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[Bug tree-optimization/31079] 20% difference between ifort/gfortran, missed vectorization
- From: "jv244 at cam dot ac dot uk" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: 19 Aug 2008 06:09:50 -0000
- Subject: [Bug tree-optimization/31079] 20% difference between ifort/gfortran, missed vectorization
- References: <bug-31079-6642@http.gcc.gnu.org/bugzilla/>
- Reply-to: gcc-bugzilla at gcc dot gnu dot org
------- Comment #11 from jv244 at cam dot ac dot uk 2008-08-19 06:09 -------
Created an attachment (id=16095)
--> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=16095&action=view)
new testcase
This (PR31079_11.f90) should be a replacement for comment #4, and illustrates
the vectorizer issue.
> gfortran -O3 -ftree-vectorize -ffast-math -march=native PR31079_11.f90
> ./a.out
4.0282512
> ifort -O3 -xT PR31079_11.f90
PR31079_11.f90(52): (col. 13) remark: LOOP WAS VECTORIZED.
PR31079_11.f90(52): (col. 13) remark: BLOCK WAS VECTORIZED.
PR31079_11.f90(52): (col. 13) remark: LOOP WAS VECTORIZED.
PR31079_11.f90(52): (col. 13) remark: LOOP WAS VECTORIZED.
PR31079_11.f90(17): (col. 8) remark: LOOP WAS VECTORIZED.
PR31079_11.f90(24): (col. 5) remark: BLOCK WAS VECTORIZED.
PR31079_11.f90(30): (col. 7) remark: LOOP WAS VECTORIZED.
PR31079_11.f90(31): (col. 7) remark: LOOP WAS VECTORIZED.
> ./a.out
2.640165
The inner loop looks like:
DO i=1,N
s(1:2)=s(1:2)+pxy(i)%a(:)*dpy(i)%a(1)
s(3:4)=s(3:4)+pxy(i)%a(:)*dpy(i)%a(2)
ENDDO
which ifort vectorizes (I will attach the full asm):
..B3.4: # Preds ..B3.4 ..B3.3
movddup collocate_core_2_2_0_0_$DPY.0.1(%rax), %xmm2 #30.33
movddup 8+collocate_core_2_2_0_0_$DPY.0.1(%rax), %xmm4 #31.33
movaps collocate_core_2_2_0_0_$PXY.0.1(%rax), %xmm3 #30.7
mulpd %xmm3, %xmm2 #30.32
incq %rdx #29.5
addq $16, %rax #29.5
addpd %xmm2, %xmm1 #30.7
cmpq $1000, %rdx #29.5
mulpd %xmm3, %xmm4 #31.32
addpd %xmm4, %xmm0 #31.7
jl ..B3.4 # Prob 99% #29.5
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31079