[PATCH] D93229: [VectorCombine] allow peeking through GEPs when creating a vector load

[Roman Lebedev via Phabricator via llvm-commits]

lebedev.ri requested changes to this revision.
lebedev.ri added subscribers: aqjune, nlopes.
lebedev.ri added a comment.
This revision now requires changes to proceed.

I'm having trouble coming up with an example because there appears to be a preexisting soundness problems, example: (CC @nlopes @aqjune)

  define <8 x i16> @t(i8* align 128 dereferenceable(128) %base) {
    %ptr = getelementptr inbounds i8, i8* %base, i64 1
    %p = bitcast i8* %ptr to <8 x i16>*
  
    %gep = getelementptr inbounds <8 x i16>, <8 x i16>* %p, i64 0, i64 1
    %s = load i16, i16* %gep, align 1
    %r = insertelement <8 x i16> undef, i16 %s, i64 0
    ret <8 x i16> %r
  }

  /builddirs/llvm-project/build-Clang11-unknown$ /builddirs/llvm-project/build-Clang11-unknown/bin/opt -load /repositories/alive2/build-Clang-release/tv/tv.so -tv -vector-combine -mtriple=x86_64-- -mattr=avx2 -tv -o /dev/null --tv-smt-to=60000 /tmp/D93229.ll 
  
  ----------------------------------------
  define <8 x i16> @t(* dereferenceable(128) align(128) %base) {
  %0:
    %ptr = gep inbounds * dereferenceable(128) align(128) %base, 1 x i64 1
    %p = bitcast * %ptr to *
    %gep = gep inbounds * %p, 16 x i64 0, 2 x i64 1
    %s = load i16, * %gep, align 1
    %r = insertelement <8 x i16> undef, i16 %s, i64 0
    ret <8 x i16> %r
  }
  =>
  define <8 x i16> @t(* dereferenceable(128) align(128) %base) {
  %0:
    %ptr = gep inbounds * dereferenceable(128) align(128) %base, 1 x i64 1
    %p = bitcast * %ptr to *
    %gep = gep inbounds * %p, 16 x i64 0, 2 x i64 1
    %1 = bitcast * %gep to *
    %r = load <8 x i16>, * %1, align 1
    ret <8 x i16> %r
  }
  Transformation doesn't verify!
  ERROR: Target is more poisonous than source
  
  Example:
  * dereferenceable(128) align(128) %base = pointer(non-local, block_id=1, offset=1664)
  
  Source:
  * %ptr = pointer(non-local, block_id=1, offset=1665)
  * %p = pointer(non-local, block_id=1, offset=1665)
  * %gep = pointer(non-local, block_id=1, offset=1667)
  i16 %s = poison
  <8 x i16> %r = < poison, any, any, any, any, any, any, any >
  
  SOURCE MEMORY STATE
  ===================
  NON-LOCAL BLOCKS:
  Block 0 >       size: 0 align: 1        alloc type: 0
  Block 1 >       size: 2048      align: 128      alloc type: 0
  
  Target:
  * %ptr = pointer(non-local, block_id=1, offset=1665)
  * %p = pointer(non-local, block_id=1, offset=1665)
  * %gep = pointer(non-local, block_id=1, offset=1667)
  * %1 = pointer(non-local, block_id=1, offset=1667)
  <8 x i16> %r = < poison, poison, poison, poison, poison, poison, poison, poison >
  Source value: < poison, any, any, any, any, any, any, any >
  Target value: < poison, poison, poison, poison, poison, poison, poison, poison >
  
  Alive2: Transform doesn't verify!




CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D93229/new/

https://reviews.llvm.org/D93229