[LLVMdev] Testing the new CFL alias analysis

Thu Sep 18 10:10:21 PDT 2014

For CPU2006 4-copy specint rate runs, we measured some small gains ( 2%, 3% and 6% respectively ) for bzip2, gcc and sjeng, and some small losses ( -3% and -3% resp.) for h264ref and astar. This is for x86 and did not use PGO, but used LTO and -m32 (along with the new CFL alias flags). Overall, there is about  a 0.5% gain in specint rate.

-Dibyendu Das
AMD Compiler Group

-----Original Message-----
From: llvmdev-bounces at cs.uiuc.edu [mailto:llvmdev-bounces at cs.uiuc.edu] On Behalf Of Hal Finkel
Sent: Tuesday, September 16, 2014 7:06 AM
To: Gerolf Hoflehner
Cc: George Burgess IV; LLVM Dev
Subject: Re: [LLVMdev] Testing the new CFL alias analysis

----- Original Message -----
> From: "Gerolf Hoflehner" <ghoflehner at apple.com>
> To: "Hal Finkel" <hfinkel at anl.gov>
> Cc: "LLVM Dev" <llvmdev at cs.uiuc.edu>, "Jiangning Liu" <liujiangning1 at gmail.com>, "George Burgess IV"
> <george.burgess.iv at gmail.com>
> Sent: Monday, September 15, 2014 7:58:59 PM
> Subject: Re: [LLVMdev] Testing the new CFL alias analysis
> 
> I filed bugzilla pr20954.

Thanks!

 -Hal

> 
> 
> -Gerolf
> 
> 
> 
> 
> 
> 
> On Sep 15, 2014, at 2:56 PM, Gerolf Hoflehner < ghoflehner at apple.com
> > wrote:
> 
> 
> 
> On CINT2006 ARM64/ref input/lto+pgo I practically measure no 
> performance difference for the 7 benchmarks that compile. This 
> includes bzip2 (although different source base than in CINT2000), mcf, 
> hmmer, sjeng, h364ref, astar, xalancbmk
> 
> 
> 
> On Sep 15, 2014, at 11:59 AM, Hal Finkel < hfinkel at anl.gov > wrote:
> 
> 
> 
> ----- Original Message -----
> 
> 
> From: "Gerolf Hoflehner" < ghoflehner at apple.com >
> To: "Jiangning Liu" < liujiangning1 at gmail.com >, "George Burgess IV"
> < george.burgess.iv at gmail.com >, "Hal Finkel"
> < hfinkel at anl.gov >
> Cc: "LLVM Dev" < llvmdev at cs.uiuc.edu >
> Sent: Sunday, September 14, 2014 12:15:02 AM
> Subject: Re: [LLVMdev] Testing the new CFL alias analysis
> 
> In lto+pgo some (5 out of 12 with usual suspect like perlbench and gcc 
> among them using -flto -Wl,-mllvm,-use-cfl-aa
> -Wl,-mllvm,-use-cfl-aa-in-codegen) the CINT2006 benchmarks don’t 
> compile.
> 
> On what platform? Could you bugpoint it and file a report?
> Ok, I’ll see that I can get a small test case.
> 
> 
> 
> 
> 
> 
> Has the implementation been tested with lto?
> 
> I've not.
> 
> 
> 
> If not, please
> stress the implementation more.
> Do we know reasons for gains? Where did you expect the biggest gains?
> 
> I don't want to make a global statement here. My expectation is that 
> we'll see wins from increasing register pressure ;) -- hoisting more 
> loads out of loops (there are certainly cases involving 
> multiple-levels of dereferencing and insert/extract instructions where 
> CFL can provide a NoAlias answer where BasicAA gives up).
> Obviously, we'll also have problems if we increase pressure too much.
> 
> Maybe. But I prefer the OoO HW to handle hoisting though. It is hard 
> to tune in the compiler.
> I’m also curious about the impact on loop transformations.
> 
> 
> 
> 
> 
> Some of the losses will likely boil down to increased register 
> pressure.
> 
> Agreed.
> 
> 
> 
> 
> 
> Looks like the current performance numbers pose a good challenge for 
> gaining new and refreshing insights into our heuristics (and for 
> smoothing out the implementation along the way).
> 
> It certainly seems that way.
> 
> Thanks again,
> Hal
> 
> 
> 
> 
> 
> Cheers
> Gerolf
> 
> 
> 
> 
> 
> 
> 
> 
> 
> On Sep 12, 2014, at 1:27 AM, Jiangning Liu < liujiangning1 at gmail.com
> 
> 
> wrote:
> 
> 
> 
> Hi Hal,
> 
> I run on SPEC2000 on cortex-a57(AArch64), and got the following 
> results,
> 
> (It is to measure run-time reduction, and negative is better
> performance)
> 
> spec.cpu2000.ref.183_equake 33.77%
> spec.cpu2000.ref.179_art 13.44%
> spec.cpu2000.ref.256_bzip2 7.80%
> spec.cpu2000.ref.186_crafty 3.69%
> spec.cpu2000.ref.175_vpr 2.96%
> spec.cpu2000.ref.176_gcc 1.77%
> spec.cpu2000.ref.252_eon 1.77%
> spec.cpu2000.ref.254_gap 1.19%
> spec.cpu2000.ref.197_parser 1.15%
> spec.cpu2000.ref.253_perlbmk 1.11%
> spec.cpu2000.ref.300_twolf -1.04%
> 
> So we can see almost all got worse performance.
> 
> The command line option I'm using is "-O3 -std=gnu89 -ffast-math 
> -fslp-vectorize -fvectorize -mcpu=cortex-a57 -mllvm -use-cfl-aa -mllvm 
> -use-cfl-aa-in-codegen"
> 
> I didn't try compile-time, and I think your test on POWER7 native 
> build should already meant something for other hosts. Also I don't 
> have a good benchmark suit for compile time testing. My past 
> experiences showed both llvm-test-suite (single/multiple) and spec 
> benchmark are not good benchmarks for compile time testing.
> 
> Thanks,
> -Jiangning
> 
> 
> 2014-09-04 1:11 GMT+08:00 Hal Finkel < hfinkel at anl.gov > :
> 
> 
> Hello everyone,
> 
> One of Google's summer interns, George Burgess IV, created an 
> implementation of the CFL pointer-aliasing analysis algorithm, and 
> this has now been added to LLVM trunk. Now we should determine whether 
> it is worthwhile adding this to the default optimization pipeline. For 
> ease of testing, I've added the command line option -use-cfl-aa which 
> will cause the CFL analysis to be added to the optimization pipeline. 
> This can be used with the opt program, and also via Clang by passing: 
> -mllvm -use-cfl-aa.
> 
> For the purpose of testing with those targets that make use of 
> aliasing analysis during code generation, there is also a 
> corresponding -use-cfl-aa-in-codegen option.
> 
> Running the test suite on one of our IBM POWER7 systems (comparing
> -O3 -mcpu=native to -O3 -mcpu=native -mllvm -use-cfl-aa -mllvm 
> -use-cfl-aa-in-codegen [testing without use in code generation were 
> essentially the same]), I see no significant compile-time changes, and 
> the following performance results:
> speedup:
> MultiSource/Benchmarks/mafft/pairlocalalign: -11.5862% +/- 5.9257%
> 
> slowdown:
> MultiSource/Benchmarks/FreeBench/neural/neural: 158.679% +/- 22.3212%
> MultiSource/Benchmarks/MiBench/consumer-typeset/consumer-typeset:
> 0.627176% +/- 0.290698%
> MultiSource/Benchmarks/Ptrdist/ks/ks: 57.5457% +/- 21.8869%
> 
> I ran the test suite 20 times in each configuration, using make -j48 
> each time, so I'll only pick up large changes. I've not yet 
> investigated the cause of the slowdowns (or the speedup), and I really 
> need people to try this on x86, ARM, etc. I appears, however, the 
> better aliasing analysis results might have some negative unintended 
> consequences, and we'll need to look at those closely.
> 
> Please let me know how this fares on your systems!
> 
> Thanks again,
> Hal
> 
> --
> Hal Finkel
> Assistant Computational Scientist
> Leadership Computing Facility
> Argonne National Laboratory
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> 
> 
> --
> Hal Finkel
> Assistant Computational Scientist
> Leadership Computing Facility
> Argonne National Laboratory
> 

--
Hal Finkel
Assistant Computational Scientist
Leadership Computing Facility
Argonne National Laboratory

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