Add our own legacy loop unswitch pass (#1339)

Since legacy binding for loop unswitch pass was removed and we can't get
it back. Implement its equivalent in `aot_llvm_extra.cpp` and use it in
`aot_compiler.c`.

Follow up to #1183.

core/iwasm/compilation/aot_compiler.c

@@ -2643,9 +2643,8 @@ apply_func_passes(AOTCompContext *comp_ctx)
         LLVMAddLoopRotatePass(pass_mgr);
 #if LLVM_VERSION_MAJOR < 15
         LLVMAddLoopUnswitchPass(pass_mgr);
-        /* Binding disabled in LLVM 15, don't add the pass util we can either
-           add a binding to SimpleLoopUnswitchPass, or add it to
-           aot_llvm_extra.cpp */
+#else
+        aot_add_simple_loop_unswitch_pass(pass_mgr);
 #endif
         LLVMAddInstructionCombiningPass(pass_mgr);
         LLVMAddCFGSimplificationPass(pass_mgr);

core/iwasm/compilation/aot_llvm.h

@@ -499,6 +499,9 @@ aot_check_simd_compatibility(const char *arch_c_str, const char *cpu_c_str);
 void
 aot_add_expand_memory_op_pass(LLVMPassManagerRef pass);
 
+void
+aot_add_simple_loop_unswitch_pass(LLVMPassManagerRef pass);
+
 void
 aot_apply_llvm_new_pass_manager(AOTCompContext *comp_ctx);
 

core/iwasm/compilation/aot_llvm_extra.cpp

@@ -66,6 +66,9 @@ aot_check_simd_compatibility(const char *arch_c_str, const char *cpu_c_str);
 void
 aot_add_expand_memory_op_pass(LLVMPassManagerRef pass);
 
+void
+aot_add_simple_loop_unswitch_pass(LLVMPassManagerRef pass);
+
 void
 aot_func_disable_tce(LLVMValueRef func);
 
@@ -258,6 +261,12 @@ aot_add_expand_memory_op_pass(LLVMPassManagerRef pass)
     unwrap(pass)->add(new ExpandMemoryOpPass());
 }
 
+void
+aot_add_simple_loop_unswitch_pass(LLVMPassManagerRef pass)
+{
+    unwrap(pass)->add(createSimpleLoopUnswitchLegacyPass());
+}
+
 bool
 aot_check_simd_compatibility(const char *arch_c_str, const char *cpu_c_str)
 {