[LLVMdev] RFC: TileGX, a new backend for Tilera's many core processor

[Jiong Wang]

On 03/01/2013 02:57 PM, Hal Finkel wrote:
Hi Hal,

   thanks for feedback.
> Jiong, I am happy to see the Tile backend being offered for upstream inclusion. Among other things, in the long run, this may help inform and motivate many-core capabilities in LLVM.
>
> First, can you elaborate on the future maintenance and development plans for the target code? Do you plan to add SIMD support? Atomic memory operations?
       yes, currently we lack of old JIT support (I was thinking MCJIT 
will be the future, but from the mailinglist archive, it seems old JIT 
is still necessary), SIMD intrinsic support etc. all these will be 
supported next.

       As some of the llvm modules are in active development, for 
example MC Layer, we want to return code to community repository first, 
so that it will be easy to keep pace with llvm main tree.
>
> Will you be able to setup a buildbot on this architecture? If so, can it be connected to the public system?
       yes, I guess it's OK to setup a tilegx buildbot with connection 
to public system. I will confirm this with the company.
>
> On the patch itself:
>
>   1. There are still a few places where there is commented-out code or #if 0 blocks; these should be removed (or replaced with real comments as appropriate).
       thanks, I will fix these things.
>
>   2. There are no regression tests -- using the test-suite is obviously useful, but targeted regression tests are essential.
        yes, regression tests will be added later.
>
> You say that there are unexpected failures in the regression tests and in the test suite. Do you understand these?
        yes, I have done investigation on these failures.

        regression (44 failures)
        ===
          20: caused JITTests failures, we lack old jit support
          2:
             MCJIT/test-common-symbols-remote.ll
             MCJIT/test-fp-no-external-funcs-remote.ll

         the other 20 are mostly under Clang:: Tooling (these testcases 
seems to be added in this week) & some debuginfo testcases,  I will 
clean up them later.


        test-suite (17 failures)
        ======
            1 of them are compile stage failures
             ===
                   MultiSource/Benchmarks/tramp3d-v4/tramp3d-v4
                   the reason is tilegx do not support some c99 float 
rounding & exceptions
                   we lack the support of some flag like FE_DIVBYZERO 
etc, for fegetexceptflag.

            16 of them are runtime failures.
             ===
                   actually, I compare all these failures with our gcc 
output, it's the same.
                   nearly all of them are caused by float point 
precision issue, for example,

  MultiSource/Applications/sqlite3/

  ...
  6|496148.333333333
-6|496234.333333333  <=== expected output & x86_64 result
+6|496234.333333334  <=== tilegx gcc/llvm result
  8|496373.0
  8|496448.375
  1|496587.0
-6|496647.333333333
+6|496647.333333334
  ...

---
Regards,
Jiong

>
>   -Hal
>
>> TILE-Gx is a VLIW architecture with 64-bit registers, 64-bit address
>> space,
>> and 64-bit instructions. TILE-Gx has load-store architecture ISAs.
>>
>> More information on the architectures is available at
>> http://www.tilera.com/scm/docs/index.html.
>>
>> the attached patches contains the following main features for tilegx
>> backend:
>>
>> 1. general function.
>> 2. PIC/TLS/JumpTable.
>> 3. Instructoin Bundling for VLIW.
>> 4. Basic support for Asm Parser.
>> 5. MC Layer (aware of VLIW), MCJIT support.
>>
>> I've run the regression test and standalone test-suite natively on
>> TILE-Gx silicon. The
>> test results are:
>>
>> regression
>> ---
>> Expected Passes : 13218
>> Expected Failures : 78
>> Unsupported Tests : 68
>> Unexpected Failures: 44
>>
>> test-suite
>> ---
>> Expected Passes : 949
>> Unexpected Failures: 17
>>
>> the llvm patch is against:
>>
>> commit 5e812139690ce077d568ef6559992b2cf74eb536
>> Author: Evgeniy Stepanov <eugeni.stepanov at gmail.com>
>> Date: Thu Feb 28 11:25:14 2013 +0000
>>
>> [msan] Implement sanitize_memory attribute.
>>
>> the clang patch is against:
>>
>> commit a4d4621b206f941cc58d9d0bc7c67a8e705c9d49
>> Author: Daniel Jasper <djasper at google.com>
>> Date: Thu Feb 28 11:05:57 2013 +0000
>>
>> Improve formatting of #defines.
>>
>> the test-suite patch is against:
>>
>> commit 8c1ab3b660e67b74421d657408167b1345188f8d
>> Author: Duncan Sands <baldrick at free.fr>
>> Date: Sun Feb 17 15:21:11 2013 +0000
>>
>> Use LLVMCC_EMITIR_FLAG rather than -emit-llvm
>>
>>
>> please review, looking forward to your feedback.
>>
>> thanks.
>>
>> ---
>> Regards,
>> Jiong
>> Tilera Corporation.
>>
>> _______________________________________________
>> LLVM Developers mailing list
>> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
>> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>>


-- 
Regards,
Jiong. Wang
Tilera Corporation.

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