Hi,
First of all, does LLVM essentially fma or muladd expressions like `a1*x1
+ a2*x2 + a3*x3 + a4*x4`? Or is it required that one explicitly use
`muladd` and `fma` on these types of instructions (is there a macro for
making this easier)?
Secondly, I am wondering if my setup is no applying these operations
correctly. Here's my test code:
f(x) = 2.0x + 3.0
g(x) = muladd(x,2.0, 3.0)
h(x) = fma(x,2.0, 3.0)
@code_llvm f(4.0)
@code_llvm g(4.0)
@code_llvm h(4.0)
@code_native f(4.0)
@code_native g(4.0)
@code_native h(4.0)
*Computer 1*
Julia Version 0.5.0-rc4+0
Commit 9c76c3e* (2016-09-09 01:43 UTC)
Platform Info:
System: Linux (x86_64-redhat-linux)
CPU: Intel(R) Xeon(R) CPU E5-2667 v4 @ 3.20GHz
WORD_SIZE: 64
BLAS: libopenblas (DYNAMIC_ARCH NO_AFFINITY Haswell)
LAPACK: libopenblasp.so.0
LIBM: libopenlibm
LLVM: libLLVM-3.7.1 (ORCJIT, broadwell)
(the COPR nightly on CentOS7) with
[crackauc@crackauc2 ~]$ lscpu
Architecture: x86_64
CPU op-mode(s): 32-bit, 64-bit
Byte Order: Little Endian
CPU(s): 16
On-line CPU(s) list: 0-15
Thread(s) per core: 1
Core(s) per socket: 8
Socket(s): 2
NUMA node(s): 2
Vendor ID: GenuineIntel
CPU family: 6
Model: 79
Model name: Intel(R) Xeon(R) CPU E5-2667 v4 @ 3.20GHz
Stepping: 1
CPU MHz: 1200.000
BogoMIPS: 6392.58
Virtualization: VT-x
L1d cache: 32K
L1i cache: 32K
L2 cache: 256K
L3 cache: 25600K
NUMA node0 CPU(s): 0-7
NUMA node1 CPU(s): 8-15
I get the output
define double @julia_f_72025(double) #0 {
top:
%1 = fmul double %0, 2.000000e+00
%2 = fadd double %1, 3.000000e+00
ret double %2
}
define double @julia_g_72027(double) #0 {
top:
%1 = call double @llvm.fmuladd.f64(double %0, double 2.000000e+00, double
3.000000e+00)
ret double %1
}
define double @julia_h_72029(double) #0 {
top:
%1 = call double @llvm.fma.f64(double %0, double 2.000000e+00, double
3.000000e+00)
ret double %1
}
.text
Filename: fmatest.jl
pushq %rbp
movq %rsp, %rbp
Source line: 1
addsd %xmm0, %xmm0
movabsq $139916162906520, %rax # imm = 0x7F40C5303998
addsd (%rax), %xmm0
popq %rbp
retq
nopl (%rax,%rax)
.text
Filename: fmatest.jl
pushq %rbp
movq %rsp, %rbp
Source line: 2
addsd %xmm0, %xmm0
movabsq $139916162906648, %rax # imm = 0x7F40C5303A18
addsd (%rax), %xmm0
popq %rbp
retq
nopl (%rax,%rax)
.text
Filename: fmatest.jl
pushq %rbp
movq %rsp, %rbp
movabsq $139916162906776, %rax # imm = 0x7F40C5303A98
Source line: 3
movsd (%rax), %xmm1 # xmm1 = mem[0],zero
movabsq $139916162906784, %rax # imm = 0x7F40C5303AA0
movsd (%rax), %xmm2 # xmm2 = mem[0],zero
movabsq $139925776008800, %rax # imm = 0x7F43022C8660
popq %rbp
jmpq *%rax
nopl (%rax)
It looks like explicit muladd or not ends up at the same native code, but
is that native code actually doing an fma? The fma native is different, but
from a discussion on the Gitter it seems that might be a software FMA? This
computer is setup with the BIOS setting as LAPACK optimized or something
like that, so is that messing with something?
*Computer 2*
Julia Version 0.6.0-dev.557
Commit c7a4897 (2016-09-08 17:50 UTC)
Platform Info:
System: NT (x86_64-w64-mingw32)
CPU: Intel(R) Core(TM) i7-4770K CPU @ 3.50GHz
WORD_SIZE: 64
BLAS: libopenblas (USE64BITINT DYNAMIC_ARCH NO_AFFINITY Haswell)
LAPACK: libopenblas64_
LIBM: libopenlibm
LLVM: libLLVM-3.7.1 (ORCJIT, haswell)
on a 4770k i7, Windows 10, I get the output
; Function Attrs: uwtable
define double @julia_f_66153(double) #0 {
top:
%1 = fmul double %0, 2.000000e+00
%2 = fadd double %1, 3.000000e+00
ret double %2
}
; Function Attrs: uwtable
define double @julia_g_66157(double) #0 {
top:
%1 = call double @llvm.fmuladd.f64(double %0, double 2.000000e+00, double
3.000000e+00)
ret double %1
}
; Function Attrs: uwtable
define double @julia_h_66158(double) #0 {
top:
%1 = call double @llvm.fma.f64(double %0, double 2.000000e+00, double
3.000000e+00)
ret double %1
}
.text
Filename: console
pushq %rbp
movq %rsp, %rbp
Source line: 1
addsd %xmm0, %xmm0
movabsq $534749456, %rax # imm = 0x1FDFA110
addsd (%rax), %xmm0
popq %rbp
retq
nopl (%rax,%rax)
.text
Filename: console
pushq %rbp
movq %rsp, %rbp
Source line: 2
addsd %xmm0, %xmm0
movabsq $534749584, %rax # imm = 0x1FDFA190
addsd (%rax), %xmm0
popq %rbp
retq
nopl (%rax,%rax)
.text
Filename: console
pushq %rbp
movq %rsp, %rbp
movabsq $534749712, %rax # imm = 0x1FDFA210
Source line: 3
movsd dcabs164_(%rax), %xmm1 # xmm1 = mem[0],zero
movabsq $534749720, %rax # imm = 0x1FDFA218
movsd (%rax), %xmm2 # xmm2 = mem[0],zero
movabsq $fma, %rax
popq %rbp
jmpq *%rax
nop
This seems to be similar to the first result.
