Add NOP to ARM IR lowering.

src/IceInstARM32.cpp

Index: src/IceInstARM32.cpp
diff --git a/src/IceInstARM32.cpp b/src/IceInstARM32.cpp
index 920a93368e2b603642bff1492cac80f69e916012..b1d052cfa3c2e62cfc63b71bd5f1a92d6615caac 100644
--- a/src/IceInstARM32.cpp
+++ b/src/IceInstARM32.cpp
@@ -1221,6 +1221,12 @@ template <> void InstARM32Tst::emitIAS(const Cfg *Func) const {
     emitUsingTextFixup(Func);
 }
 
+InstARM32Dmb::InstARM32Dmb(Cfg *Func)
+    : InstARM32Pred(Func, InstARM32::Dmb, 0, nullptr, CondARM32::AL) {}
+
+InstARM32Nop::InstARM32Nop(Cfg *Func)
+    : InstARM32Pred(Func, InstARM32::Nop, 0, nullptr, CondARM32::AL) {}
+
 InstARM32Vcmp::InstARM32Vcmp(Cfg *Func, Variable *Src0, Operand *Src1,
                              CondARM32::Cond Predicate)
     : InstARM32Pred(Func, InstARM32::Vcmp, 2, nullptr, Predicate) {
@@ -1240,9 +1246,6 @@ InstARM32Vabs::InstARM32Vabs(Cfg *Func, Variable *Dest, Variable *Src,
   addSource(Src);
 }
 
-InstARM32Dmb::InstARM32Dmb(Cfg *Func)
-    : InstARM32Pred(Func, InstARM32::Dmb, 0, nullptr, CondARM32::AL) {}
-
 // ======================== Dump routines ======================== //
 
 // Two-addr ops
@@ -2447,6 +2450,26 @@ void InstARM32Dmb::dump(const Cfg *Func) const {
                                       "sy";
 }
 
+void InstARM32Nop::emit(const Cfg *Func) const {
+  if (!BuildDefs::dump())
+    return;
+  assert(getSrcSize() == 0);
+  Func->getContext()->getStrEmit() << "\t"
+                                   << "nop";
+}
+
+void InstARM32Nop::emitIAS(const Cfg *Func) const {
+  assert(getSrcSize() == 0);
+  Func->getAssembler<ARM32::AssemblerARM32>()->nop();
+}
+
+void InstARM32Nop::dump(const Cfg *Func) const {
+  if (!BuildDefs::dump())
+    return;
+  assert(getSrcSize() == 0);
+  Func->getContext()->getStrDump() << "nop";
+}
+
 void OperandARM32Mem::emit(const Cfg *Func) const {
   if (!BuildDefs::dump())
     return;