Re: [PATCH v2] target/i386: Clear OF, SF, and AF for fcomi/fucomi

On 8/6/26 23:28, Simon Scherer wrote:
> helper_fcomi_ST0_FT0() and helper_fucomi_ST0_FT0() only cleared
> CC_Z, CC_P, and CC_C before merging in the comparison result,
> leaving CC_O, CC_S, and CC_A untouched from whatever they were
> set to beforehand.
> 
> The Intel SDM documents FCOMI/FCOMIP/FUCOMI/FUCOMIP as setting OF,
> SF, and AF to 0 unconditionally. The AMD manual doesn't mention them
> at all. However, testing on multiple real Intel and AMD systems confirms
> all three are unconditionally cleared regardless of the comparison
> result or their prior value.
> 
> Since fcomi_ccval[] only ever contains CC_C, CC_Z, 0, or CC_Z|CC_P|CC_C,
> and CC_O|CC_S|CC_Z|CC_A|CC_P|CC_C already covers every flag bit, CC_SRC
> can be assigned from fcomi_ccval[ret + 1] directly instead of ORing it
> into a masked cpu_cc_compute_all() result.
> 
> Resolves:https://gitlab.com/qemu-project/qemu/-/work_items/4133
> Signed-off-by: Simon Scherer<[email protected]>
> ---
> v2: Simplify per Richard Henderson's review: CC_O|CC_S|CC_A|CC_Z|CC_P|CC_C already covers
>      every flag, so drop the now-pointless cpu_cc_compute_all() call and assign
>      CC_SRC from fcomi_ccval[] directly.
> 
>   target/i386/tcg/fpu_helper.c | 10 ++++------
>   1 file changed, 4 insertions(+), 6 deletions(-)

Reviewed-by: Richard Henderson <[email protected]>

r~