[llvm] [msan] Generalize handlePairwiseShadowOrIntrinsic, and handle x86 pairwise add/sub (PR #127567)

[Thurston Dang via llvm-commits]

================
@@ -2618,28 +2625,56 @@ struct MemorySanitizerVisitor : public InstVisitor<MemorySanitizerVisitor> {
     FixedVectorType *ParamType =
         cast<FixedVectorType>(I.getArgOperand(0)->getType());
     if (I.arg_size() == 2)
-      assert(ParamType == cast<FixedVectorType>(I.getArgOperand(1)->getType()));
+      assert(I.getArgOperand(0)->getType() == I.getArgOperand(1)->getType());
+
     [[maybe_unused]] FixedVectorType *ReturnType =
         cast<FixedVectorType>(I.getType());
     assert(ParamType->getNumElements() * I.arg_size() ==
            2 * ReturnType->getNumElements());
 
     IRBuilder<> IRB(&I);
-    unsigned Width = ParamType->getNumElements() * I.arg_size();
+
+    unsigned TotalNumElems = ParamType->getNumElements() * I.arg_size();
+    FixedVectorType *ReinterpretShadowTy = nullptr;
+    if (ReinterpretElemWidth.has_value()) {
+      assert(ParamType->getPrimitiveSizeInBits() %
+                 ReinterpretElemWidth.value() ==
+             0);
+      ReinterpretShadowTy = FixedVectorType::get(
+          IRB.getIntNTy(ReinterpretElemWidth.value()),
+          ParamType->getPrimitiveSizeInBits() / ReinterpretElemWidth.value());
+      TotalNumElems = ReinterpretShadowTy->getNumElements() * I.arg_size();
+    }
 
     // Horizontal OR of shadow
     SmallVector<int, 8> EvenMask;
     SmallVector<int, 8> OddMask;
-    for (unsigned X = 0; X < Width; X += 2) {
+    for (unsigned X = 0; X + 1 < TotalNumElems; X += 2) {
       EvenMask.push_back(X);
       OddMask.push_back(X + 1);
     }
 
     Value *FirstArgShadow = getShadow(&I, 0);
+    if (ReinterpretShadowTy)
+      FirstArgShadow = IRB.CreateBitCast(FirstArgShadow, ReinterpretShadowTy);
+
+    // If we had two parameters each with an odd number of elements, the total
+    // number of elements is even, but we have never seen this in extant
+    // instruction sets, so we enforce that each parameter must have an even
+    // number of elements.
+    assert(
+        (cast<FixedVectorType>(FirstArgShadow->getType())->getNumElements()) %
----------------
thurstond wrote:

Done. Note I used LLVM's isAligned because sanitizer_common isn't included in MemorySanitizer.cpp.

https://github.com/llvm/llvm-project/pull/127567