[llvm] [AArch64][GlobalISel] Combine Shuffles of G_CONCAT_VECTORS (PR #87489)

via llvm-commits llvm-commits at lists.llvm.org
Fri Apr 5 12:01:20 PDT 2024


llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-backend-aarch64

@llvm/pr-subscribers-llvm-globalisel

Author: None (chuongg3)

<details>
<summary>Changes</summary>

Combines G_SHUFFLE_VECTOR whose sources comes from G_CONCAT_VECTORS into a single G_CONCAT_VECTORS instruction. 

`// a = G_CONCAT_VECTORS x, y, undef, undef
// b = G_CONCAT_VECTORS z, undef, undef, undef
// c = G_SHUFFLE_VECTORS a, b, <0, 1, 4, undef>
// ===>
// c = G_CONCAT_VECTORS x, y, z, undef`

The first pre-commit comes from https://github.com/llvm/llvm-project/pull/85047

---
Full diff: https://github.com/llvm/llvm-project/pull/87489.diff


4 Files Affected:

- (modified) llvm/include/llvm/CodeGen/GlobalISel/CombinerHelper.h (+5) 
- (modified) llvm/include/llvm/Target/GlobalISel/Combine.td (+15-1) 
- (modified) llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp (+73) 
- (added) llvm/test/CodeGen/AArch64/GlobalISel/combine-shufflevector.mir (+202) 


``````````diff
diff --git a/llvm/include/llvm/CodeGen/GlobalISel/CombinerHelper.h b/llvm/include/llvm/CodeGen/GlobalISel/CombinerHelper.h
index 3af32043391fec..4b8aec8e8a5dd6 100644
--- a/llvm/include/llvm/CodeGen/GlobalISel/CombinerHelper.h
+++ b/llvm/include/llvm/CodeGen/GlobalISel/CombinerHelper.h
@@ -237,6 +237,11 @@ class CombinerHelper {
   /// or an implicit_def if \p Ops is empty.
   void applyCombineConcatVectors(MachineInstr &MI, SmallVector<Register> &Ops);
 
+  bool matchCombineShuffleConcat(MachineInstr &MI, SmallVector<Register> &Ops);
+  /// Replace \p MI with a flattened build_vector with \p Ops
+  /// or an implicit_def if \p Ops is empty.
+  void applyCombineShuffleConcat(MachineInstr &MI, SmallVector<Register> &Ops);
+
   /// Try to combine G_SHUFFLE_VECTOR into G_CONCAT_VECTORS.
   /// Returns true if MI changed.
   ///
diff --git a/llvm/include/llvm/Target/GlobalISel/Combine.td b/llvm/include/llvm/Target/GlobalISel/Combine.td
index 778ff7e437eb50..8401e48c1bc9eb 100644
--- a/llvm/include/llvm/Target/GlobalISel/Combine.td
+++ b/llvm/include/llvm/Target/GlobalISel/Combine.td
@@ -1507,6 +1507,18 @@ def combine_concat_vector : GICombineRule<
         [{ return Helper.matchCombineConcatVectors(*${root}, ${matchinfo}); }]),
   (apply [{ Helper.applyCombineConcatVectors(*${root}, ${matchinfo}); }])>;
 
+// Combines Shuffles of Concats
+// a = G_CONCAT_VECTORS x, y, undef, undef
+// b = G_CONCAT_VECTORS z, undef, undef, undef
+// c = G_SHUFFLE_VECTORS a, b, <0, 1, 4, undef>
+// ===>
+// c = G_CONCAT_VECTORS x, y, z, undef
+def combine_shuffle_concat : GICombineRule<
+  (defs root:$root, concat_matchinfo:$matchinfo),
+  (match (wip_match_opcode G_SHUFFLE_VECTOR):$root,
+        [{ return Helper.matchCombineShuffleConcat(*${root}, ${matchinfo}); }]),
+  (apply [{ Helper.applyCombineShuffleConcat(*${root}, ${matchinfo}); }])>;
+
 // match_extract_of_element must be the first!
 def vector_ops_combines: GICombineGroup<[
 match_extract_of_element_undef_vector,
@@ -1538,6 +1550,7 @@ extract_vector_element_build_vector_trunc8,
 extract_vector_element_freeze
 ]>;
 
+
 // FIXME: These should use the custom predicate feature once it lands.
 def undef_combines : GICombineGroup<[undef_to_fp_zero, undef_to_int_zero,
                                      undef_to_negative_one,
@@ -1614,7 +1627,8 @@ def all_combines : GICombineGroup<[trivial_combines, vector_ops_combines,
     and_or_disjoint_mask, fma_combines, fold_binop_into_select,
     sub_add_reg, select_to_minmax, redundant_binop_in_equality,
     fsub_to_fneg, commute_constant_to_rhs, match_ands, match_ors,
-    combine_concat_vector, double_icmp_zero_and_or_combine, match_addos]>;
+    combine_concat_vector, double_icmp_zero_and_or_combine, match_addos,
+    combine_shuffle_concat]>;
 
 // A combine group used to for prelegalizer combiners at -O0. The combines in
 // this group have been selected based on experiments to balance code size and
diff --git a/llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp b/llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp
index 719209e0edd5fb..9c18e0f136b715 100644
--- a/llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp
+++ b/llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp
@@ -303,6 +303,79 @@ void CombinerHelper::applyCombineConcatVectors(MachineInstr &MI,
   replaceRegWith(MRI, DstReg, NewDstReg);
 }
 
+bool CombinerHelper::matchCombineShuffleConcat(MachineInstr &MI,
+                                               SmallVector<Register> &Ops) {
+  ArrayRef<int> Mask = MI.getOperand(3).getShuffleMask();
+  auto ConcatMI1 = dyn_cast<GConcatVectors>(
+      getDefIgnoringCopies(MI.getOperand(1).getReg(), MRI));
+  auto ConcatMI2 = dyn_cast<GConcatVectors>(
+      getDefIgnoringCopies(MI.getOperand(2).getReg(), MRI));
+  if (!ConcatMI1 || !ConcatMI2)
+    return false;
+
+  // Check that the sources of the Concat instructions have the same type
+  if (MRI.getType(ConcatMI1->getSourceReg(0)) !=
+      MRI.getType(ConcatMI2->getSourceReg(0)))
+    return false;
+
+  LLT ConcatSrcTy = MRI.getType(ConcatMI1->getReg(1));
+  LLT ShuffleSrcTy1 = MRI.getType(MI.getOperand(1).getReg());
+  unsigned ConcatSrcNumElt = ConcatSrcTy.getNumElements();
+  for (unsigned i = 0; i < Mask.size(); i += ConcatSrcNumElt) {
+    // Check if the index takes a whole source register from G_CONCAT_VECTORS
+    // Assumes that all Sources of G_CONCAT_VECTORS are the same type
+    if (Mask[i] == -1) {
+      for (unsigned j = 1; j < ConcatSrcNumElt; j++) {
+        if (i + j >= Mask.size())
+          return false;
+        if (Mask[i + j] != -1)
+          return false;
+      }
+      Ops.push_back(0);
+    } else if (Mask[i] % (int)ConcatSrcNumElt == 0) {
+      for (unsigned j = 1; j < ConcatSrcNumElt; j++) {
+        if (i + j >= Mask.size())
+          return false;
+        if (Mask[i + j] != Mask[i] + (int)j)
+          return false;
+      }
+      // Retrieve the source register from its respective G_CONCAT_VECTORS
+      // instruction
+      if (Mask[i] < (int)ShuffleSrcTy1.getNumElements()) {
+        Ops.push_back(ConcatMI1->getSourceReg(Mask[i] / (int)ConcatSrcNumElt));
+      } else {
+        Ops.push_back(ConcatMI2->getSourceReg(Mask[i] / (int)ConcatSrcNumElt -
+                                              (int)ConcatMI1->getNumSources()));
+      }
+    } else {
+      return false;
+    }
+  }
+
+  if (Ops.size() == 0)
+    return false;
+  // Only deal with cases where G_CONCAT_VECTORS sources are all the same type
+  if ((Mask.size() - (Ops.size() * ConcatSrcNumElt)) %
+          MRI.getType(Ops[0]).getNumElements() !=
+      0)
+    return false;
+  return true;
+}
+
+void CombinerHelper::applyCombineShuffleConcat(MachineInstr &MI,
+                                               SmallVector<Register> &Ops) {
+  LLT SrcTy = MRI.getType(Ops[0]);
+  Register UndefReg = Builder.buildUndef(SrcTy).getReg(0);
+
+  for (unsigned i = 0; i < Ops.size(); i++) {
+    if (Ops[i] == 0)
+      Ops[i] = UndefReg;
+  }
+
+  Builder.buildConcatVectors(MI.getOperand(0).getReg(), Ops);
+  MI.eraseFromParent();
+}
+
 bool CombinerHelper::tryCombineShuffleVector(MachineInstr &MI) {
   SmallVector<Register, 4> Ops;
   if (matchCombineShuffleVector(MI, Ops)) {
diff --git a/llvm/test/CodeGen/AArch64/GlobalISel/combine-shufflevector.mir b/llvm/test/CodeGen/AArch64/GlobalISel/combine-shufflevector.mir
new file mode 100644
index 00000000000000..0de989f8be75d7
--- /dev/null
+++ b/llvm/test/CodeGen/AArch64/GlobalISel/combine-shufflevector.mir
@@ -0,0 +1,202 @@
+# NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py UTC_ARGS: --version 4
+# RUN: llc -o - -mtriple=aarch64-unknown-unknown -run-pass=aarch64-prelegalizer-combiner -verify-machineinstrs %s | FileCheck %s
+
+---
+name:            shuffle_concat_1
+tracksRegLiveness: true
+body:             |
+  bb.0:
+    liveins: $x0, $x1, $x2, $x3
+
+    ; CHECK-LABEL: name: shuffle_concat_1
+    ; CHECK: liveins: $x0, $x1, $x2, $x3
+    ; CHECK-NEXT: {{  $}}
+    ; CHECK-NEXT: %p2:_(p0) = COPY $x1
+    ; CHECK-NEXT: %p3:_(p0) = COPY $x2
+    ; CHECK-NEXT: %p4:_(p0) = COPY $x3
+    ; CHECK-NEXT: %a:_(<4 x s8>) = G_LOAD %p4(p0) :: (load (<4 x s8>))
+    ; CHECK-NEXT: %b:_(<4 x s8>) = G_LOAD %p3(p0) :: (load (<4 x s8>))
+    ; CHECK-NEXT: %c:_(<4 x s8>) = G_LOAD %p2(p0) :: (load (<4 x s8>))
+    ; CHECK-NEXT: [[DEF:%[0-9]+]]:_(<4 x s8>) = G_IMPLICIT_DEF
+    ; CHECK-NEXT: %z:_(<16 x s8>) = G_CONCAT_VECTORS %a(<4 x s8>), %b(<4 x s8>), %c(<4 x s8>), [[DEF]](<4 x s8>)
+    ; CHECK-NEXT: $q0 = COPY %z(<16 x s8>)
+    ; CHECK-NEXT: RET_ReallyLR implicit $q0
+    %p1:_(p0) = COPY $x0
+    %p2:_(p0) = COPY $x1
+    %p3:_(p0) = COPY $x2
+    %p4:_(p0) = COPY $x3
+
+    %ImpDef:_(<4 x s8>) = G_IMPLICIT_DEF
+    %a:_(<4 x s8>) = G_LOAD %p4:_(p0) :: (load (<4 x s8>))
+    %b:_(<4 x s8>) = G_LOAD %p3:_(p0) :: (load (<4 x s8>))
+    %c:_(<4 x s8>) = G_LOAD %p2:_(p0) :: (load (<4 x s8>))
+    %d:_(<4 x s8>) = G_LOAD %p1:_(p0) :: (load (<4 x s8>))
+
+    %x:_(<16 x s8>) = G_SHUFFLE_VECTOR %a:_(<4 x s8>), %b:_, shufflemask(0, 1, 2, 3, 4, 5, 6, 7, undef, undef, undef, undef, undef, undef, undef, undef)
+    %y:_(<16 x s8>) = G_SHUFFLE_VECTOR %c:_(<4 x s8>), %d:_, shufflemask(0, 1, 2, 3, undef, undef, undef, undef, undef, undef, undef, undef, undef, undef, undef, undef)
+    %z:_(<16 x s8>) = G_SHUFFLE_VECTOR %x:_(<16 x s8>), %y:_, shufflemask(0, 1, 2, 3, 4, 5, 6, 7, 16, 17, 18, 19, -1, -1, -1, -1)
+
+    $q0 = COPY %z(<16 x s8>)
+    RET_ReallyLR implicit $q0
+...
+
+---
+name:            shuffle_concat_2
+tracksRegLiveness: true
+body:             |
+  bb.0:
+    liveins: $x0, $x1, $x2, $x3
+
+    ; CHECK-LABEL: name: shuffle_concat_2
+    ; CHECK: liveins: $x0, $x1, $x2, $x3
+    ; CHECK-NEXT: {{  $}}
+    ; CHECK-NEXT: %p1:_(p0) = COPY $x0
+    ; CHECK-NEXT: %p2:_(p0) = COPY $x1
+    ; CHECK-NEXT: %p3:_(p0) = COPY $x2
+    ; CHECK-NEXT: %p4:_(p0) = COPY $x3
+    ; CHECK-NEXT: %a:_(<4 x s8>) = G_LOAD %p4(p0) :: (load (<4 x s8>))
+    ; CHECK-NEXT: %b:_(<4 x s8>) = G_LOAD %p3(p0) :: (load (<4 x s8>))
+    ; CHECK-NEXT: %c:_(<4 x s8>) = G_LOAD %p2(p0) :: (load (<4 x s8>))
+    ; CHECK-NEXT: %d:_(<4 x s8>) = G_LOAD %p1(p0) :: (load (<4 x s8>))
+    ; CHECK-NEXT: %z:_(<16 x s8>) = G_CONCAT_VECTORS %a(<4 x s8>), %b(<4 x s8>), %c(<4 x s8>), %d(<4 x s8>)
+    ; CHECK-NEXT: $q0 = COPY %z(<16 x s8>)
+    ; CHECK-NEXT: RET_ReallyLR implicit $q0
+    %p1:_(p0) = COPY $x0
+    %p2:_(p0) = COPY $x1
+    %p3:_(p0) = COPY $x2
+    %p4:_(p0) = COPY $x3
+
+    %ImpDef:_(<4 x s8>) = G_IMPLICIT_DEF
+    %a:_(<4 x s8>) = G_LOAD %p4:_(p0) :: (load (<4 x s8>))
+    %b:_(<4 x s8>) = G_LOAD %p3:_(p0) :: (load (<4 x s8>))
+    %c:_(<4 x s8>) = G_LOAD %p2:_(p0) :: (load (<4 x s8>))
+    %d:_(<4 x s8>) = G_LOAD %p1:_(p0) :: (load (<4 x s8>))
+
+    %v:_(<16 x s8>) = G_SHUFFLE_VECTOR %a:_(<4 x s8>), %b:_, shufflemask(0, 1, 2, 3, 4, 5, 6, 7, undef, undef, undef, undef, undef, undef, undef, undef)
+    %w:_(<16 x s8>) = G_SHUFFLE_VECTOR %c:_(<4 x s8>), %ImpDef:_, shufflemask(0, 1, 2, 3, undef, undef, undef, undef, undef, undef, undef, undef, undef, undef, undef, undef)
+    %x:_(<16 x s8>) = G_SHUFFLE_VECTOR %v:_(<16 x s8>), %w:_, shufflemask(0, 1, 2, 3, 4, 5, 6, 7, 16, 17, 18, 19, undef, undef, undef, undef)
+    %y:_(<16 x s8>) = G_SHUFFLE_VECTOR %d:_(<4 x s8>), %ImpDef:_, shufflemask(0, 1, 2, 3, undef, undef, undef, undef, undef, undef, undef, undef, undef, undef, undef, undef)
+    %z:_(<16 x s8>) = G_SHUFFLE_VECTOR %x:_(<16 x s8>), %y:_, shufflemask(0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 16, 17, 18, 19)
+
+    $q0 = COPY %z(<16 x s8>)
+    RET_ReallyLR implicit $q0
+...
+
+---
+name:            shuffle_concat_3
+tracksRegLiveness: true
+body:             |
+  bb.0:
+    liveins: $x0, $x1, $x2, $x3
+
+    ; CHECK-LABEL: name: shuffle_concat_3
+    ; CHECK: liveins: $x0, $x1, $x2, $x3
+    ; CHECK-NEXT: {{  $}}
+    ; CHECK-NEXT: %p2:_(p0) = COPY $x1
+    ; CHECK-NEXT: %p3:_(p0) = COPY $x2
+    ; CHECK-NEXT: %p4:_(p0) = COPY $x3
+    ; CHECK-NEXT: %a:_(<4 x s8>) = G_LOAD %p4(p0) :: (load (<4 x s8>))
+    ; CHECK-NEXT: %b:_(<4 x s8>) = G_LOAD %p3(p0) :: (load (<4 x s8>))
+    ; CHECK-NEXT: %c:_(<4 x s8>) = G_LOAD %p2(p0) :: (load (<4 x s8>))
+    ; CHECK-NEXT: [[DEF:%[0-9]+]]:_(<4 x s8>) = G_IMPLICIT_DEF
+    ; CHECK-NEXT: [[CONCAT_VECTORS:%[0-9]+]]:_(<16 x s8>) = G_CONCAT_VECTORS %a(<4 x s8>), %b(<4 x s8>), [[DEF]](<4 x s8>), [[DEF]](<4 x s8>)
+    ; CHECK-NEXT: [[CONCAT_VECTORS1:%[0-9]+]]:_(<16 x s8>) = G_CONCAT_VECTORS %c(<4 x s8>), [[DEF]](<4 x s8>), [[DEF]](<4 x s8>), [[DEF]](<4 x s8>)
+    ; CHECK-NEXT: %z:_(<16 x s8>) = G_SHUFFLE_VECTOR [[CONCAT_VECTORS]](<16 x s8>), [[CONCAT_VECTORS1]], shufflemask(0, undef, 2, 3, 4, 5, 6, 7, 16, 17, 18, 19, undef, undef, undef, undef)
+    ; CHECK-NEXT: $q0 = COPY %z(<16 x s8>)
+    ; CHECK-NEXT: RET_ReallyLR implicit $q0
+    %p1:_(p0) = COPY $x0
+    %p2:_(p0) = COPY $x1
+    %p3:_(p0) = COPY $x2
+    %p4:_(p0) = COPY $x3
+
+    %ImpDef:_(<4 x s8>) = G_IMPLICIT_DEF
+    %a:_(<4 x s8>) = G_LOAD %p4:_(p0) :: (load (<4 x s8>))
+    %b:_(<4 x s8>) = G_LOAD %p3:_(p0) :: (load (<4 x s8>))
+    %c:_(<4 x s8>) = G_LOAD %p2:_(p0) :: (load (<4 x s8>))
+    %d:_(<4 x s8>) = G_LOAD %p1:_(p0) :: (load (<4 x s8>))
+
+    %x:_(<16 x s8>) = G_SHUFFLE_VECTOR %a:_(<4 x s8>), %b:_, shufflemask(0, 1, 2, 3, 4, 5, 6, 7, undef, undef, undef, undef, undef, undef, undef, undef)
+    %y:_(<16 x s8>) = G_SHUFFLE_VECTOR %c:_(<4 x s8>), %d:_, shufflemask(0, 1, 2, 3, undef, undef, undef, undef, undef, undef, undef, undef, undef, undef, undef, undef)
+    %z:_(<16 x s8>) = G_SHUFFLE_VECTOR %x:_(<16 x s8>), %y:_, shufflemask(0, -1, 2, 3, 4, 5, 6, 7, 16, 17, 18, 19, -1, -1, -1, -1)
+
+    $q0 = COPY %z(<16 x s8>)
+    RET_ReallyLR implicit $q0
+...
+
+---
+name:            shuffle_concat_4
+tracksRegLiveness: true
+body:             |
+  bb.0:
+    liveins: $x0, $x1, $x2, $x3
+
+    ; CHECK-LABEL: name: shuffle_concat_4
+    ; CHECK: liveins: $x0, $x1, $x2, $x3
+    ; CHECK-NEXT: {{  $}}
+    ; CHECK-NEXT: %p2:_(p0) = COPY $x1
+    ; CHECK-NEXT: %p4:_(p0) = COPY $x3
+    ; CHECK-NEXT: %a:_(<4 x s8>) = G_LOAD %p4(p0) :: (load (<4 x s8>))
+    ; CHECK-NEXT: %c:_(<4 x s8>) = G_LOAD %p2(p0) :: (load (<4 x s8>))
+    ; CHECK-NEXT: [[DEF:%[0-9]+]]:_(<4 x s8>) = G_IMPLICIT_DEF
+    ; CHECK-NEXT: %z:_(<16 x s8>) = G_CONCAT_VECTORS %a(<4 x s8>), [[DEF]](<4 x s8>), %c(<4 x s8>), [[DEF]](<4 x s8>)
+    ; CHECK-NEXT: $q0 = COPY %z(<16 x s8>)
+    ; CHECK-NEXT: RET_ReallyLR implicit $q0
+    %p1:_(p0) = COPY $x0
+    %p2:_(p0) = COPY $x1
+    %p3:_(p0) = COPY $x2
+    %p4:_(p0) = COPY $x3
+
+    %ImpDef:_(<4 x s8>) = G_IMPLICIT_DEF
+    %a:_(<4 x s8>) = G_LOAD %p4:_(p0) :: (load (<4 x s8>))
+    %b:_(<4 x s8>) = G_LOAD %p3:_(p0) :: (load (<4 x s8>))
+    %c:_(<4 x s8>) = G_LOAD %p2:_(p0) :: (load (<4 x s8>))
+    %d:_(<4 x s8>) = G_LOAD %p1:_(p0) :: (load (<4 x s8>))
+
+    %x:_(<16 x s8>) = G_SHUFFLE_VECTOR %a:_(<4 x s8>), %b:_, shufflemask(0, 1, 2, 3, 4, 5, 6, 7, undef, undef, undef, undef, undef, undef, undef, undef)
+    %y:_(<16 x s8>) = G_SHUFFLE_VECTOR %c:_(<4 x s8>), %d:_, shufflemask(0, 1, 2, 3, undef, undef, undef, undef, undef, undef, undef, undef, undef, undef, undef, undef)
+    %z:_(<16 x s8>) = G_SHUFFLE_VECTOR %x:_(<16 x s8>), %y:_, shufflemask(0, 1, 2, 3, -1, -1, -1, -1, 16, 17, 18, 19, -1, -1, -1, -1)
+
+    $q0 = COPY %z(<16 x s8>)
+    RET_ReallyLR implicit $q0
+...
+
+---
+name:            shuffle_concat_5
+tracksRegLiveness: true
+body:             |
+  bb.0:
+    liveins: $x0, $x1, $x2, $x3
+
+    ; CHECK-LABEL: name: shuffle_concat_5
+    ; CHECK: liveins: $x0, $x1, $x2, $x3
+    ; CHECK-NEXT: {{  $}}
+    ; CHECK-NEXT: %p2:_(p0) = COPY $x1
+    ; CHECK-NEXT: %p3:_(p0) = COPY $x2
+    ; CHECK-NEXT: %p4:_(p0) = COPY $x3
+    ; CHECK-NEXT: %a:_(<4 x s8>) = G_LOAD %p4(p0) :: (load (<4 x s8>))
+    ; CHECK-NEXT: %b:_(<4 x s8>) = G_LOAD %p3(p0) :: (load (<4 x s8>))
+    ; CHECK-NEXT: %c:_(<4 x s8>) = G_LOAD %p2(p0) :: (load (<4 x s8>))
+    ; CHECK-NEXT: [[DEF:%[0-9]+]]:_(<4 x s8>) = G_IMPLICIT_DEF
+    ; CHECK-NEXT: [[CONCAT_VECTORS:%[0-9]+]]:_(<16 x s8>) = G_CONCAT_VECTORS %a(<4 x s8>), %b(<4 x s8>), [[DEF]](<4 x s8>), [[DEF]](<4 x s8>)
+    ; CHECK-NEXT: [[CONCAT_VECTORS1:%[0-9]+]]:_(<16 x s8>) = G_CONCAT_VECTORS %c(<4 x s8>), [[DEF]](<4 x s8>), [[DEF]](<4 x s8>), [[DEF]](<4 x s8>)
+    ; CHECK-NEXT: %z:_(<16 x s8>) = G_SHUFFLE_VECTOR [[CONCAT_VECTORS]](<16 x s8>), [[CONCAT_VECTORS1]], shufflemask(undef, 1, 2, 3, 4, 5, 6, 7, 16, 17, 18, 19, undef, undef, undef, undef)
+    ; CHECK-NEXT: $q0 = COPY %z(<16 x s8>)
+    ; CHECK-NEXT: RET_ReallyLR implicit $q0
+    %p1:_(p0) = COPY $x0
+    %p2:_(p0) = COPY $x1
+    %p3:_(p0) = COPY $x2
+    %p4:_(p0) = COPY $x3
+
+    %ImpDef:_(<4 x s8>) = G_IMPLICIT_DEF
+    %a:_(<4 x s8>) = G_LOAD %p4:_(p0) :: (load (<4 x s8>))
+    %b:_(<4 x s8>) = G_LOAD %p3:_(p0) :: (load (<4 x s8>))
+    %c:_(<4 x s8>) = G_LOAD %p2:_(p0) :: (load (<4 x s8>))
+    %d:_(<4 x s8>) = G_LOAD %p1:_(p0) :: (load (<4 x s8>))
+
+    %x:_(<16 x s8>) = G_SHUFFLE_VECTOR %a:_(<4 x s8>), %b:_, shufflemask(0, 1, 2, 3, 4, 5, 6, 7, undef, undef, undef, undef, undef, undef, undef, undef)
+    %y:_(<16 x s8>) = G_SHUFFLE_VECTOR %c:_(<4 x s8>), %d:_, shufflemask(0, 1, 2, 3, undef, undef, undef, undef, undef, undef, undef, undef, undef, undef, undef, undef)
+    %z:_(<16 x s8>) = G_SHUFFLE_VECTOR %x:_(<16 x s8>), %y:_, shufflemask(-1, 1, 2, 3, 4, 5, 6, 7, 16, 17, 18, 19, -1, -1, -1, -1)
+
+    $q0 = COPY %z(<16 x s8>)
+    RET_ReallyLR implicit $q0
+...

``````````

</details>


https://github.com/llvm/llvm-project/pull/87489


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