https://llvm.org/bugs/show_bug.cgi?id=28109
Bug ID: 28109
Summary: byte order in xmm clang assembly comments
Product: clang
Version: 3.8
Hardware: PC
OS: Linux
Status: NEW
Severity: normal
Priority: P
Component: -New Bugs
Assignee: unassignedclangbugs at nondot.org
Reporter: albertnetymk at gmail.com
CC: llvm-bugs at lists.llvm.org
Classification: Unclassified
```
#include "emmintrin.h"
int main(int argc, char *argv[])
{
volatile __m128i x = _mm_set_epi64x(1, 0);
return 0;
}
```
Give above program, I could get the assembly using `clang -O -S test.c`:
```
...
movl $1, %eax
movd %rax, %xmm0
pslldq $8, %xmm0 # xmm0 =
zero,zero,zero,zero,zero,zero,zero,zero,xmm0[0,1,2,3,4,5,6,7]
...
```
According to the manual of
[_mm_set_epi64x](https://software.intel.com/sites/landingpage/IntrinsicsGuide/#text=_mm_set_epi&expand=4562,4565,4567),
`%xmm0` should be `[0, 1, 0, 0]`, with each element being an integer (32 bits).
However, according to the comment, `%xmm0` holds `[0, 0, 0, 1]`. I don't think
endianness is relevant here, for I am only looking at a register.
I suspect that it's sth related to the notation used by clang assembly comment,
but I can't find any useful info on it on the internet.
Reprinted from
http://stackoverflow.com/questions/37773274/byte-order-in-xmm-clang-assembly-comments
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