DAG: Add assert to getNode for EXTRACT_SUBVECTOR indexes (#154099)

Verify it's a multiple of the result vector element count
instead of asserting this in random combines.

The testcase in #153808 fails in the wrong point. Add an
assert to getNode so the invalid extract asserts at construction
instead of use.

Author: arsenm

llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

@@ -26097,8 +26097,6 @@ SDValue DAGCombiner::visitEXTRACT_SUBVECTOR(SDNode *N) {
     EVT ConcatSrcVT = V.getOperand(0).getValueType();
     assert(ConcatSrcVT.getVectorElementType() == NVT.getVectorElementType() &&
            "Concat and extract subvector do not change element type");
-    assert((ExtIdx % ExtNumElts) == 0 &&
-           "Extract index is not a multiple of the input vector length.");
 
     unsigned ConcatSrcNumElts = ConcatSrcVT.getVectorMinNumElements();
     unsigned ConcatOpIdx = ExtIdx / ConcatSrcNumElts;

llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp

@@ -7960,6 +7960,8 @@ SDValue SelectionDAG::getNode(unsigned Opcode, const SDLoc &DL, EVT VT,
     assert(N2C->getAPIntValue().getBitWidth() ==
                TLI->getVectorIdxWidth(getDataLayout()) &&
            "Constant index for EXTRACT_SUBVECTOR has an invalid size");
+    assert(N2C->getZExtValue() % VT.getVectorMinNumElements() == 0 &&
+           "Extract index is not a multiple of the output vector length");
 
     // Trivial extraction.
     if (VT == N1VT)