[PATCH v2] aarch64: simplify RCPC3 unpredictable logic
Andrew Carlotti
andrew.carlotti@arm.com
Thu Mar 13 18:11:20 GMT 2025
On Fri, Mar 07, 2025 at 10:07:31AM +0100, Jan Beulich wrote:
> The original observation was that STILP is warned about when everything
> is fine. Documentation, not just for STILP, says explicitly that
> behavior is identical to respective pre-existing insns (for STILP in
> particular that's STP). With that it's unclear why distinct logic was
> added: Other code can be re-used, simply distinguishing by the number of
> operands. This was diagnostics also end up more consistent.
>
> Along with adding some STILP uses to the (positive) testcase, also add a
> pair of STLR to similarly demonstrate that the register overlap goes
> without warning when there's no write-back.
> ---
> See https://sourceware.org/pipermail/binutils/2024-August/136404.html.
>
> Note also how "load pair transfer" was quite odd in the diagnostic for
> STILP being a store, not a load.
> ---
> v2: Testcase adjustments as per review feedback.
Looks good to me now, though I can't approve it.
>
> --- a/gas/config/tc-aarch64.c
> +++ b/gas/config/tc-aarch64.c
> @@ -8465,6 +8465,7 @@ warn_unpredictable_ldst (aarch64_instruc
> case ldst_imm10:
> case ldst_unscaled:
> case ldst_unpriv:
> + ldst_single:
> /* Loading/storing the base register is unpredictable if writeback. */
> if ((aarch64_get_operand_class (opnds[0].type)
> == AARCH64_OPND_CLASS_INT_REG)
> @@ -8477,43 +8478,9 @@ warn_unpredictable_ldst (aarch64_instruc
> break;
>
> case rcpc3:
> - {
> - const int nb_operands = aarch64_num_of_operands (opcode);
> - if (aarch64_get_operand_class (opnds[0].type)
> - == AARCH64_OPND_CLASS_INT_REG)
> - {
> - /* Load Pair transfer with register overlap. */
> - if (nb_operands == 3 && opnds[0].reg.regno == opnds[1].reg.regno)
> - { // ldiapp, stilp
> - as_warn (_("unpredictable load pair transfer with register "
> - "overlap -- `%s'"),
> - str);
> - }
> - /* Loading/storing the base register is unpredictable if writeback. */
> - else if ((nb_operands == 2
> - && opnds[0].reg.regno == opnds[1].addr.base_regno
> - && opnds[1].addr.base_regno != REG_SP
> - && opnds[1].addr.writeback)
> - || (nb_operands == 3
> - && (opnds[0].reg.regno == opnds[2].addr.base_regno
> - || opnds[1].reg.regno == opnds[2].addr.base_regno)
> - && opnds[2].addr.base_regno != REG_SP
> - && opnds[2].addr.writeback))
> - {
> - if (strcmp (opcode->name, "ldapr") == 0
> - || strcmp (opcode->name, "ldiapp") == 0)
> - as_warn (
> - _("unpredictable transfer with writeback (load) -- `%s'"),
> - str);
> - else // stlr, stilp
> - as_warn (
> - _("unpredictable transfer with writeback (store) -- `%s'"),
> - str);
> - }
> - }
> - }
> - break;
> -
> + if (aarch64_num_of_operands (opcode) == 2)
> + goto ldst_single;
> + /* Fall through. */
> case ldstpair_off:
> case ldstnapair_offs:
> case ldstpair_indexed:
> --- a/gas/testsuite/gas/aarch64/rcpc3.d
> +++ b/gas/testsuite/gas/aarch64/rcpc3.d
> @@ -28,8 +28,10 @@ Disassembly of section \.text:
> [^:]+: 99010860 stilp w0, w1, \[x3, #-8\]!
> [^:]+: d9011820 stilp x0, x1, \[x1\]
> [^:]+: d9011800 stilp x0, x1, \[x0\]
> +[^:]+: d9001800 stilp x0, x0, \[x0\]
> [^:]+: 99011820 stilp w0, w1, \[x1\]
> [^:]+: 99011800 stilp w0, w1, \[x0\]
> +[^:]+: 99001800 stilp w0, w0, \[x0\]
> [^:]+: b8bfc020 ldapr w0, \[x1\]
> [^:]+: b8bfc020 ldapr w0, \[x1\]
> [^:]+: f8bfc020 ldapr x0, \[x1\]
> @@ -44,8 +46,10 @@ Disassembly of section \.text:
> [^:]+: d9c00be0 ldapr x0, \[sp\], #8
> [^:]+: 889ffc20 stlr w0, \[x1\]
> [^:]+: 889ffc20 stlr w0, \[x1\]
> +[^:]+: 889ffc00 stlr w0, \[x0\]
> [^:]+: c89ffc20 stlr x0, \[x1\]
> [^:]+: c89ffc20 stlr x0, \[x1\]
> +[^:]+: c89ffc00 stlr x0, \[x0\]
> [^:]+: 99800841 stlr w1, \[x2, #-4\]!
> [^:]+: d9800841 stlr x1, \[x2, #-8\]!
> [^:]+: d980081e stlr x30, \[x0, #-8\]!
> --- a/gas/testsuite/gas/aarch64/rcpc3.s
> +++ b/gas/testsuite/gas/aarch64/rcpc3.s
> @@ -29,8 +29,10 @@
> // for store is fine.
> stilp x0, x1, [x1]
> stilp x0, x1, [x0]
> + stilp x0, x0, [x0]
> stilp w0, w1, [x1]
> stilp w0, w1, [x0]
> + stilp w0, w0, [x0]
>
> ldapr w0, [x1]
> ldapr w0, [x1, #0]
> @@ -47,8 +49,10 @@
>
> stlr w0, [x1]
> stlr w0, [x1, #0]
> + stlr w0, [x0]
> stlr x0, [x1]
> stlr x0, [x1, #0]
> + stlr x0, [x0]
> stlr w1, [x2, #-4]!
> stlr x1, [x2, #-8]!
> stlr x30, [x0, #-8]!
> --- a/gas/testsuite/gas/aarch64/rcpc3-fail.l
> +++ b/gas/testsuite/gas/aarch64/rcpc3-fail.l
> @@ -51,27 +51,23 @@
> .*: Error: invalid increment amount at operand 2 -- `stlr x0,\[x1,#-4\]!'
> .*: Error: invalid increment amount at operand 2 -- `stlr w0,\[x1,#4\]!'
> .*: Error: invalid increment amount at operand 2 -- `stlr x0,\[x1,#8\]!'
> -.*: Warning: unpredictable load pair transfer with register overlap -- `ldiapp w0,w0,\[x1\]'
> -.*: Warning: unpredictable load pair transfer with register overlap -- `ldiapp x0,x0,\[x1\]'
> -.*: Warning: unpredictable load pair transfer with register overlap -- `ldiapp w0,w0,\[x1\],#8'
> -.*: Warning: unpredictable load pair transfer with register overlap -- `ldiapp x0,x0,\[x1\],#16'
> -.*: Warning: unpredictable load pair transfer with register overlap -- `stilp w0,w0,\[x1\]'
> -.*: Warning: unpredictable load pair transfer with register overlap -- `stilp x0,x0,\[x1\]'
> -.*: Warning: unpredictable load pair transfer with register overlap -- `stilp w0,w0,\[x1,#-8\]!'
> -.*: Warning: unpredictable load pair transfer with register overlap -- `stilp x0,x0,\[x1,#-16\]!'
> -.*: Warning: unpredictable transfer with writeback \(load\) -- `ldiapp x0,x1,\[x0\],#16'
> -.*: Warning: unpredictable transfer with writeback \(load\) -- `ldiapp x0,x1,\[x1\],#16'
> -.*: Warning: unpredictable transfer with writeback \(load\) -- `ldiapp w0,w1,\[x0\],#8'
> -.*: Warning: unpredictable transfer with writeback \(load\) -- `ldiapp w0,w1,\[x1\],#8'
> -.*: Warning: unpredictable transfer with writeback \(load\) -- `ldapr x0,\[x0\],#8'
> -.*: Warning: unpredictable transfer with writeback \(load\) -- `ldapr w0,\[x0\],#4'
> -.*: Warning: unpredictable transfer with writeback \(load\) -- `ldapr x1,\[x1\],#8'
> -.*: Warning: unpredictable transfer with writeback \(load\) -- `ldapr x30,\[x30\],#8'
> -.*: Warning: unpredictable transfer with writeback \(store\) -- `stilp x0,x1,\[x1,#-16\]!'
> -.*: Warning: unpredictable transfer with writeback \(store\) -- `stilp w0,w1,\[x1,#-8\]!'
> -.*: Warning: unpredictable transfer with writeback \(store\) -- `stilp x0,x1,\[x0,#-16\]!'
> -.*: Warning: unpredictable transfer with writeback \(store\) -- `stilp w0,w1,\[x0,#-8\]!'
> -.*: Warning: unpredictable transfer with writeback \(store\) -- `stlr x0,\[x0,#-8\]!'
> -.*: Warning: unpredictable transfer with writeback \(store\) -- `stlr w0,\[x0,#-4\]!'
> -.*: Warning: unpredictable transfer with writeback \(store\) -- `stlr x1,\[x1,#-8\]!'
> -.*: Warning: unpredictable transfer with writeback \(store\) -- `stlr x30,\[x30,#-8\]!'
> \ No newline at end of file
> +.*: Warning: unpredictable load of register pair -- `ldiapp w0,w0,\[x1\]'
> +.*: Warning: unpredictable load of register pair -- `ldiapp x0,x0,\[x1\]'
> +.*: Warning: unpredictable load of register pair -- `ldiapp w0,w0,\[x1\],#8'
> +.*: Warning: unpredictable load of register pair -- `ldiapp x0,x0,\[x1\],#16'
> +.*: Warning: unpredictable transfer with writeback -- `ldiapp x0,x1,\[x0\],#16'
> +.*: Warning: unpredictable transfer with writeback -- `ldiapp x0,x1,\[x1\],#16'
> +.*: Warning: unpredictable transfer with writeback -- `ldiapp w0,w1,\[x0\],#8'
> +.*: Warning: unpredictable transfer with writeback -- `ldiapp w0,w1,\[x1\],#8'
> +.*: Warning: unpredictable transfer with writeback -- `ldapr x0,\[x0\],#8'
> +.*: Warning: unpredictable transfer with writeback -- `ldapr w0,\[x0\],#4'
> +.*: Warning: unpredictable transfer with writeback -- `ldapr x1,\[x1\],#8'
> +.*: Warning: unpredictable transfer with writeback -- `ldapr x30,\[x30\],#8'
> +.*: Warning: unpredictable transfer with writeback -- `stilp x0,x1,\[x1,#-16\]!'
> +.*: Warning: unpredictable transfer with writeback -- `stilp w0,w1,\[x1,#-8\]!'
> +.*: Warning: unpredictable transfer with writeback -- `stilp x0,x1,\[x0,#-16\]!'
> +.*: Warning: unpredictable transfer with writeback -- `stilp w0,w1,\[x0,#-8\]!'
> +.*: Warning: unpredictable transfer with writeback -- `stlr x0,\[x0,#-8\]!'
> +.*: Warning: unpredictable transfer with writeback -- `stlr w0,\[x0,#-4\]!'
> +.*: Warning: unpredictable transfer with writeback -- `stlr x1,\[x1,#-8\]!'
> +.*: Warning: unpredictable transfer with writeback -- `stlr x30,\[x30,#-8\]!'
> --- a/gas/testsuite/gas/aarch64/rcpc3-fail.s
> +++ b/gas/testsuite/gas/aarch64/rcpc3-fail.s
> @@ -81,11 +81,6 @@
> ldiapp w0, w0, [x1], #8
> ldiapp x0, x0, [x1], #16
>
> - stilp w0, w0, [x1]
> - stilp x0, x0, [x1]
> - stilp w0, w0, [x1, #-8]!
> - stilp x0, x0, [x1, #-16]!
> -
> /* Invalid write back overlap (load)*/
> ldiapp x0, x1, [x0], #16
> ldiapp x0, x1, [x1], #16
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