This is an archive of the discontinued LLVM Phabricator instance.

[SVE][CGBuiltins] Remove need for instcombine from ACLE tests.
ClosedPublic

Authored by paulwalker-arm on Jan 5 2023, 7:20 AM.

Details

Summary

The SVE builtins tests rely on optimisations to remove clutter from
the resulting IR that is not relevant to the tests. However, with
the increasing number of target intrinsic combines the clang tests
are moving further away from verifying what is relevant to clang.

During early SVE (or rather scalable vector) bringup, we chose to
mitigate bugs by minimising our usage of LLVM IR instructions then
later implemented the combines to lower the calls to generic IR once
scalable vector support had matured. With the mitigations no longer
required and the combines mostly trivial I have moved the logic into
CGBuiltins, which allows the existing tests to remain unchanged once
they stop using instcombine.

The optimisations include:

  • Using shifts in place of multiplies by power-of-two values.
  • Don't emit getelementptrs when offset is zero.
  • Use IR based vector splats rather than calls to dup_x.
  • Use IR based vector selects rather than calls to sel.
  • Use i64 based indices for insertelement.

The test changes are the result of "sed -i -e 's/instcombine,//'",
with the exception of acle_sve_dupq.c which required regeneration
due to its previous reliance on a zext->tunc->zext combine.

The following tests still rely on instcombine because they require
changes beyond CGBuiltin.cpp:

CodeGen/aarch64-sve-intrinsics/acle_sve_clasta.c
CodeGen/aarch64-sve-intrinsics/acle_sve_clastb.c
CodeGen/aarch64-sve-intrinsics/acle_sve_cntb.c
CodeGen/aarch64-sve-intrinsics/acle_sve_cntd.c
CodeGen/aarch64-sve-intrinsics/acle_sve_cnth.c
CodeGen/aarch64-sve-intrinsics/acle_sve_cntw.c
CodeGen/aarch64-sve-intrinsics/acle_sve_dup-bfloat.c
CodeGen/aarch64-sve-intrinsics/acle_sve_dup.c
CodeGen/aarch64-sve-intrinsics/acle_sve_ld1-bfloat.c
CodeGen/aarch64-sve-intrinsics/acle_sve_ld1.c
CodeGen/aarch64-sve-intrinsics/acle_sve_ld1sb.c
CodeGen/aarch64-sve-intrinsics/acle_sve_ld1sh.c
CodeGen/aarch64-sve-intrinsics/acle_sve_ld1sw.c
CodeGen/aarch64-sve-intrinsics/acle_sve_ld1ub.c
CodeGen/aarch64-sve-intrinsics/acle_sve_ld1uh.c
CodeGen/aarch64-sve-intrinsics/acle_sve_ld1uw.c
CodeGen/aarch64-sve-intrinsics/acle_sve_len-bfloat.c
CodeGen/aarch64-sve-intrinsics/acle_sve_len.c
CodeGen/aarch64-sve-intrinsics/acle_sve_rdffr.c
CodeGen/aarch64-sve-intrinsics/acle_sve_sel-bfloat.c
CodeGen/aarch64-sve-intrinsics/acle_sve_sel.c
CodeGen/aarch64-sve-intrinsics/acle_sve_st1-bfloat.c
CodeGen/aarch64-sve-intrinsics/acle_sve_st1.c
CodeGen/aarch64-sve-intrinsics/acle_sve_st1b.c
CodeGen/aarch64-sve-intrinsics/acle_sve_st1h.c
CodeGen/aarch64-sve-intrinsics/acle_sve_st1w.c

Tests within aarch64-sve2-intrinsics don't use opt but instead use
-O1 to cleanup their output. These tests remain unchanged and will
be visited by a later patch.

Depends on D140983

Diff Detail

Event Timeline

paulwalker-arm created this revision.Jan 5 2023, 7:20 AM
Herald added a project: Restricted Project. · View Herald Transcript
paulwalker-arm requested review of this revision.Jan 5 2023, 7:20 AM
Herald added a project: Restricted Project. · View Herald TranscriptJan 5 2023, 7:20 AM
Matt added a subscriber: Matt.Jan 6 2023, 12:16 PM
david-arm added inline comments.Jan 11 2023, 1:59 AM
clang/lib/CodeGen/CGBuiltin.cpp
9092

Given this seems a frequent idiom is it worth putting this into a helper routine? i.e. something like

Ops[2] = getScaledOffset(Ops[2], BytesPerElt);

where

Value *getScaledOffset(SDValue Offset, unsigned Bytes) {
  Value *Scale = ConstantInt::get(Int64Ty, Log2_32(Bytes));
  return Builder.CreateShl(Offset, Scale);
}

Rebase and use simpler IRBuilder interface.

paulwalker-arm marked an inline comment as done.Jan 11 2023, 4:25 PM
paulwalker-arm added inline comments.
clang/lib/CodeGen/CGBuiltin.cpp
9092

Thanks Dave. It turns out IRBuilder has such a helper (well almost) function so I've used that instead.

david-arm accepted this revision.Jan 12 2023, 1:00 AM

LGTM! Thanks for making the changes @paulwalker-arm. :)

This revision is now accepted and ready to land.Jan 12 2023, 1:00 AM
This revision was automatically updated to reflect the committed changes.
paulwalker-arm marked an inline comment as done.

I removed -O1 from clang sve tests a while ago. The intent was always to remove instcombine and tailcallelim too, but I never got around to it. Feel free to remove -O1 from the other sve2 tests too, they ideally shouldn't test the entire pipeline from clang.