Re: [PATCH v2] sh4: mac.l: implement saturation arithmetic logic

[Richard Henderson <richard.henderson@linaro.org>]

On 4/4/24 06:26, Zack Buhman wrote:
> The saturation arithmetic logic in helper_macl is not correct.
> 
> I tested and verified this behavior on a SH7091, the general pattern
> is a code sequence such as:
> 
> 	sets
> 
> 	mov.l _mach,r2
> 	lds r2,mach
> 	mov.l _macl,r2
> 	lds r2,macl
> 
> 	mova _n,r0
> 	mov r0,r1
> 	mova _m,r0
> 	mac.l @r0+,@r1+
> 
>      _mach: .long 0x00007fff
>      _macl: .long 0x12345678
>      _m:    .long 0x7fffffff
>      _n:    .long 0x7fffffff
> 
> Test case 0: (no int64_t overflow)
>    given; prior to saturation mac.l:
>      mach = 0x00007fff macl = 0x12345678
>      @r0  = 0x7fffffff @r1  = 0x7fffffff
> 
>    expected saturation mac.l result:
>      mach = 0x00007fff macl = 0xffffffff
> 
>    qemu saturation mac.l result (prior to this commit):
>      mach = 0x00007ffe macl = 0x12345678
> 
> Test case 1: (no int64_t overflow)
>    given; prior to saturation mac.l:
>      mach = 0xffff8000 macl = 0x00000000
>      @r0  = 0xffffffff @r1  = 0x00000001
> 
>    expected saturation mac.l result:
>      mach = 0xffff8000 macl = 0x00000000
> 
>    qemu saturation mac.l result (prior to this commit):
>      mach = 0xffff7fff macl = 0xffffffff
> 
> Test case 2: (int64_t addition overflow)
>    given; prior to saturation mac.l:
>      mach = 0x80000000 macl = 0x00000000
>      @r0  = 0xffffffff @r1  = 0x00000001
> 
>    expected saturation mac.l result:
>      mach = 0xffff8000 macl = 0x00000000
> 
>    qemu saturation mac.l result (prior to this commit):
>      mach = 0xffff7fff macl = 0xffffffff
> 
> Test case 3: (int64_t addition overflow)
>    given; prior to saturation mac.l:
>      mach = 0x7fffffff macl = 0x00000000
>      @r0 = 0x7fffffff @r1 = 0x7fffffff
> 
>    expected saturation mac.l result:
>      mach = 0x00007fff macl = 0xffffffff
> 
>    qemu saturation mac.l result (prior to this commit):
>      mach = 0xfffffffe macl = 0x00000001
> 
> All of the above also matches the description of MAC.L as documented
> in cd00147165-sh-4-32-bit-cpu-core-architecture-stmicroelectronics.pdf
> ---
>   target/sh4/op_helper.c | 31 +++++++++++++++++++++----------
>   1 file changed, 21 insertions(+), 10 deletions(-)

Queued, thanks.


r~