Re: [Qemu-devel] [PATCH 05/10] qemu-tech: document lazy condition code evaluation in cpu.h

[Paolo Bonzini <pbonzini@redhat.com>]

On 06/10/2016 18:18, Emilio G. Cota wrote:
> On Thu, Oct 06, 2016 at 17:24:18 +0200, Paolo Bonzini wrote:
>> Unlike the other sections, they are pretty specific to a particular CPU.
>>
>> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
>> ---
>>  qemu-tech.texi     | 25 -------------------------
>>  target-cris/cpu.h  |  7 +++++++
>>  target-i386/cpu.h  |  7 +++++++
>>  target-m68k/cpu.h  |  8 ++++++++
>>  target-sparc/cpu.h |  5 +++++
>>  5 files changed, 27 insertions(+), 25 deletions(-)
> (snip)
>> diff --git a/target-cris/cpu.h b/target-cris/cpu.h
>> index 7d7fe6e..6d3de56 100644
>> --- a/target-cris/cpu.h
>> +++ b/target-cris/cpu.h
>> @@ -223,6 +223,13 @@ int cpu_cris_signal_handler(int host_signum, void *pinfo,
>>  void cris_initialize_tcg(void);
>>  void cris_initialize_crisv10_tcg(void);
>>  
>> +/* Instead of computing the condition codes after each x86 instruction,
>> + * QEMU just stores one operand (called CC_SRC), the result
>> + * (called CC_DST) and the type of operation (called CC_OP). When the
>> + * condition codes are needed, the condition codes can be calculated
>> + * using this information. Condition codes are not generated if they
>> + * are only needed for conditional branches.
>> + */
> 
> This text doesn't seem to be cris-specific, e.g.:
> - "each x86 instruction"
> - CC_SRC (git grep CC_SRC here doesn't return anything)
> - CC_DST (ditto)

Yeah, it's cc_src and cc_dest.  The uppercase is a relic of dyngen
(pre-TCG).  Same for m68k.

Paolo

> 
>>  enum {
>>      CC_OP_DYNAMIC, /* Use env->cc_op  */
>>      CC_OP_FLAGS,
>> diff --git a/target-i386/cpu.h b/target-i386/cpu.h
>> index 6d028aa..f606f15 100644
>> --- a/target-i386/cpu.h
>> +++ b/target-i386/cpu.h
>> @@ -698,6 +698,13 @@ typedef uint32_t FeatureWordArray[FEATURE_WORDS];
>>  /* Use a clearer name for this.  */
>>  #define CPU_INTERRUPT_INIT      CPU_INTERRUPT_RESET
>>  
>> +/* Instead of computing the condition codes after each x86 instruction,
>> + * QEMU just stores one operand (called CC_SRC), the result
>> + * (called CC_DST) and the type of operation (called CC_OP). When the
>> + * condition codes are needed, the condition codes can be calculated
>> + * using this information. Condition codes are not generated if they
>> + * are only needed for conditional branches.
>> + */
>>  typedef enum {
>>      CC_OP_DYNAMIC, /* must use dynamic code to get cc_op */
>>      CC_OP_EFLAGS,  /* all cc are explicitly computed, CC_SRC = flags */
>> diff --git a/target-m68k/cpu.h b/target-m68k/cpu.h
>> index c2d40cb..ccc7157 100644
>> --- a/target-m68k/cpu.h
>> +++ b/target-m68k/cpu.h
>> @@ -154,6 +154,14 @@ int cpu_m68k_signal_handler(int host_signum, void *pinfo,
>>                             void *puc);
>>  void cpu_m68k_flush_flags(CPUM68KState *, int);
>>  
>> +
>> +/* Instead of computing the condition codes after each x86 instruction,
>> + * QEMU just stores one operand (called CC_SRC), the result
>> + * (called CC_DST) and the type of operation (called CC_OP). When the
>> + * condition codes are needed, the condition codes can be calculated
>> + * using this information. Condition codes are not generated if they
>> + * are only needed for conditional branches.
>> + */
> 
> Same as above:
> - "each x86 instruction"
> - no CC_DST
> 
> 		Emilio
>