Fix DivRem DAGCombine not to assume div/rem type is simple

[mkuper]

Summary

The divrem combine assumes the type of the div/rem is simple, which isn't necessarily true.
I'm guessing that it worked fine until r250825, since it probably only saw legal types, but now breaks when it runs as a pre-type-legalization combine.

This fixes PR26835.

lib/CodeGen/SelectionDAG/DAGCombiner.cpp

SDValue DAGCombiner::visitMUL(SDNode *N) {
 
   return SDValue();
 }
 
 /// Return true if divmod libcall is available.
 static bool isDivRemLibcallAvailable(SDNode *Node, bool isSigned,
                                      const TargetLowering &TLI) {
   RTLIB::Libcall LC;
-  switch (Node->getSimpleValueType(0).SimpleTy) {
+  EVT NodeType = Node->getValueType(0);
+  if (!NodeType.isSimple())
+    return false;
+  switch (NodeType.getSimpleVT().SimpleTy) {
   default: return false; // No libcall for vector types.
   case MVT::i8:   LC= isSigned ? RTLIB::SDIVREM_I8  : RTLIB::UDIVREM_I8;  break;
   case MVT::i16:  LC= isSigned ? RTLIB::SDIVREM_I16 : RTLIB::UDIVREM_I16; break;
   case MVT::i32:  LC= isSigned ? RTLIB::SDIVREM_I32 : RTLIB::UDIVREM_I32; break;
   case MVT::i64:  LC= isSigned ? RTLIB::SDIVREM_I64 : RTLIB::UDIVREM_I64; break;
   case MVT::i128: LC= isSigned ? RTLIB::SDIVREM_I128:RTLIB::UDIVREM_I128; break;
   }
 

test/CodeGen/X86/pr26835.ll

+; RUN: llc < %s | FileCheck %s
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-pc-linux"
+
+; CHECK-LABEL: foo
+; CHECK: div
+define i24 @foo(i24 %a, i24 %b) {
+  %r = urem i24 %a, %b
+  ret i24 %r
+}