Avoid emitting OP_NOT_NULL opcodes in non-llvm mode, they are not used, and they keep their inputs alive.

Author: vargaz

src/mono/mono/mini/ir-emit.h

@@ -886,7 +886,7 @@ static int ccount = 0;
 		cfg->flags |= MONO_CFG_HAS_CHECK_THIS; \
 		MONO_EMIT_NEW_BIALU_IMM (cfg, OP_COMPARE_IMM, -1, (reg), 0);	\
 		MONO_EMIT_NEW_COND_EXC (cfg, EQ, "NullReferenceException");		\
-		MONO_EMIT_NEW_UNALU (cfg, OP_NOT_NULL, -1, reg); \
+		if (COMPILE_LLVM (cfg)) MONO_EMIT_NEW_UNALU (cfg, OP_NOT_NULL, -1, reg); \
 	} while (0)
 
 /* Emit an explicit null check which doesn't depend on SIGSEGV signal handling */
@@ -897,7 +897,7 @@ static int ccount = 0;
 		} else { \
 			MONO_EMIT_NEW_IMPLICIT_EXCEPTION_LOAD_STORE (cfg); \
 		} \
-		MONO_EMIT_NEW_UNALU (cfg, OP_NOT_NULL, -1, reg); \
+		if (COMPILE_LLVM (cfg)) MONO_EMIT_NEW_UNALU (cfg, OP_NOT_NULL, -1, reg); \
 	} while (0)
 
 #define MONO_EMIT_NEW_CHECK_THIS(cfg, sreg) do { \
@@ -907,7 +907,7 @@ static int ccount = 0;
 		} else { \
 			MONO_EMIT_NEW_UNALU (cfg, OP_CHECK_THIS, -1, sreg); \
 			MONO_EMIT_NEW_IMPLICIT_EXCEPTION_LOAD_STORE (cfg); \
-			MONO_EMIT_NEW_UNALU (cfg, OP_NOT_NULL, -1, sreg); \
+			if (COMPILE_LLVM (cfg)) MONO_EMIT_NEW_UNALU (cfg, OP_NOT_NULL, -1, sreg); \
 		} \
 	} while (0)