Subzero. Adds a pass for target-specific helper call generation.

src/IceTargetLowering.h

Index: src/IceTargetLowering.h
diff --git a/src/IceTargetLowering.h b/src/IceTargetLowering.h
index c613d99d072b7d45b338c381cc34ea11a63681a8..5489b8b069486cd3c9b6c38b79de305f724ec89e 100644
--- a/src/IceTargetLowering.h
+++ b/src/IceTargetLowering.h
@@ -170,6 +170,8 @@ public:
     Func->setError("Target doesn't specify O2 lowering steps.");
   }
 
+  /// Generates calls to intrinsics for operations the Target can't handle.
+  void genTargetHelperCalls();
   /// Tries to do address mode optimization on a single instruction.
   void doAddressOpt();
   /// Randomly insert NOPs.
@@ -308,6 +310,8 @@ protected:
   virtual void lowerUnreachable(const InstUnreachable *Inst) = 0;
   virtual void lowerOther(const Inst *Instr);
 
+  virtual void genTargetHelperCallFor(Inst *Instr) = 0;
+
   virtual void doAddressOptLoad() {}
   virtual void doAddressOptStore() {}
   virtual void doMockBoundsCheck(Operand *) {}