Create a separate variable for compiler flags that enable
specific instruction set extensions, so that they can be used with
cc.compiles/cc.links.

Note that -mfpmath=sse is a code generation option but it does not
enable new instructions, therefore I did not make it part of
qemu_isa_flags.

Suggested-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
Cc: qemu-stable@nongnu.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 meson.build | 24 +++++++++++++++---------
 1 file changed, 15 insertions(+), 9 deletions(-)

diff --git a/meson.build b/meson.build
index 76335bb2a51..bbb0f6d9bcf 100644
--- a/meson.build
+++ b/meson.build
@@ -335,6 +335,10 @@ elif host_os == 'windows'
   endif
 endif
 
+# Choose instruction set (currently x86-only)
+
+qemu_isa_flags = []
+
 # __sync_fetch_and_and requires at least -march=i486. Many toolchains
 # use i686 as default anyway, but for those that don't, an explicit
 # specification is necessary
@@ -351,7 +355,7 @@ if host_arch == 'i386' and not cc.links('''
     sfaa(&val);
     return val;
   }''')
-  qemu_common_flags = ['-march=i486'] + qemu_common_flags
+  qemu_isa_flags = ['-march=i486']
 endif
 
 # Pick x86-64 baseline version
@@ -367,29 +371,31 @@ if host_arch in ['i386', 'x86_64']
     else
       # present on basically all processors but technically not part of
       # x86-64-v1, so only include -mneeded for x86-64 version 2 and above
-      qemu_common_flags = ['-mcx16'] + qemu_common_flags
+      qemu_isa_flags = ['-mcx16'] + qemu_isa_flags
     endif
   endif
   if get_option('x86_version') >= '2'
-    qemu_common_flags = ['-mpopcnt'] + qemu_common_flags
-    qemu_common_flags = cc.get_supported_arguments('-mneeded') + qemu_common_flags
+    qemu_isa_flags = ['-mpopcnt'] + qemu_isa_flags
+    qemu_isa_flags = cc.get_supported_arguments('-mneeded') + qemu_isa_flags
   endif
   if get_option('x86_version') >= '3'
-    qemu_common_flags = ['-mmovbe', '-mabm', '-mbmi', '-mbmi2', '-mfma', '-mf16c'] + qemu_common_flags
+    qemu_isa_flags = ['-mmovbe', '-mabm', '-mbmi', '-mbmi2', '-mfma', '-mf16c'] + qemu_isa_flags
   endif
 
   # add required vector instruction set (each level implies those below)
   if get_option('x86_version') == '1'
-    qemu_common_flags = ['-msse2'] + qemu_common_flags
+    qemu_isa_flags = ['-msse2'] + qemu_isa_flags
   elif get_option('x86_version') == '2'
-    qemu_common_flags = ['-msse4.2'] + qemu_common_flags
+    qemu_isa_flags = ['-msse4.2'] + qemu_isa_flags
   elif get_option('x86_version') == '3'
-    qemu_common_flags = ['-mavx2'] + qemu_common_flags
+    qemu_isa_flags = ['-mavx2'] + qemu_isa_flags
   elif get_option('x86_version') == '4'
-    qemu_common_flags = ['-mavx512f', '-mavx512bw', '-mavx512cd', '-mavx512dq', '-mavx512vl'] + qemu_common_flags
+    qemu_isa_flags = ['-mavx512f', '-mavx512bw', '-mavx512cd', '-mavx512dq', '-mavx512vl'] + qemu_isa_flags
   endif
 endif
 
+qemu_common_flags = qemu_isa_flags + qemu_common_flags
+
 if get_option('prefer_static')
   qemu_ldflags += get_option('b_pie') ? '-static-pie' : '-static'
 endif
-- 
2.46.1

On 10/7/24 01:43, Paolo Bonzini wrote:
> Create a separate variable for compiler flags that enable
> specific instruction set extensions, so that they can be used with
> cc.compiles/cc.links.
> 
> Note that -mfpmath=sse is a code generation option but it does not
> enable new instructions, therefore I did not make it part of
> qemu_isa_flags.
> 
> Suggested-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
> Cc: qemu-stable@nongnu.org
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>   meson.build | 24 +++++++++++++++---------
>   1 file changed, 15 insertions(+), 9 deletions(-)
> 
> diff --git a/meson.build b/meson.build
> index 76335bb2a51..bbb0f6d9bcf 100644
> --- a/meson.build
> +++ b/meson.build
> @@ -335,6 +335,10 @@ elif host_os == 'windows'
>     endif
>   endif
>   
> +# Choose instruction set (currently x86-only)
> +
> +qemu_isa_flags = []
> +
>   # __sync_fetch_and_and requires at least -march=i486. Many toolchains
>   # use i686 as default anyway, but for those that don't, an explicit
>   # specification is necessary
> @@ -351,7 +355,7 @@ if host_arch == 'i386' and not cc.links('''
>       sfaa(&val);
>       return val;
>     }''')
> -  qemu_common_flags = ['-march=i486'] + qemu_common_flags
> +  qemu_isa_flags = ['-march=i486']

Use += ?

> -      qemu_common_flags = ['-mcx16'] + qemu_common_flags
> +      qemu_isa_flags = ['-mcx16'] + qemu_isa_flags

Likewise, why verbosely prepend, rather than append with += ?
The same for all others, including

> +qemu_common_flags = qemu_isa_flags + qemu_common_flags


r~

07.10.2024 17:46, Richard Henderson пишет:
> On 10/7/24 01:43, Paolo Bonzini wrote:
>> Create a separate variable for compiler flags that enable
>> specific instruction set extensions, so that they can be used with
>> cc.compiles/cc.links.
>>
>> Note that -mfpmath=sse is a code generation option but it does not
>> enable new instructions, therefore I did not make it part of
>> qemu_isa_flags.
>>
>> Suggested-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
>> Cc: qemu-stable@nongnu.org
>> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
>> ---
>>   meson.build | 24 +++++++++++++++---------
>>   1 file changed, 15 insertions(+), 9 deletions(-)
>>
>> diff --git a/meson.build b/meson.build
>> index 76335bb2a51..bbb0f6d9bcf 100644
>> --- a/meson.build
>> +++ b/meson.build
>> @@ -335,6 +335,10 @@ elif host_os == 'windows'
>>     endif
>>   endif
>> +# Choose instruction set (currently x86-only)
>> +
>> +qemu_isa_flags = []
>> +
>>   # __sync_fetch_and_and requires at least -march=i486. Many toolchains
>>   # use i686 as default anyway, but for those that don't, an explicit
>>   # specification is necessary
>> @@ -351,7 +355,7 @@ if host_arch == 'i386' and not cc.links('''
>>       sfaa(&val);
>>       return val;
>>     }''')
>> -  qemu_common_flags = ['-march=i486'] + qemu_common_flags
>> +  qemu_isa_flags = ['-march=i486']
> 
> Use += ?

Yes, it is better to use += here - when reviewing the patch this is
obvious qemu_isa_flags is empty at this point, but it wont be as
obvious in the actual code when initial assignment is quite far away
from this prepending.


>> -      qemu_common_flags = ['-mcx16'] + qemu_common_flags
>> +      qemu_isa_flags = ['-mcx16'] + qemu_isa_flags
> 
> Likewise, why verbosely prepend, rather than append with += ?
> The same for all others, including
> 
>> +qemu_common_flags = qemu_isa_flags + qemu_common_flags

I'd keep prepending here (but not in qemu_isa_flags above) because this
way it is possible to override some flags by the user.

/mjt

On Mon, Oct 7, 2024 at 4:46 PM Richard Henderson
<richard.henderson@linaro.org> wrote:
> > -  qemu_common_flags = ['-march=i486'] + qemu_common_flags
> > +  qemu_isa_flags = ['-march=i486']
>
> Use += ?

Here the qemu_isa_flags are known to be empty.

> > -      qemu_common_flags = ['-mcx16'] + qemu_common_flags
> > +      qemu_isa_flags = ['-mcx16'] + qemu_isa_flags
>
> Likewise, why verbosely prepend, rather than append with += ?
> The same for all others, including
>
> > +qemu_common_flags = qemu_isa_flags + qemu_common_flags

The prepending behavior came from CPU_CFLAGS originally being before
all other compiler flags.

I just didn't want to change behavior here (especially since this
patch was already about subtle changes in behavior). But you're right
that at least within qemu_isa_flags the order should not matter.

Paolo

On 10/7/24 07:48, Paolo Bonzini wrote:
> On Mon, Oct 7, 2024 at 4:46 PM Richard Henderson
> <richard.henderson@linaro.org> wrote:
>>> -  qemu_common_flags = ['-march=i486'] + qemu_common_flags
>>> +  qemu_isa_flags = ['-march=i486']
>>
>> Use += ?
> 
> Here the qemu_isa_flags are known to be empty.

... until we add something else beforehand and fail to update.
Surely it's easier to assume that it's not empty.

> I just didn't want to change behavior here (especially since this
> patch was already about subtle changes in behavior). But you're right
> that at least within qemu_isa_flags the order should not matter.

Fair enough.


r~