@ func rewriteValueWasm_OpWasmI64Xor(v *Value) bool {
 		v.AuxInt = int64ToAuxInt(x ^ y)
 		return true
 	}
+	// match: (I64Xor x (I64Const [0]))
+	// result: x
+	for {
+		x := v_0
+		if v_1.Op != OpWasmI64Const || auxIntToInt64(v_1.AuxInt) != 0 {
+			break
+		}
+		v.copyOf(x)
+		return true
+	}
 	// match: (I64Xor (I64Const [x]) y)
 	// cond: y.Op != OpWasmI64Const
 	// result: (I64Xor y (I64Const [x]))