[Openmp-dev] Phoronix numbers for clang-omp compiler

Jack Howarth howarth.mailing.lists at gmail.com
Wed Jun 4 11:19:49 PDT 2014 

Andrey,
     FSF gcc is not exactly defaulting to -O2 but certainly is higher than
the default optimizations on clang….

% touch t.cc
% g++-fsf-4.9 -fverbose-asm t.cc -S
% more t.s
# GNU C++ (GCC) version 4.9.0 (x86_64-apple-darwin11.4.2)
#       compiled by GNU C version 4.9.0, GMP version 6.0.0, MPFR version
3.1.2, MPC version 1.0.2
# GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
# options passed:  -D__DYNAMIC__ t.cc -fPIC -mmacosx-version-min=10.7.4
# -mtune=core2 -fverbose-asm
# options enabled:  -Wnonportable-cfstrings -fPIC
# -faggressive-loop-optimizations -fasynchronous-unwind-tables
# -fauto-inc-dec -fcommon -fdelete-null-pointer-checks -fearly-inlining
# -feliminate-unused-debug-types -fexceptions -ffunction-cse -fgcse-lm
# -fgnu-unique -fident -finline-atomics -fira-hoist-pressure
# -fira-share-save-slots -fira-share-spill-slots -fivopts
# -fkeep-static-consts -fleading-underscore -fmath-errno
# -fmerge-debug-strings -fnext-runtime -fobjc-abi-version= -fpeephole
# -fprefetch-loop-arrays -freg-struct-return
# -fsched-critical-path-heuristic -fsched-dep-count-heuristic
# -fsched-group-heuristic -fsched-interblock -fsched-last-insn-heuristic
# -fsched-rank-heuristic -fsched-spec -fsched-spec-insn-heuristic
# -fsched-stalled-insns-dep -fshow-column -fsigned-zeros
# -fsplit-ivs-in-unroller -fstrict-volatile-bitfields -fsync-libcalls
# -ftrapping-math -ftree-coalesce-vars -ftree-cselim -ftree-forwprop
# -ftree-loop-if-convert -ftree-loop-im -ftree-loop-ivcanon
# -ftree-loop-optimize -ftree-parallelize-loops= -ftree-phiprop
# -ftree-reassoc -ftree-scev-cprop -funit-at-a-time -funwind-tables
# -fverbose-asm -fzero-initialized-in-bss -gstrict-dwarf
# -m128bit-long-double -m64 -m80387 -malign-stringops -matt-stubs
# -mconstant-cfstrings -mfancy-math-387 -mfp-ret-in-387 -mfxsr -mieee-fp
# -mlong-double-80 -mmmx -mno-sse4 -mpush-args -mred-zone -msse -msse2
# -msse3

        .constructor
        .destructor
        .align 1
        .subsections_via_symbols

% g++-fsf-4.9 -fverbose-asm -O2 t.cc -S
% more t.s
# GNU C++ (GCC) version 4.9.0 (x86_64-apple-darwin11.4.2)
#       compiled by GNU C version 4.9.0, GMP version 6.0.0, MPFR version
3.1.2, MPC version 1.0.2
# GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
# options passed:  -D__DYNAMIC__ t.cc -fPIC -mmacosx-version-min=10.7.4
# -mtune=core2 -O2 -fverbose-asm
# options enabled:  -Wnonportable-cfstrings -fPIC
# -faggressive-loop-optimizations -fasynchronous-unwind-tables
# -fauto-inc-dec -fbranch-count-reg -fcaller-saves
# -fcombine-stack-adjustments -fcommon -fcompare-elim -fcprop-registers
# -fcrossjumping -fcse-follow-jumps -fdefer-pop
# -fdelete-null-pointer-checks -fdevirtualize -fdevirtualize-speculatively
# -fearly-inlining -feliminate-unused-debug-types -fexceptions
# -fexpensive-optimizations -fforward-propagate -ffunction-cse -fgcse
# -fgcse-lm -fgnu-unique -fguess-branch-probability -fhoist-adjacent-loads
# -fident -fif-conversion -fif-conversion2 -findirect-inlining -finline
# -finline-atomics -finline-functions-called-once -finline-small-functions
# -fipa-cp -fipa-profile -fipa-pure-const -fipa-reference -fipa-sra
# -fira-hoist-pressure -fira-share-save-slots -fira-share-spill-slots
# -fisolate-erroneous-paths-dereference -fivopts -fkeep-static-consts
# -fleading-underscore -fmath-errno -fmerge-constants -fmerge-debug-strings
# -fmove-loop-invariants -fnext-runtime -fobjc-abi-version=
# -fomit-frame-pointer -foptimize-sibling-calls -foptimize-strlen
# -fpartial-inlining -fpeephole -fpeephole2 -fprefetch-loop-arrays -free
# -freg-struct-return -freorder-blocks -freorder-blocks-and-partition
# -freorder-functions -frerun-cse-after-loop
# -fsched-critical-path-heuristic -fsched-dep-count-heuristic
# -fsched-group-heuristic -fsched-interblock -fsched-last-insn-heuristic
# -fsched-rank-heuristic -fsched-spec -fsched-spec-insn-heuristic
# -fsched-stalled-insns-dep -fschedule-insns2 -fshow-column -fshrink-wrap
# -fsigned-zeros -fsplit-ivs-in-unroller -fsplit-wide-types
# -fstrict-aliasing -fstrict-overflow -fstrict-volatile-bitfields
# -fsync-libcalls -fthread-jumps -ftoplevel-reorder -ftrapping-math
# -ftree-bit-ccp -ftree-builtin-call-dce -ftree-ccp -ftree-ch
# -ftree-coalesce-vars -ftree-copy-prop -ftree-copyrename -ftree-cselim
# -ftree-dce -ftree-dominator-opts -ftree-dse -ftree-forwprop -ftree-fre
# -ftree-loop-if-convert -ftree-loop-im -ftree-loop-ivcanon
# -ftree-loop-optimize -ftree-parallelize-loops= -ftree-phiprop -ftree-pre
# -ftree-pta -ftree-reassoc -ftree-scev-cprop -ftree-sink -ftree-slsr
# -ftree-sra -ftree-switch-conversion -ftree-tail-merge -ftree-ter
# -ftree-vrp -funit-at-a-time -funwind-tables -fverbose-asm
# -fzero-initialized-in-bss -gstrict-dwarf -m128bit-long-double -m64
# -m80387 -malign-stringops -matt-stubs -mconstant-cfstrings
# -mfancy-math-387 -mfp-ret-in-387 -mfxsr -mieee-fp -mlong-double-80 -mmmx
# -mno-sse4 -mpush-args -mred-zone -msse -msse2 -msse3 -mvzeroupper

        .constructor
        .destructor
        .align 1
        .subsections_via_symbols

You might consider filing an enhancement request for clang 3.5 to have the
default behavior without optimization flags bumped up to -O1.
         Jack



On Wed, Jun 4, 2014 at 11:02 AM, Andrey Bokhanko <andreybokhanko at gmail.com>
wrote:

> Hi All,
>
> Some of you probably saw performance benchmarking of OpenMP-enabled clang
> compiler published on Phoronix web-site:
> http://www.phoronix.com/scan.php?page=article&item=llvm_clang_openmp&num=1
>
> As you can see, clang-omp is behind gcc in most of the benchmarks. The
> reason is quite simple: no -O options supplied to both compilers, so gcc
> assumed -O2 by default, while clang assumed -O0. No surprise gcc got ahead!
>
> We added -O2 to clang and re-measured, and results changed quite
> significantly. My Intel colleague, Alexey Bataev, informed Michael Larabel
> on this omission.
>
> Yours,
> Andrey
> =====
> Software Engineer
> Intel Compiler Team
> Intel
>
>
> _______________________________________________
> Openmp-dev mailing list
> Openmp-dev at dcs-maillist2.engr.illinois.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/openmp-dev
>
>
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