On 06/16/2010 05:11 PM, Pavel Pavlov wrote:
>> -----Original Message-----
>> On 06/16/2010 01:15 PM, Andrew Haley wrote:
>>> On 06/16/2010 11:23 AM, Pavel Pavlov wrote:
> ...
>> inline uint64_t smlalbb(uint64_t acc, unsigned int lo, unsigned int hi) {
>> union
>> {
>> uint64_t ll;
>> struct
>> {
>> unsigned int l;
>> unsigned int h;
>> } s;
>> } retval;
>>
>> retval.ll = acc;
>>
>> __asm__("smlalbb %0, %1, %2, %3"
>> : "+r"(retval.s.l), "+r"(retval.s.h)
>> : "r"(lo), "r"(hi));
>>
>> return retval.ll;
>> }
>>
>
> [Pavel Pavlov]
> Later on I found out that I had to use +r constraint, but then, when I use that function for example like that:
> int64_t rsmlalbb64(int64_t i, int x, int y)
> {
> return smlalbb64(i, x, y);
> }
>
> Gcc generates this asm:
> <rsmlalbb64>:
> push {r4, r5}
> mov r4, r0
> mov ip, r1
> smlalbb r4, ip, r2, r3
> mov r5, ip
> mov r0, r4
> mov r1, ip
> pop {r4, r5}
> bx lr
>
> It's bizarre what gcc is doing in that function, I understand if it
> can't optimize and correctly use r0 and r1 directly, but from that
> listing it looks as if gcc got drunk and decided to touch r5 for
> absolutely no reason!
>
> the expected out should have been like that:
> <rsmlalbb64>:
> smlalbb r0, r1, r2, r3
> bx lr
>
> I'm using cegcc 4.1.0 and I compile with
> arm-mingw32ce-g++ -O3 -mcpu=arm1136j-s -c ARM_TEST.cpp -o ARM_TEST_GCC.obj
>
> Is there a way to access individual parts of that 64-bit input
> integer or, is there a way to specify that two 32-bit integers
> should be treated as a Hi:Lo parts of 64 bit variable. It's commonly
> done with a temporary, but the result is that gcc generates to much
> junk.
Why don't you just use the function I sent above? It generates
smlalbb:
smlalbb r0, r1, r2, r3
mov pc, lr
smlalXX64:
smlalbb r0, r1, r2, r3
smlalbt r0, r1, r2, r3
smlaltb r0, r1, r2, r3
smlaltt r0, r1, r2, r3
mov pc, lr
Andrew.
