[SelectionDAG] Replace the Chain in LOAD->VP_LOAD widening

[frasercrmck]

Summary

The introduction of this legalization, D111248, forgot to replace the
old chain with the new. This could manifest itself in the old
(illegally-typed) value remaining in the DAG, though the simple test
cases didn't catch this.

[craig.topper]

LGTM

llvm/lib/CodeGen/SelectionDAG/LegalizeVectorTypes.cpp

if (ExtType == ISD::NON_EXTLOAD && WideVT.isScalableVector() &&
       TLI.isTypeLegal(WideMaskVT)) {
     SDLoc DL(N);
     SDValue Mask = DAG.getAllOnesConstant(DL, WideMaskVT);
     MVT EVLVT = TLI.getVPExplicitVectorLengthTy();
     unsigned NumVTElts = LdVT.getVectorMinNumElements();
     SDValue EVL =
         DAG.getVScale(DL, EVLVT, APInt(EVLVT.getScalarSizeInBits(), NumVTElts));
     const auto *MMO = LD->getMemOperand();
-    return DAG.getLoadVP(WideVT, DL, LD->getChain(), LD->getBasePtr(), Mask,
-                         EVL, MMO->getPointerInfo(), MMO->getAlign(),
-                         MMO->getFlags(), MMO->getAAInfo());
+    SDValue NewLoad =
+        DAG.getLoadVP(WideVT, DL, LD->getChain(), LD->getBasePtr(), Mask, EVL,
+                      MMO->getPointerInfo(), MMO->getAlign(), MMO->getFlags(),
+                      MMO->getAAInfo());
+
+    // Modified the chain - switch anything that used the old chain to use
+    // the new one.
+    ReplaceValueWith(SDValue(N, 1), NewLoad.getValue(1));
+
+    return NewLoad;
   }
 
   report_fatal_error("Unable to widen vector load");
 }
 
 SDValue DAGTypeLegalizer::WidenVecRes_MLOAD(MaskedLoadSDNode *N) {
 
   EVT WidenVT = TLI.getTypeToTransformTo(*DAG.getContext(),N->getValueType(0));

llvm/test/CodeGen/RISCV/rvv/legalize-load-sdnode.ll

 ; CHECK-NEXT:    slli a2, a1, 2
 ; CHECK-NEXT:    add a1, a2, a1
 ; CHECK-NEXT:    vsetvli zero, a1, e16, m2, ta, mu
 ; CHECK-NEXT:    vle16.v v8, (a0)
 ; CHECK-NEXT:    ret
   %v = load <vscale x 5 x half>, <vscale x 5 x half>* %ptr
   ret <vscale x 5 x half> %v
 }
+
+define <vscale x 7 x half> @load_nxv7f16(<vscale x 7 x half>* %ptr, <vscale x 7 x half>* %out) {
+; CHECK-LABEL: load_nxv7f16:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    csrr a2, vlenb
+; CHECK-NEXT:    srli a2, a2, 3
+; CHECK-NEXT:    slli a3, a2, 3
+; CHECK-NEXT:    sub a2, a3, a2
+; CHECK-NEXT:    vsetvli zero, a2, e16, m2, ta, mu
+; CHECK-NEXT:    vle16.v v8, (a0)
+; CHECK-NEXT:    vse16.v v8, (a1)
+; CHECK-NEXT:    ret
+  %v = load <vscale x 7 x half>, <vscale x 7 x half>* %ptr
+  store <vscale x 7 x half> %v, <vscale x 7 x half>* %out
+  ret <vscale x 7 x half> %v
+}