http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54939
Bug #: 54939
Summary: Very poor vectorization of loops with complex
arithmetic
Classification: Unclassified
Product: gcc
Version: 4.8.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: ysrum...@gmail.com
Analyzing some performance anomaly for spec2000 I found out that 168.wupwise
with vectorization is slower than without it on x86. The main problem is that
gcc does not recognize some special idioms of complex addition and
multiplication in process of loop vectorization. For example, for a simple
zaxpy loop icc genearates 1.6X faster code than gcc. Here is assembly for zaxpy
loop produced by icc:
..B1.4: # Preds ..B1.2 ..B1.4
movups (%rsi,%rdx), %xmm2 #7.28
movups 16(%rsi,%rdx), %xmm5 #7.28
movups (%rsi,%rcx), %xmm4 #7.17
movups 16(%rsi,%rcx), %xmm7 #7.17
movddup (%rsi,%rdx), %xmm3 #7.27
incq %r8 #6.10
movddup 16(%rsi,%rdx), %xmm6 #7.27
unpckhpd %xmm2, %xmm2 #7.27
unpckhpd %xmm5, %xmm5 #7.27
mulpd %xmm1, %xmm3 #7.27
mulpd %xmm0, %xmm2 #7.27
mulpd %xmm1, %xmm6 #7.27
mulpd %xmm0, %xmm5 #7.27
addsubpd %xmm2, %xmm3 #7.27
addsubpd %xmm5, %xmm6 #7.27
addpd %xmm3, %xmm4 #7.9
addpd %xmm6, %xmm7 #7.9
movups %xmm4, (%rsi,%rcx) #7.9
movups %xmm7, 16(%rsi,%rcx) #7.9
addq $32, %rsi #6.10
cmpq %rdi, %r8 #6.10
jb ..B1.4 # Prob 64% #6.10
( I got it with -xSSE4.2 -O3 options). Gor gcc compiler the following options
were used: -m64 -mfpmath=sse -march=corei7 -O3 -ffast-math.
