[llvm-dev] LLVM Backend Issues

Wed Jun 22 11:25:57 PDT 2016

Thanks Anton and Krzysztof!

Here is the dump using the -debug flag. At this point I am not making much
sense of this, would it be too much to ask if one of you could walk me
through one of these lines?

One thing that I didn't point out is that I never defined any separate
floating point registers, not sure if this will pose any issue?

Thanks again for your time!

Jeff

jeff at ubuntu:~/code$ llc -debug-only=isel dft_gf_msp.ll

=== main
Initial selection DAG: BB#0 'main:entry'
SelectionDAG has 18 nodes:
            t0: ch = EntryToken
          t4: ch = store<ST4[%retval]> t0, Constant:i32<0>,
FrameIndex:i32<0>, undef:i32
        t7: ch = store<ST4[%sz]> t4, Constant:i32<256>, FrameIndex:i32<2>,
undef:i32
      t10: ch = store<ST4[%dir]> t7, ConstantFP:f32<-1.000000e+00>,
FrameIndex:i32<3>, undef:i32
    t12: ch = store<ST4[%m]> t10, Constant:i32<0>, FrameIndex:i32<19>,
undef:i32
  t13: i32,ch = load<LD4[%sz]> t12, FrameIndex:i32<2>, undef:i32
    t15: ch = store<ST4[%j]> t13:1, t13, FrameIndex:i32<16>, undef:i32
  t17: ch = store<ST4[%le]> t15, t13, FrameIndex:i32<14>, undef:i32

Optimized lowered selection DAG: BB#0 'main:entry'
SelectionDAG has 18 nodes:
            t0: ch = EntryToken
          t4: ch = store<ST4[%retval]> t0, Constant:i32<0>,
FrameIndex:i32<0>, undef:i32
        t7: ch = store<ST4[%sz]> t4, Constant:i32<256>, FrameIndex:i32<2>,
undef:i32
      t19: ch = store<ST4[%dir]> t7, Constant:i32<-1082130432>,
FrameIndex:i32<3>, undef:i32
    t12: ch = store<ST4[%m]> t19, Constant:i32<0>, FrameIndex:i32<19>,
undef:i32
  t13: i32,ch = load<LD4[%sz]> t12, FrameIndex:i32<2>, undef:i32
    t15: ch = store<ST4[%j]> t13:1, t13, FrameIndex:i32<16>, undef:i32
  t17: ch = store<ST4[%le]> t15, t13, FrameIndex:i32<14>, undef:i32

Type-legalized selection DAG: BB#0 'main:entry'
SelectionDAG has 18 nodes:
            t0: ch = EntryToken
          t4: ch = store<ST4[%retval]> t0, Constant:i32<0>,
FrameIndex:i32<0>, undef:i32
        t7: ch = store<ST4[%sz]> t4, Constant:i32<256>, FrameIndex:i32<2>,
undef:i32
      t19: ch = store<ST4[%dir]> t7, Constant:i32<-1082130432>,
FrameIndex:i32<3>, undef:i32
    t12: ch = store<ST4[%m]> t19, Constant:i32<0>, FrameIndex:i32<19>,
undef:i32
  t13: i32,ch = load<LD4[%sz]> t12, FrameIndex:i32<2>, undef:i32
    t15: ch = store<ST4[%j]> t13:1, t13, FrameIndex:i32<16>, undef:i32
  t17: ch = store<ST4[%le]> t15, t13, FrameIndex:i32<14>, undef:i32

Legalized selection DAG: BB#0 'main:entry'
SelectionDAG has 18 nodes:
            t0: ch = EntryToken
          t4: ch = store<ST4[%retval]> t0, Constant:i32<0>,
FrameIndex:i32<0>, undef:i32
        t7: ch = store<ST4[%sz]> t4, Constant:i32<256>, FrameIndex:i32<2>,
undef:i32
      t19: ch = store<ST4[%dir]> t7, Constant:i32<-1082130432>,
FrameIndex:i32<3>, undef:i32
    t12: ch = store<ST4[%m]> t19, Constant:i32<0>, FrameIndex:i32<19>,
undef:i32
  t13: i32,ch = load<LD4[%sz]> t12, FrameIndex:i32<2>, undef:i32
    t15: ch = store<ST4[%j]> t13:1, t13, FrameIndex:i32<16>, undef:i32
  t17: ch = store<ST4[%le]> t15, t13, FrameIndex:i32<14>, undef:i32

Optimized legalized selection DAG: BB#0 'main:entry'
SelectionDAG has 18 nodes:
            t0: ch = EntryToken
          t4: ch = store<ST4[%retval]> t0, Constant:i32<0>,
FrameIndex:i32<0>, undef:i32
        t7: ch = store<ST4[%sz]> t4, Constant:i32<256>, FrameIndex:i32<2>,
undef:i32
      t19: ch = store<ST4[%dir]> t7, Constant:i32<-1082130432>,
FrameIndex:i32<3>, undef:i32
    t12: ch = store<ST4[%m]> t19, Constant:i32<0>, FrameIndex:i32<19>,
undef:i32
  t13: i32,ch = load<LD4[%sz]> t12, FrameIndex:i32<2>, undef:i32
    t15: ch = store<ST4[%j]> t13:1, t13, FrameIndex:i32<16>, undef:i32
  t17: ch = store<ST4[%le]> t15, t13, FrameIndex:i32<14>, undef:i32

===== Instruction selection begins: BB#0 'entry'
ISEL: Starting pattern match on root node: t17: ch = store<ST4[%le]> t15,
t13, FrameIndex:i32<14>, undef:i32

  Match failed at index 0
LLVM ERROR: Cannot select: t17: ch = store<ST4[%le]> t15, t13,
FrameIndex:i32<14>, undef:i32
  t13: i32,ch = load<LD4[%sz]> t12, FrameIndex:i32<2>, undef:i32
    t6: i32 = FrameIndex<2>
    t3: i32 = undef
  t16: i32 = FrameIndex<14>
  t3: i32 = undef
In function: main

On Tue, Jun 21, 2016 at 11:19 AM, Krzysztof Parzyszek via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> On 6/21/2016 11:12 AM, Jeff E via llvm-dev wrote:
>
>>
>> Also - It would be great if someone could point me to a document that
>> describes some of these error messages? For example what does t26 ..t4
>> mean?
>>
>
> The t.. are just identifiers of the DAG nodes. It used to print addresses,
> but they were long and would change every time.
>
> The "cannot select" errors are not that hard to track down: compile the
> failing testcase with -debug-only=isel and you'll see all the steps being
> taken up to the moment of failure.  The last few messages will be something
> like "match failed at nnn".  In your build directory in
> lib/Target/<yourtarget> there will be a file <yourtarget>GenDAGISel.inc.
> It contains the matching "script".  The numbers nnn are shown in comments
> in that file and correspond to the steps the matcher performs. You'll be
> able to see what exactly it's trying to match.
>
> -Krzysztof
>
>
> --
> Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted
> by The Linux Foundation
>
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20160622/f6819562/attachment-0001.html>