Revert "[AMDGPU] Always lower s/udiv64 by constant to MUL (llvm#100723)"

This reverts commit 92fbc96.

The patch also affected ARM and caused an assertion failure during
CurDAG->Legalize
(llvm#100723 (comment)).

Author: MaskRay

llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp

@@ -6405,12 +6405,7 @@ SDValue TargetLowering::BuildSDIV(SDNode *N, SelectionDAG &DAG,
     if (VT.isVector())
       WideVT = EVT::getVectorVT(*DAG.getContext(), WideVT,
                                 VT.getVectorElementCount());
-    // Some targets like AMDGPU try to go from SDIV to SDIVREM which is then
-    // custom lowered. This is very expensive so avoid it at all costs for
-    // constant divisors.
-    if ((isOperationExpand(ISD::SDIV, VT) &&
-         isOperationCustom(ISD::SDIVREM, VT.getScalarType())) ||
-        isOperationLegalOrCustom(ISD::MUL, WideVT)) {
+    if (isOperationLegalOrCustom(ISD::MUL, WideVT)) {
       X = DAG.getNode(ISD::SIGN_EXTEND, dl, WideVT, X);
       Y = DAG.getNode(ISD::SIGN_EXTEND, dl, WideVT, Y);
       Y = DAG.getNode(ISD::MUL, dl, WideVT, X, Y);
@@ -6593,12 +6588,7 @@ SDValue TargetLowering::BuildUDIV(SDNode *N, SelectionDAG &DAG,
     if (VT.isVector())
       WideVT = EVT::getVectorVT(*DAG.getContext(), WideVT,
                                 VT.getVectorElementCount());
-    // Some targets like AMDGPU try to go from UDIV to UDIVREM which is then
-    // custom lowered. This is very expensive so avoid it at all costs for
-    // constant divisors.
-    if ((isOperationExpand(ISD::UDIV, VT) &&
-         isOperationCustom(ISD::UDIVREM, VT.getScalarType())) ||
-        isOperationLegalOrCustom(ISD::MUL, WideVT)) {
+    if (isOperationLegalOrCustom(ISD::MUL, WideVT)) {
       X = DAG.getNode(ISD::ZERO_EXTEND, dl, WideVT, X);
       Y = DAG.getNode(ISD::ZERO_EXTEND, dl, WideVT, Y);
       Y = DAG.getNode(ISD::MUL, dl, WideVT, X, Y);