[llvm] [InstCombine] Added pattern for recognising the construction of packed integers. (PR #147414)

[Yingwei Zheng via llvm-commits]

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@@ -3592,6 +3595,154 @@ static Value *foldOrOfInversions(BinaryOperator &I,
   return nullptr;
 }
 
+/// Match \p V as "shufflevector -> bitcast" or "extractelement -> zext -> shl"
+/// patterns, which extract vector elements and pack them in the same relative
+/// positions.
+///
+/// \p Vec is the underlying vector being extracted from.
+/// \p Mask is a bitmask identifying which packed elements are obtained from the
+/// vector.
+/// \p VecOffset is the vector element corresponding to index 0 of the
+/// mask.
+static bool matchSubIntegerPackFromVector(Value *V, Value *&Vec,
+                                          int64_t &VecOffset,
+                                          SmallBitVector &Mask,
+                                          const DataLayout &DL) {
+  static const auto m_ConstShlOrSelf = [](const auto &Base, uint64_t &ShlAmt) {
+    ShlAmt = 0;
+    return m_CombineOr(m_Shl(Base, m_ConstantInt(ShlAmt)), Base);
+  };
+
+  // First try to match extractelement -> zext -> shl
+  uint64_t VecIdx, ShlAmt;
+  if (match(V, m_ConstShlOrSelf(m_ZExtOrSelf(m_ExtractElt(
+                                    m_Value(Vec), m_ConstantInt(VecIdx))),
+                                ShlAmt))) {
+    auto *VecTy = dyn_cast<FixedVectorType>(Vec->getType());
+    if (!VecTy)
+      return false;
+    auto *EltTy = dyn_cast<IntegerType>(VecTy->getElementType());
+    if (!EltTy)
+      return false;
+
+    const unsigned EltBitWidth = EltTy->getBitWidth();
+    const unsigned TargetBitWidth = V->getType()->getIntegerBitWidth();
+    if (TargetBitWidth % EltBitWidth != 0 || ShlAmt % EltBitWidth != 0)
+      return false;
+    const unsigned TargetEltWidth = TargetBitWidth / EltBitWidth;
+    const unsigned ShlEltAmt = ShlAmt / EltBitWidth;
+
+    const unsigned MaskIdx =
+        DL.isLittleEndian() ? ShlEltAmt : TargetEltWidth - ShlEltAmt - 1;
+
+    VecOffset = static_cast<int64_t>(VecIdx) - static_cast<int64_t>(MaskIdx);
+    Mask.resize(TargetEltWidth);
+    Mask.set(MaskIdx);
+    return true;
+  }
+
+  // Now try to match a bitcasted subvector.
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dtcxzyw wrote:

Oops, I saw the test diff after commenting out the code below.

https://github.com/llvm/llvm-project/pull/147414