On 7/28/25 17:02, Kyrylo Tkachov wrote:
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>
>
> Hi Spencer,
>
>> On 28 Jul 2025, at 16:25, Spencer Abson <spencer.ab...@arm.com> wrote:
>>
>> Streaming-compatible functions can be compiled without SME enabled, but need
>> to use "SMSTART SM" and "SMSTOP SM" to temporarily switch into the streaming
>> mode of a callee. These switches are conditional on the current mode being
>> opposite to the target mode, so no SME instructions are executed if SME is
>> not
>> available.
>>
>> However, in GAS, "SMSTART SM" and "SMSTOP SM" always require +sme. A call
>> from a streaming-compatible function, compiled without SME enabled, to a non
>> -streaming function will be rejected as:
> I guess this is an argument for allowing SMTART/SMSTOP in gas unconditionally?
> Though it would need to be consistent with LLVM and we’d still need a
> workaround for older binutils, so okay...
>
>
>> Error: selected processor does not support `smstop sm'..
>>
>> To work around this, we make use of the .inst directive to insert the literal
>> encodings of "SMSTART SM" and "SMSTOP SM".
>>
>> gcc/ChangeLog:
>> PR target/121028
>> * config/aarch64/aarch64-sme.md (aarch64_smstart_sm): Use the .inst
>> directive if !TARGET_SME.
>> (aarch64_smstop_sm): Likewise.
>>
>> gcc/testsuite/ChangeLog:
>> PR target/121028
>> * gcc.target/aarch64/sme/call_sm_switch_1.c: Tell check-function
>> -bodies not to ignore .inst directives, and replace the test for
>> "smstart sm" with one for it's encoding.
>> * gcc.target/aarch64/sme/call_sm_switch_11.c: Likewise.
>> * gcc.target/aarch64/sme/pr121028.c: New test.
>> ---
>> gcc/config/aarch64/aarch64-sme.md | 12 ++++-
>> .../gcc.target/aarch64/sme/call_sm_switch_1.c | 4 +-
>> .../aarch64/sme/call_sm_switch_11.c | 5 +-
>> .../gcc.target/aarch64/sme/pr121028.c | 46 +++++++++++++++++++
>> 4 files changed, 61 insertions(+), 6 deletions(-)
>> create mode 100644 gcc/testsuite/gcc.target/aarch64/sme/pr121028.c
>>
>> diff --git a/gcc/config/aarch64/aarch64-sme.md
>> b/gcc/config/aarch64/aarch64-sme.md
>> index 6b3f4390943..5264bf75c0b 100644
>> --- a/gcc/config/aarch64/aarch64-sme.md
>> +++ b/gcc/config/aarch64/aarch64-sme.md
>> @@ -62,6 +62,10 @@
>> ;; (b) they are sometimes used conditionally, particularly in streaming-
>> ;; compatible code.
>> ;;
>> +;; To prevent the latter from upsetting the assembler, we emit the literal
>> +;; encodings of "SMSTART SM" and "SMSTOP SM" when compiling without
>> +;; TARGET_SME.
>> +;;
>> ;; =========================================================================
>>
>> ;; -------------------------------------------------------------------------
>> @@ -161,7 +165,9 @@
>> (clobber (reg:VNx16BI P14_REGNUM))
>> (clobber (reg:VNx16BI P15_REGNUM))]
>> ""
>> - "smstart\tsm"
>> + {
>> + return TARGET_SME ? "smstart\tsm" : ".inst 0xd503437f";
>> + }
> Usually when we emit such .inst directives we also emit the mnemonic as an
> assembly comment to aid human assembly debugging.
> Ok by me with these changes, but maybe Richard is best-placed to comment on
> the SME parts.
> Thanks,
> Kyrill
>
>
>> )
>>
>> ;; Turn off streaming mode. This clobbers all SVE state.
>> @@ -196,7 +202,9 @@
>> (clobber (reg:VNx16BI P14_REGNUM))
>> (clobber (reg:VNx16BI P15_REGNUM))]
>> ""
>> - "smstop\tsm"
>> + {
>> + return TARGET_SME ? "smstop\tsm" : ".inst 0xd503427f";
>> + }
>> )
>>
>> ;; -------------------------------------------------------------------------
>> diff --git a/gcc/testsuite/gcc.target/aarch64/sme/call_sm_switch_1.c
>> b/gcc/testsuite/gcc.target/aarch64/sme/call_sm_switch_1.c
>> index 98922aaeae0..7d514bd46c1 100644
>> --- a/gcc/testsuite/gcc.target/aarch64/sme/call_sm_switch_1.c
>> +++ b/gcc/testsuite/gcc.target/aarch64/sme/call_sm_switch_1.c
>> @@ -1,5 +1,5 @@
>> // { dg-options "-O -fomit-frame-pointer -fno-optimize-sibling-calls
>> -funwind-tables" }
>> -// { dg-final { check-function-bodies "**" "" } }
>> +// { dg-final { check-function-bodies "**" "" "" { target "*-*-*" }
>> {\t\.inst} } }
>>
>> void ns_callee ();
>> void s_callee () [[arm::streaming]];
>> @@ -218,7 +218,7 @@ sc_caller_x1 (int *ptr, int a)
>> [[arm::streaming_compatible]]
>> ** bl ns_callee_stack
>> ** ldr x16, \[x29, #?16\]
>> ** tbz x16, 0, .*
>> -** smstart sm
>> +** .inst 0xd503437f
>> ** ...
>> */
>> void
>> diff --git a/gcc/testsuite/gcc.target/aarch64/sme/call_sm_switch_11.c
>> b/gcc/testsuite/gcc.target/aarch64/sme/call_sm_switch_11.c
>> index ee6f98737d9..7f1eab716eb 100644
>> --- a/gcc/testsuite/gcc.target/aarch64/sme/call_sm_switch_11.c
>> +++ b/gcc/testsuite/gcc.target/aarch64/sme/call_sm_switch_11.c
>> @@ -1,5 +1,6 @@
>> // { dg-options "-O -fomit-frame-pointer -fno-optimize-sibling-calls
>> -funwind-tables -mtrack-speculation" }
>> -// { dg-final { check-function-bodies "**" "" } }
>> +// { dg-final { check-function-bodies "**" "" "" { target "*-*-*" }
>> {\t\.inst} } }
>> +
>>
>> void ns_callee ();
>> void s_callee () [[arm::streaming]];
>> @@ -196,7 +197,7 @@ sc_caller_x1 (int *ptr, int a)
>> [[arm::streaming_compatible]]
>> ** tst x16, #?1
>> ** beq [^\n]*
>> ** csel x15, x15, xzr, ne
>> -** smstart sm
>> +** .inst 0xd503437f
>> ** ...
>> */
>> void
>> diff --git a/gcc/testsuite/gcc.target/aarch64/sme/pr121028.c
>> b/gcc/testsuite/gcc.target/aarch64/sme/pr121028.c
>> new file mode 100644
>> index 00000000000..fa36d4ec170
>> --- /dev/null
>> +++ b/gcc/testsuite/gcc.target/aarch64/sme/pr121028.c
>> @@ -0,0 +1,46 @@
>> +// PR121028
>> +// { dg-do assemble { target aarch64_asm_sme_ok } }
>> +// { dg-options "-O --save-temps" }
>> +// { dg-final { check-function-bodies "**" "" "" { target "*-*-*" }
>> {\t\.inst} } }
>> +
>> +void ns_callee ();
>> +
>> +/*
>> +** sc_caller_sme:
>> +** ...
>> +** mrs x16, svcr
>> +** str x16, \[x29, #?16\]
>> +** ldr x16, \[x29, #?16\]
>> +** tbz x16, 0, .*
>> +** smstop sm
>> +** bl ns_callee
>> +** ldr x16, \[x29, #?16\]
>> +** tbz x16, 0, .*
>> +** smstart sm
>> +** ...
>> +*/
>> +void sc_caller_sme() __arm_streaming_compatible
>> +{
>> + ns_callee ();
>> +}
>> +
>> +#pragma GCC target "+nosme"
>> +
>> +/*
>> +** sc_caller_nosme:
>> +** ...
>> +** bl __arm_sme_state
>> +** str x0, \[x29, #?16\]
>> +** ldr x16, \[x29, #?16\]
>> +** tbz x16, 0, .*
>> +** .inst 0xd503427f
>> +** bl ns_callee
>> +** ldr x16, \[x29, #?16\]
>> +** tbz x16, 0, .*
>> +** .inst 0xd503437f
>> +** ...
>> +*/
>> +void sc_caller_nosme() __arm_streaming_compatible
>> +{
>> + ns_callee ();
>> +}
>> --
>> 2.34.1
>>
Hi Spencer,
I don't see a signed-off-by, did I miss it?
Remi
