Re: [PATCH 1/2] scripts/coccinelle: Add cpu_env.cocci_template script

["Philippe Mathieu-Daudé" <philmd@linaro.org>]

On 26/1/24 12:24, Paolo Bonzini wrote:
> On Fri, Jan 26, 2024 at 11:38 AM Philippe Mathieu-Daudé
> <philmd@linaro.org> wrote:
>>
>> On 25/1/24 17:56, Philippe Mathieu-Daudé wrote:
>>> Add a Coccinelle script to convert the following slow path
>>> (due to the QOM cast macro):
>>>
>>>     &ARCH_CPU(..)->env
>>>
>>> to the following fast path:
>>>
>>>     cpu_env(..)
>>>
>>> Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
>>> ---
>>>    MAINTAINERS                               |  1 +
>>>    scripts/coccinelle/cpu_env.cocci_template | 60 +++++++++++++++++++++++
>>>    2 files changed, 61 insertions(+)
>>>    create mode 100644 scripts/coccinelle/cpu_env.cocci_template
>>
>>
>>> diff --git a/scripts/coccinelle/cpu_env.cocci_template b/scripts/coccinelle/cpu_env.cocci_template
>>> new file mode 100644
>>> index 0000000000..53aa3a1fea
>>> --- /dev/null
>>> +++ b/scripts/coccinelle/cpu_env.cocci_template
>>> @@ -0,0 +1,60 @@
>>> +/*
>>> +
>>> + Convert &ARCH_CPU(..)->env to use cpu_env(..).
>>> +
>>> + Rationale: ARCH_CPU() might be slow, being a QOM cast macro.
>>> +            cpu_env() is its fast equivalent.
>>> +
>>> + SPDX-License-Identifier: GPL-2.0-or-later
>>> + SPDX-FileCopyrightText: Linaro Ltd 2024
>>> + SPDX-FileContributor: Philippe Mathieu-Daudé
>>> +
>>> + Usage as of v8.2.0:
>>> +
>>> + $ for targetdir in target/*; do test -d $targetdir || continue; \
>>> +       export target=${targetdir:7}; \
>>> +       sed \
>>> +           -e "s/__CPUArchState__/$( \
>>> +               git grep -h --no-line-number '@env: #CPU.*State' \
>>> +                   target/$target/cpu.h \
>>> +               | sed -n -e 's/.*\(CPU.*State\).\?/\1/p')/g" \
>>> +           -e "s/__ARCHCPU__/$( \
>>> +               git grep -h --no-line-number OBJECT_DECLARE_CPU_TYPE.*CPU \
>>> +                   target/$target/cpu-qom.h \
>>> +               | sed -n -e 's/.*(\(.*\), .*, .*)/\1/p')/g" \
>>> +           -e "s/__ARCH_CPU__/$( \
>>> +               git grep -h --no-line-number OBJECT_DECLARE_CPU_TYPE.*CPU \
>>> +                   target/$target/cpu-qom.h \
>>> +               | sed -n -e 's/.*(.*, .*, \(.*\))/\1/p')/g" \
>>> +       < scripts/coccinelle/cpu_env.cocci_template \
>>> +       > $TMPDIR/cpu_env_$target.cocci; \
>>> +       for dir in hw target/$target; do \
>>> +           spatch --macro-file scripts/cocci-macro-file.h \
>>> +                  --sp-file $TMPDIR/cpu_env_$target.cocci \
>>> +                  --keep-comments \
>>> +                  --dir $dir \
>>> +                  --in-place; \
>>> +       done; \
>>> +   done
>>> +
>>> +*/
>>> +
>>> +@ CPUState_arg_used @
>>> +CPUState *cs;
>>> +identifier cpu;
>>> +identifier env;
>>> +@@
>>> +-   __ARCHCPU__ *cpu = __ARCH_CPU__(cs);
>>
>> Here we remove ARCH_CPU(), ...
>>
>>> +-   __CPUArchState__ *env = &cpu->env;
>>> ++   __CPUArchState__ *env = cpu_env(cs);
>>> +    ... when != cpu
>>> +
>>> +@ depends on never CPUState_arg_used @
>>> +identifier obj;
>>> +identifier cpu;
>>> +identifier env;
>>> +@@
>>> +-   __ARCHCPU__ *cpu = __ARCH_CPU__(obj);
>>> +-   __CPUArchState__ *env = &cpu->env;
>>> ++   __CPUArchState__ *env = cpu_env(CPU(obj));
>>
>> ... but here we just change it by a CPU() QOM call.
>> So this 2nd change is just style cleanup.
> 
> Can you also add a hunk that is
> 
> CPUState *cs;
> @@
> -  CPU(cs)
> + cs
> 
> to clean up on the second?  cpu_env(CPU(current_cpu)) is suboptimal
> and also a bit ugly.

These case should be cleaned because this is already a CPUState*:

+    CPUX86State *env = cpu_env(CPU(current_cpu));

+    CPUPPCState *env = cpu_env(CPU(first_cpu));

But these (instance_init and QOM visitors) can't, the argument
isn't a CPUState*:

  static void ev4_cpu_initfn(Object *obj)
  {
-    AlphaCPU *cpu = ALPHA_CPU(obj);
-    CPUAlphaState *env = &cpu->env;
+    CPUAlphaState *env = cpu_env(CPU(obj));

@@ -5186,8 +5179,7 @@ static char *x86_cpuid_get_vendor(Object *obj, 
Error **errp)
  static void x86_cpuid_set_vendor(Object *obj, const char *value,
                                   Error **errp)
  {
-    X86CPU *cpu = X86_CPU(obj);
-    CPUX86State *env = &cpu->env;
+    CPUX86State *env = cpu_env(CPU(obj));

That said, these visitors take a Object* param because they implement
the generic QOM visitor API, but we know the visitor are registered
on classes/objects implementing CPUState, so QOM cast macro is
redundant.