[all-commits] [llvm/llvm-project] be6c8d: [SelectionDAG] Fix getVectorSubVecPointer for scal...

[sdesmalen-arm via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: be6c8dc765c32a79c0c9b0e6720e3b22d226e478
      https://github.com/llvm/llvm-project/commit/be6c8dc765c32a79c0c9b0e6720e3b22d226e478
  Author: Sander de Smalen <sander.desmalen at arm.com>
  Date:   2021-10-20 (Wed, 20 Oct 2021)

  Changed paths:
    M llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
    M llvm/test/CodeGen/AArch64/sve-insert-vector.ll

  Log Message:
  -----------
  [SelectionDAG] Fix getVectorSubVecPointer for scalable subvectors.

When inserting a scalable subvector into a scalable vector through
the stack, the index to store to needs to be scaled by vscale.
Before this patch, that didn't yet happen, so it would generate the
wrong offset, thus storing a subvector to the incorrect address
and overwriting the wrong lanes.

For some insert:
  nxv8f16 insert_subvector(nxv8f16 %vec, nxv2f16 %subvec, i64 2)

The offset was not scaled by vscale:
  orr     x8, x8, #0x4
  st1h    { z0.h }, p0, [sp]
  st1h    { z1.d }, p1, [x8]
  ld1h    { z0.h }, p0/z, [sp]

And is changed to:
  mov x8, sp
  st1h { z0.h }, p0, [sp]
  st1h { z1.d }, p1, [x8, #1, mul vl]
  ld1h { z0.h }, p0/z, [sp]

Differential Revision: https://reviews.llvm.org/D111633