[clang] [llvm] [msan] Implement support for Arm NEON vst{2,3,4} instructions (PR #99360)

[Vitaly Buka via cfe-commits]

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@@ -3742,6 +3751,124 @@ struct MemorySanitizerVisitor : public InstVisitor<MemorySanitizerVisitor> {
     setOriginForNaryOp(I);
   }
 
+  // Given two shadows AAAA..., BBBB..., return the interleaved value
+  // ABABABAB ...
+  //
+  // Width == number of elements in A == number of elements in B
+  Value *interleaveAB(IRBuilder<> &IRB, Value *left, Value *right, uint Width) {
+    assert(isa<FixedVectorType>(left->getType()));
+    assert(isa<FixedVectorType>(right->getType()));
+    assert(cast<FixedVectorType>(left->getType())->getNumElements() == Width);
+    assert(cast<FixedVectorType>(right->getType())->getNumElements() == Width);
+
+    SmallVector<Constant *> Idxs;
+
+    for (uint i = 0; i < Width; i++) {
+      Idxs.push_back(IRB.getInt32(i));
+      Idxs.push_back(IRB.getInt32(i + Width));
+    }
+
+    return IRB.CreateShuffleVector(left, right, ConstantVector::get(Idxs));
+  }
+
+  // Given three shadows, which are already interleaved into two shadows
+  // ABABABAB and CxCxCxCx (x is undef), return the interleaved value ABCABCABC.
+  //
+  // Note: Width == number of elements in A == number of elements in B
+  //             == number of elements in C
+  Value *interleaveABCx(IRBuilder<> &IRB, Value *left, Value *right,
+                        uint Width) {
+    assert(isa<FixedVectorType>(left->getType()));
+    assert(isa<FixedVectorType>(right->getType()));
+    assert(cast<FixedVectorType>(left->getType())->getNumElements() == 2 * Width);
+    assert(cast<FixedVectorType>(right->getType())->getNumElements() == 2 * Width);
+
+    SmallVector<Constant *> Idxs;
+
+    // Width parameter is the width of a single shadow (e.g., A).
+    // The width of AB (or Cx) is Width * 2.
+    for (uint i = 0; i < Width * 2; i += 2) {
+      Idxs.push_back(IRB.getInt32(i));
+      Idxs.push_back(IRB.getInt32(i + 1));
+      Idxs.push_back(IRB.getInt32(i + Width));
+      // Index (i + 1 + Width) contains Undef; don't copy
+    }
+
+    return IRB.CreateShuffleVector(left, right, ConstantVector::get(Idxs));
+  }
+
+  /// Calculates the shadow for interleaving 2, 3 or 4 vectors
+  /// (e.g., for Arm NEON vector store).
+  Value *interleaveShadow(IRBuilder<> &IRB, IntrinsicInst &I) {
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vitalybuka wrote:

Another version of the instrumentation could be just clone instruction and use shadow values as arguments. It's probably OK here.

https://github.com/llvm/llvm-project/pull/99360