[llvm-dev] AVX 512 Assembly Code Generation

[hameeza ahmed via llvm-dev]

Hello,

I am using llvm  on my core i7 laptop which has no avx support.

my goal is to generate avx512 code (loop vectorization) for  Knight
landing/skylake .



my .c code is;

int a[256], b[256], c[256];
foo () {
int i;
for (i=0; i<256; i++) {
a[i] = b[i] + c[i];
}
}

i first generated its .ll file via clang

clang -S  -emit-llvm test.c -o test.ll

then i optimized it;

opt -S -O3 test.ll -o test_o3.ll

then i used llc for code generation

llc -mcpu=skylake-avx512 -mattr=+avx512f test_o3.ll -o test_o3.s

llc -mcpu=knl -mattr=+avx512f test_o3.ll -o test_o3.s


here is my generated code;



.text
.file "filer_o3.ll"
.globl foo
.p2align 4, 0x90
.type foo, at function
foo:                                    # @foo
.cfi_startproc
# BB#0:                                 # %min.iters.checked
pushq %rbp
.Ltmp0:
.cfi_def_cfa_offset 16
.Ltmp1:
.cfi_offset %rbp, -16
movq %rsp, %rbp
.Ltmp2:
.cfi_def_cfa_register %rbp
movq $-1024, %rax            # imm = 0xFC00
.p2align 4, 0x90
.*LBB0_1:                                # %vector.body*
*                                        # =>This Inner Loop Header:
Depth=1*
* vmovdqa32 c+1024(%rax), %xmm0*
* vmovdqa32 c+1040(%rax), %xmm1*
* vpaddd b+1024(%rax), %xmm0, %xmm0*
* vpaddd b+1040(%rax), %xmm1, %xmm1*
* vmovdqa32 %xmm0, a+1024(%rax)*
* vmovdqa32 %xmm1, a+1040(%rax)*
* vmovdqa32 c+1056(%rax), %xmm0*
* vmovdqa32 c+1072(%rax), %xmm1*
* vpaddd b+1056(%rax), %xmm0, %xmm0*
* vpaddd b+1072(%rax), %xmm1, %xmm1*
* vmovdqa32 %xmm0, a+1056(%rax)*
* vmovdqa32 %xmm1, a+1072(%rax)*
* addq $64, %rax*
* jne .LBB0_1*
# BB#2:                                 # %middle.block
popq %rbp
retq
.Lfunc_end0:
.size foo, .Lfunc_end0-foo
.cfi_endproc

.type b, at object               # @b
.comm b,1024,16
.type c, at object               # @c
.comm c,1024,16
.type a, at object               # @a
.comm a,1024,16

.ident "clang version 3.9.0 (tags/RELEASE_390/final)"
.section ".note.GNU-stack","", at progbits

in the generated code although there is use of vmov... instructions but no
zmm register? only xmm registers.


Can you please specify where i am wrong. i have tried it several times by
different parameters but always get xmm registers.


Thank You
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