[DAGCombine] Support splat_vector nodes in (and (extload)) dagcombine

llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

if ((N0.getOpcode() == ISD::EXTRACT_VECTOR_ELT &&
       (N0.getOpcode() == ISD::LOAD && N0.getResNo() == 0)) {
     LoadSDNode *Load = cast<LoadSDNode>( (N0.getOpcode() == ISD::LOAD) ?
                                          N0 : N0.getOperand(0) );
 
     // Get the constant (if applicable) the zero'th operand is being ANDed with.
     // This can be a pure constant or a vector splat, in which case we treat the
     // vector as a scalar and use the splat value.
     APInt Constant = APInt::getZero(1);
-    if (const ConstantSDNode *C = dyn_cast<ConstantSDNode>(N1)) {
+    if (const ConstantSDNode *C = isConstOrConstSplat(N1)) {
       Constant = C->getAPIntValue();
     } else if (BuildVectorSDNode *Vector = dyn_cast<BuildVectorSDNode>(N1)) {
       APInt SplatValue, SplatUndef;
       unsigned SplatBitSize;
       bool HasAnyUndefs;
       bool IsSplat = Vector->isConstantSplat(SplatValue, SplatUndef,
                                              SplatBitSize, HasAnyUndefs);
       if (IsSplat) {

llvm/test/CodeGen/AArch64/sve-fold-loadext-and-splat-vector.ll

+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc < %s | FileCheck %s
+
+target triple = "aarch64-unknown-linux-gnu"
+
+; Ensure that a no-op 'and' after an extending load gets removed when the and is
+; constructed via a splat_vector node.
+define <vscale x 2 x i64> @fold_loadext_and(ptr %ptr, i32 %needle, <vscale x 2 x i64> %b) #0 {
+; CHECK-LABEL: fold_loadext_and:
+; CHECK:       // %bb.0:
+; CHECK-NEXT:    ptrue p0.d
+; CHECK-NEXT:    ld1w { z0.d }, p0/z, [x0]
+; CHECK-NEXT:    ret
+  %load = load <vscale x 2 x i32>, ptr %ptr, align 4
+  %ext = zext <vscale x 2 x i32> %load to <vscale x 2 x i64>
+  %splatinsert = insertelement <vscale x 2 x i64> poison, i64 4294967295, i64 0
+  %splat = shufflevector <vscale x 2 x i64> %splatinsert, <vscale x 2 x i64> poison, <vscale x 2 x i32> zeroinitializer
+  %and = and <vscale x 2 x i64> %ext, %splat
+  ret <vscale x 2 x i64> %and
+}
+
+; Same as above but testing the case we care about. Here the vscale x 2 x i32
+; types get legalized into vscale x 2 x i64 types which introduces the extending
+; load and 'and' nodes similar to the above case.
+define <vscale x 2 x i1> @fold_loadext_and_legalize(ptr %ptr, <vscale x 2 x i32> %a) #0 {
+; CHECK-LABEL: fold_loadext_and_legalize:
+; CHECK:       // %bb.0:
+; CHECK-NEXT:    ptrue p0.d
+; CHECK-NEXT:    and z0.d, z0.d, #0xffffffff
+; CHECK-NEXT:    ld1w { z1.d }, p0/z, [x0]
+; CHECK-NEXT:    cmpeq p0.d, p0/z, z1.d, z0.d
+; CHECK-NEXT:    ret
+  %load = load <vscale x 2 x i32>, ptr %ptr
+  %cmp = icmp eq <vscale x 2 x i32> %load, %a
+  ret <vscale x 2 x i1> %cmp
+}
+
+attributes #0 = { "target-features"="+sve" }