[SystemZ] Add NoMerge MIFlag

[iii]

Summary

This fixes ASan and MSan tests on SystemZ after
commit 6a822e20ce70 ("[ASan][MSan] Remove EmptyAsm and set the CallInst
to nomerge to avoid from merging.").

Based on commit 80e107ccd088 ("Add NoMerge MIFlag to avoid MIR branch
folding").

[uweigand]

LGTM, thanks!

llvm/lib/Target/SystemZ/SystemZISelLowering.cpp

SystemZTargetLowering::LowerCall(CallLoweringInfo &CLI,
   if (Glue.getNode())
     Ops.push_back(Glue);
 
   // Emit the call.
   SDVTList NodeTys = DAG.getVTList(MVT::Other, MVT::Glue);
   if (IsTailCall)
     return DAG.getNode(SystemZISD::SIBCALL, DL, NodeTys, Ops);
   Chain = DAG.getNode(SystemZISD::CALL, DL, NodeTys, Ops);
+  DAG.addNoMergeSiteInfo(Chain.getNode(), CLI.NoMerge);
   Glue = Chain.getValue(1);
 
   // Mark the end of the call, which is glued to the call itself.
   Chain = DAG.getCALLSEQ_END(Chain,
                              DAG.getConstant(NumBytes, DL, PtrVT, true),
                              DAG.getConstant(0, DL, PtrVT, true),
                              Glue, DL);
   Glue = Chain.getValue(1);

llvm/test/CodeGen/SystemZ/nomerge.ll

+; RUN: llc < %s -mtriple=s390x-linux-gnu -o - | FileCheck %s
+
+define void @foo(i32 %i) {
+entry:
+  switch i32 %i, label %if.end3 [
+    i32 5, label %if.then
+    i32 7, label %if.then2
+  ]
+
+if.then:
+  tail call void @bar() #0
+  br label %if.end3
+
+if.then2:
+  tail call void @bar() #0
+  br label %if.end3
+
+if.end3:
+  tail call void @bar() #0
+  ret void
+}
+
+declare void @bar()
+
+attributes #0 = { nomerge }
+
+; CHECK-LABEL: foo:
+; CHECK: # %bb.0: # %entry
+; CHECK: # %bb.1: # %entry
+; CHECK: # %bb.2: # %if.then
+; CHECK-NEXT: brasl %r14, bar@PLT
+; CHECK: jg bar@PLT
+; CHECK: .LBB0_3: # %if.then2
+; CHECK: brasl %r14, bar@PLT
+; CHECK: .LBB0_4: # %if.end3
+; CHECK: jg bar@PLT