Re: [Tinycc-devel] SSE calling convention bug

[Christian Jullien]

My remark is from principle that "a function should tell what it does and does 
what it tells"

-----Original Message-----
From: Tinycc-devel [mailto:tinycc-devel-bounces+eligis=address@hidden] On 
Behalf Of Herman ten Brugge via Tinycc-devel
Sent: Tuesday, October 29, 2019 10:37
To: address@hidden
Cc: Herman ten Brugge
Subject: Re: [Tinycc-devel] SSE calling convention bug

Do you mean that I should call the testcase '109_calling.c' and add a 
comment in this file that this is for x86_64 sse calling?

This is why I called the file '109_sse_calling.c'.

The file name indicates that this is only solving a bug for x86_64.

     Herman



On 2019-10-29 08:04, Christian Jullien wrote:
> Than you for your recent patch on mod.
>
> I just have a little remark about ' 109_sse_calling' file name.
> This new test is executed also on Windows and arm32/64 (which is fine). 
> However, those backend don't use sse.
> IMHO, this test should not have sse in its name but a comment could explain 
> that the test revealed a bug when see is used as with Linux.
>
> Another solution is to add this new test in 22_floating_point + comment about 
> sse
>
> -----Original Message-----
> From: Tinycc-devel [mailto:tinycc-devel-bounces+eligis=address@hidden] On 
> Behalf Of Michael Matz
> Sent: Monday, October 28, 2019 10:32
> To: Herman ten Brugge via Tinycc-devel
> Cc: Herman ten Brugge
> Subject: *** SPAM *** Re: [Tinycc-devel] SSE calling convention bug
>
> Hi,
>
> On Sun, 27 Oct 2019, Herman ten Brugge via Tinycc-devel wrote:
>
>> Look like the code in x86_64-gen.c is wrong. It should read:
>>
>>                  if (sse_reg) { /* avoid redundant movaps %xmm0, %xmm0
>> */
>>                      /* movaps %xmm1, %xmmN */
>>                      o(0x280f);
>>                      o(0xc1 + ((sse_reg+1) << 3));
>>                      /* movaps %xmm0, %xmmN */
>>                      o(0x280f);
>>                      o(0xc0 + (sse_reg << 3));
>>                  }
> Yes.
>
>
> Ciao,
> Michael.
>
>> The problem occurs when sse_reg == 1. Because then xmm1 is overwritten
>> before it is copied.
>>
>>      Herman
>>
>> On 2019-10-27 07:32, Christian Jullien wrote:
>>> Trying your sample with mod on Windows -m64/-m32 I get:
>>>
>>> c: >tcc -m32 foo.c && foo
>>> 5.000000
>>>
>>> c:>tcc -m64 foo.c && foo
>>> 5.000000
>>>
>>> It only return 3.0000 on Linux x64 (I've not tested your code on Linux x86).
>>>
>>> C.
>>>
>>>
>>> -----Original Message-----
>>> From: Tinycc-devel
>>> [mailto:tinycc-devel-bounces+eligis=address@hidden]
>>> On Behalf Of Shachaf Ben-Kiki
>>> Sent: Saturday, October 26, 2019 12:59
>>> To: address@hidden
>>> Subject: [Tinycc-devel] SSE calling convention bug
>>>
>>> Hello,
>>>
>>> I ran into a bug in the SSE function call code in x86_64-gen.c. It's
>>> in the following lines, in gfunc_call:
>>>
>>>                   if (sse_reg) { /* avoid redundant movaps %xmm0, %xmm0 */
>>>                       /* movaps %xmm0, %xmmN */
>>>                       o(0x280f);
>>>                       o(0xc0 + (sse_reg << 3));
>>>                       /* movaps %xmm1, %xmmN */
>>>                       o(0x280f);
>>>                       o(0xc1 + ((sse_reg+1) << 3));
>>>                   }
>>>
>>> When sse_reg is %xmm1, this generates
>>>
>>>       0f 28 c8                movaps %xmm0,%xmm1
>>>       0f 28 d1                movaps %xmm1,%xmm2
>>>
>>> Such that the first mov overwrites xmm1 before the second mov uses it.
>>> Since the registers are used in reverse order and only one or two at
>>> a time, I think swapping the order of the movs should be sufficient
>>> to fix it.
>>>
>>> Here's a test case:
>>>
>>> #include <stdio.h>
>>>
>>> struct Point {
>>>     float x;
>>>     float y;
>>> };
>>>
>>> struct Rect {
>>>     struct Point top_left;
>>>     struct Point size;
>>> };
>>>
>>> float foo(struct Point p, struct Rect r) {
>>>     return r.size.x;
>>> }
>>>
>>> int main(int argc, char **argv) {
>>>     struct Point p = {1, 2};
>>>     struct Rect r = {{3, 4}, {5, 6}};
>>>     printf("%f\n", foo(p, r));
>>>     return 0;
>>> }
>>>
>>> This program should print 5, but it prints 3 in tcc.
>>>
>>> Is this the right place to post this? I can post it elsewhere, or
>>> send a patch (it took a while to track this down but I think the fix
>>> should be easy).
>>>
>>> Thanks,
>>>       Shachaf
>>>
>>> _______________________________________________
>>> Tinycc-devel mailing list
>>> address@hidden
>>> https://lists.nongnu.org/mailman/listinfo/tinycc-devel
>>>
>>>
>>
>> _______________________________________________
>> Tinycc-devel mailing list
>> address@hidden
>> https://lists.nongnu.org/mailman/listinfo/tinycc-devel
>>
>>


_______________________________________________
Tinycc-devel mailing list
address@hidden
https://lists.nongnu.org/mailman/listinfo/tinycc-devel