Re: [PATCH][AArch64] Restrict MOV alias for ORR instruction

["Richard Earnshaw (lists)" <Richard dot Earnshaw at arm dot com>]

After some internal discussions we've agreed that your proposed patch is
probably the best solution here: namely that ORR should be used whenever
the shift is not "lsl #0".  So I've committed your patch with some minor
tweaks to the ChangeLog to make it more conformant with the house style.

Thanks for posting this, and sorry for taking so long to get a final answer.

R.

On 30/10/2018 18:12, Egeyar Bagcioglu wrote:
> Hello,
> 
> ARM Architecture Reference Manual for the profile ARMv8-A, Issue C.a,
> states that MOV (register) is an alias of the ORR (shifted register) iff
> shift == '00' && imm6 == '000000' && Rn == '11111'. However, mov is
> currently preferred for a broader range of orr instructions.
> 
> PR 23193 is filed for this purpose and still open. Another related one,
> 19721 was filed earlier and resolved inconsistently with the manual.
> 
> The attached patch fixes the opcodes to match the manual in this regard,
> corrects existing test cases and adds new ones. I have re-used the test
> source and the driver of the older pr, 19721.
> 
> I did *not* replace the existing Rm_SFT used in the "mov" entry with an
> Rm. Therefore, "mov" usages with shifted registers such as "mov x7, x17,
> lsl 25" could continue to be accepted. However, they are not generated
> anymore.
> 
> 
> The suggested change log is the following:
> 
> 2018-10-30  Egeyar Bagcioglu <egeyar.bagcioglu@oracle.com>
> 
>     [AArch64] Use MOV (register) as an alias for ORR (shifted register)
>     iff shift == '00' && imm6 == '000000' && Rn == '11111'.
> 
>     gas/ChangeLog:
>         PR 23193
>         PR 19721
>         * testsuite/gas/aarch64/pr19721.s: Add new test cases.
>         * testsuite/gas/aarch64/pr19721.d: Correct existing test
>         cases and add new ones.
> 
>     opcodes/ChangeLog:
>         PR 23193
>         PR 19721
>         * aarch64-tbl.h: Use MOV (register) as an alias for ORR (shifted
>         register) iff shift == '00' && imm6 == '000000' && Rn == '11111'.
> 
> 
> Tested on aarch64-unknown-linux-gnu and showed no regressions.
> 
> Please take a look and apply if legitimate.
> 
> Regards,
> Egeyar
> 
> restrict-mov-alias-for-orr.patch
> 
> diff --git a/gas/testsuite/gas/aarch64/pr19721.d b/gas/testsuite/gas/aarch64/pr19721.d
> index a621ae5..785d2a2 100644
> --- a/gas/testsuite/gas/aarch64/pr19721.d
> +++ b/gas/testsuite/gas/aarch64/pr19721.d
> @@ -6,5 +6,8 @@ Disassembly of section \.text:
>  
>  0+000 <.*>:
>     0:	aa1103e7 	mov	x7, x17
> -   4:	aa1167e7 	mov	x7, x17, lsl #25
> -   8:	aa1167e7 	mov	x7, x17, lsl #25
> +   4:	aa1167e7 	orr	x7, xzr, x17, lsl #25
> +   8:	aa1167e7 	orr	x7, xzr, x17, lsl #25
> +   c:	aa4003e0 	orr	x0, xzr, x0, lsr #0
> +  10:	aa0007e0 	orr	x0, xzr, x0, lsl #1
> +  14:	aa0003d0 	orr	x16, x30, x0
> diff --git a/gas/testsuite/gas/aarch64/pr19721.s b/gas/testsuite/gas/aarch64/pr19721.s
> index cda068a..be2b508 100644
> --- a/gas/testsuite/gas/aarch64/pr19721.s
> +++ b/gas/testsuite/gas/aarch64/pr19721.s
> @@ -3,3 +3,6 @@
>  	mov	x7, x17
>  	mov	x7, x17, lsl 25
>  	orr	x7, xzr, x17, lsl 25
> +        orr     x0, xzr, x0, lsr #0	// shift == 01
> +        orr     x0, xzr, x0, lsl #1	// imm6 == 000001
> +        orr     x16, x30, x0		// Rn == 11110
> diff --git a/opcodes/aarch64-tbl.h b/opcodes/aarch64-tbl.h
> index b73007d..df56048 100644
> --- a/opcodes/aarch64-tbl.h
> +++ b/opcodes/aarch64-tbl.h
> @@ -3319,7 +3319,7 @@ struct aarch64_opcode aarch64_opcode_table[] =
>    CORE_INSN ("and", 0xa000000, 0x7f200000, log_shift, 0, OP3 (Rd, Rn, Rm_SFT), QL_I3SAMER, F_SF),
>    CORE_INSN ("bic", 0xa200000, 0x7f200000, log_shift, 0, OP3 (Rd, Rn, Rm_SFT), QL_I3SAMER, F_SF),
>    CORE_INSN ("orr", 0x2a000000, 0x7f200000, log_shift, 0, OP3 (Rd, Rn, Rm_SFT), QL_I3SAMER, F_HAS_ALIAS | F_SF),
> -  CORE_INSN ("mov", 0x2a0003e0, 0x7f2003e0, log_shift, 0, OP2 (Rd, Rm_SFT), QL_I2SAMER, F_ALIAS | F_SF),
> +  CORE_INSN ("mov", 0x2a0003e0, 0x7fe0ffe0, log_shift, 0, OP2 (Rd, Rm_SFT), QL_I2SAMER, F_ALIAS | F_SF),
>    CORE_INSN ("uxtw", 0x2a0003e0, 0x7f2003e0, log_shift, OP_UXTW, OP2 (Rd, Rm), QL_I2SAMEW, F_ALIAS | F_PSEUDO),
>    CORE_INSN ("orn", 0x2a200000, 0x7f200000, log_shift, 0, OP3 (Rd, Rn, Rm_SFT), QL_I3SAMER, F_HAS_ALIAS | F_SF),
>    CORE_INSN ("mvn", 0x2a2003e0, 0x7f2003e0, log_shift, 0, OP2 (Rd, Rm_SFT), QL_I2SAMER, F_ALIAS | F_SF),
>