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>

0 files changed, 0 insertions, 0 deletions