This patch adds support for the `Operand2_R_LSL_I` addressing mode to
loads and stores. This allows merging a shift instruction into a
MemoryOperand. Since the shift immediate is restricted to the log2 of
the operation width, the opportunities to hit this are slim. However,
Ignition's bytecode handlers hit this case all the time:
kind = BYTECODE_HANDLER
name = Star
compiler = turbofan
Instructions (size = 44)
0x23e67280 0 add x1, x19, #0x1 (1)
0x23e67284 4 ldrsb x1, [x20, x1]
0x23e67288 8 sxtw x1, w1
0x23e6728c 12 mov x2, fp
0x23e67290 16 str x0, [x2, x1, lsl #3]
^^^^^^^^^^^^^^^^^^^^^
0x23e67294 20 add x19, x19, #0x2 (2)
0x23e67298 24 ldrb w1, [x20, x19]
0x23e6729c 28 ldr x1, [x21, x1, lsl #3]
^^^^^^^^^^^^^^^^^^^^^
0x23e672a0 32 br x1
Additionally, I noticed the optimisation occurs once in both the
`StringPrototypeCharAt` and `StringPrototypeCharCodeAt` turbofan stubs.
BUG=
Review-Url: https://codereview.chromium.org/1972103002
Cr-Commit-Position: refs/heads/master@{#36227}
60fb6ea1b8