cmd/asm: Fix encoding error of register offset shifted by 0 on arm64
The following instruction is wrongly encoded on arm64:
MOVD (R2)(R3<<0), R1
It's incorrectly encoded as
MOVD (R2)(R3<<3), R1
The reason for the error is that we hard-coded the shift encoding to 6,
which is correct for the MOVB and MOVBU instructions because it only
allows a shift amount of 0, but it is wrong for the MOVD instruction
because it also allows other shift values.
For instructions MOVB, MOVBU and FMOVB, the extension amount must be 0,
encoded in "S" as 0 if omitted, or as 1 if present. But in Go, we don't
distinguish between Rn.<EXT> and Rn.<EXT><<0, so we encode it as that
does not present. This makes no difference to the function of the
instruction.
Change-Id: I2afe3498392cc9b2ecd524c7744f28b9d6d107b8
Reviewed-on: https://go-review.googlesource.com/c/go/+/510995 Reviewed-by: Heschi Kreinick <heschi@google.com> Reviewed-by: Cherry Mui <cherryyz@google.com>
Run-TryBot: Eric Fang <eric.fang@arm.com>
TryBot-Result: Gopher Robot <gobot@golang.org>