[llvm-dev] Node deletion during DAG Combination ?

[Dominique Torette via llvm-dev]

Hi,

I'm trying to optimize the 'extract_vector_elt' for my SIMD microcontroller.
The idea is, during DAG combination, to merge load/extract sequence into an architecture specific node.
During Instruction Selection, this specific node will be target selected to an architecture specific instruction.
By 'combination of DAG nodes' I understand 'replacing a set of DAG nodes by an (usually smaller) set of DAG nodes, removing dead nodes and updating all the chains'.

I'm using the setTargetDAGCombine(ISD::EXTRACT_VECTOR_ELT) and build the new LOAD_VECTOR_EXTRACT node in the PerformDAGCombine().

As per the following trace this work, t59 and params from t58 are merged into t72.
During this combination, the chain from t59 to t58 has been merged from new t72 to t57, skipping over t58.
So far, so good.

My problem is that this node t58 is not removed from DAG. One reason could be that node t62 is still chained to t58 (due to the fact the extract_vector_elt has no chain).
(I also have to investigate why the t57 and t58 are duplicated... This should be another problem).

I've take a look at other DAGCombine implementation for others architecture but I didn't found an API to explicitly remove a node and trigger overall chain update.
Could someone point out an example of API for such node deletion during DAG Combination?

Regards, Dominique T.


      t56: ch = store<Volatile ST8[%l2]> t54:1, t55, FrameIndex:i16<1>, undef:i16
    t57: v2f32,ch = load<Volatile LD8[%l1]> t56, FrameIndex:i16<0>, undef:i16
  t58: v2f32,ch = load<Volatile LD8[%l1]> t57:1, FrameIndex:i16<0>, undef:i16
                    t59: f32 = extract_vector_elt t58, Constant:i16<0>
                  t62: ch = llvm.clp.writeapb.f32 t58:1, TargetConstant:i16<397>, Constant:i32<24575>, t59

Combining: t59: f32 = extract_vector_elt t58, Constant:i16<0>
... into: t72: f32 = CLPISD::LOAD_VECTOR_EXTRACT_o t57:1, FrameIndex:i16<0>, Constant:i16<0>

Combining: t56: ch = store<Volatile ST8[%l2]> t54:1, t55, FrameIndex:i16<1>, undef:i16
... into: t73: ch = CLPISD::STORE_VECTOR_INSERT_oo t53:1, FrameIndex:i16<1>, t53, Constant:i16<1>

    t73: ch = CLPISD::STORE_VECTOR_INSERT_oo t53:1, FrameIndex:i16<1>, t53, Constant:i16<1>
  t57: v2f32,ch = load<Volatile LD8[%l1]> t73, FrameIndex:i16<0>, undef:i16
                    t58: v2f32,ch = load<Volatile LD8[%l1]> t57:1, FrameIndex:i16<0>, undef:i16
                    t72: f32 = CLPISD::LOAD_VECTOR_EXTRACT_o t57:1, FrameIndex:i16<0>, Constant:i16<0>
                  t62: ch = llvm.clp.writeapb.f32 t58:1, TargetConstant:i16<397>, Constant:i32<24575>, t72

    t73: ch = MOVATO_B_oo t53, TargetFrameIndex:i16<1>, t53:1
  t57: v2f32,ch = LOAD_AB_o TargetFrameIndex:i16<0>, t73
  t58: v2f32,ch = LOAD_AB_o TargetFrameIndex:i16<0>, t57:1
                    t61: i32,ch = LOAD_A_i TargetConstant:i32<24575>, t58:1
                    t72: f32 = LOAD_A_o TargetFrameIndex:i16<0>, t57:1
                  t62: ch = WRITEAPB_A_oo t61, t72, t58:1








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Dominique Torette
System Architect
Rue des Chasseurs Ardennais - Liège Science Park - B-4031 Angleur
Tel: +32 (0) 4 361 81 11 - Fax: +32 (0) 4 361 81 20
www.spacebel.be<http://www.spacebel.be/>



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