[LoongArch] Transfer MI flags when expand PseudoCALL

When expanding a PseudoCALL, the corresponding flags (e.g. nomerge)
need to be passed to the new instruction.

This patch also adds test for the nomerge attribute.

The `nomerge` attribute was added during `LowerCall`, but was lost
during expand PseudoCALL. Now add it back.

Reviewed By: SixWeining

Differential Revision: https://reviews.llvm.org/D137888

Author: wangleiat

llvm/lib/Target/LoongArch/LoongArchExpandPseudoInsts.cpp

@@ -285,6 +285,9 @@ bool LoongArchPreRAExpandPseudo::expandFunctionCALL(
   // Transfer implicit operands.
   CALL.copyImplicitOps(MI);
 
+  // Transfer MI flags.
+  CALL.setMIFlags(MI.getFlags());
+
   MI.eraseFromParent();
   return true;
 }

llvm/test/CodeGen/LoongArch/nomerge.ll

@@ -0,0 +1,35 @@
+; RUN: llc --mtriple=loongarch64 < %s | 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: bl %plt(bar)
+; CHECK: .LBB0_3: # %if.then2
+; CHECK-NEXT: bl %plt(bar)
+; CHECK: .LBB0_4: # %if.end3
+; CHECK: bl %plt(bar)