[LLVMdev] how to resolve llvm exception IR?

[zhengjian zhang]

here are the cpp file:
$ cat -n  eh1.catch.cpp
     1  #include <iostream>
     2
     3  int main()
     4  {
     5      try {
     6          throw 78;
     7      }
     8      catch (int){
     9
    10          std::cout << "at catch\n";
    11
    12      }
    13  }


LLVM-IR:

$ llvm-g++  -S -emit-llvm eh1.catch.cpp -o eh1.catch.ll

...
    46  define i32 @main() {
    47  entry:
    48          %0 = tail call i8* @__cxa_allocate_exception(i32 4)
nounwind            ; <i8*> [#uses=2]
    49          %1 = bitcast i8* %0 to i32*             ; <i32*> [#uses=1]
    50          store i32 78, i32* %1, align 4
    51          invoke void @__cxa_throw(i8* %0, i8* bitcast
(%struct.__fundamental_type_info_pseudo* @_ZTIi to i8*), void (i8*)*
null) noreturn
    52                          to label %invcont unwind label %lpad
    53
    54  invcont:                ; preds = %entry
    55          unreachable
    56
    57  bb:             ; preds = %lpad
    58          %2 = tail call i8* @__cxa_begin_catch(i8* %eh_ptr)
nounwind             ; <i8*> [#uses=0]
    59          %3 = invoke
%"struct.std::basic_ostream<char,std::char_traits<char> >"*
@_ZStlsISt11char_traitsIcEERSt13basic_ostreamIcT_ES5_PKc(%"struct.std::basic_ostream<char,std::char_traits<char>
>"* @_ZSt4cout, i8* getelementptr ([10 x i8]* @.str, i32 0, i32 0))
    60                          to label %bb6 unwind label %lpad10
         ; <%"struct.std::basic_ostream<char,std::char_traits<char>
>"*> [#uses=0]
    61
    62  bb6:            ; preds = %bb
    63          tail call void @__cxa_end_catch()
    64          ret i32 0
    65
    66  lpad:           ; preds = %entry
    67          %eh_ptr = tail call i8* @llvm.eh.exception()
 ; <i8*> [#uses=3]
    68          %eh_select9 = tail call i32 (i8*, i8*, ...)*
@llvm.eh.selector.i32(i8* %eh_ptr, i8* bitcast (i32 (...)*
@__gxx_personality_v0 to i8*), i8* bitcast
(%struct.__fundamental_type_info_pseudo* @_ZTIi to i8*), i8* null)
     ; <i32> [#uses=1]
    69          %eh_typeid = tail call i32 @llvm.eh.typeid.for.i32(i8*
bitcast (%struct.__fundamental_type_info_pseudo* @_ZTIi to i8*))
  ; <i32> [#uses=1]
    70          %4 = icmp eq i32 %eh_select9, %eh_typeid
 ; <i1> [#uses=1]
    71          br i1 %4, label %bb, label %Unwind
    72
    73  lpad10:         ; preds = %bb
    74          %eh_ptr11 = tail call i8* @llvm.eh.exception()
 ; <i8*> [#uses=2]
    75          %eh_select13 = tail call i32 (i8*, i8*, ...)*
@llvm.eh.selector.i32(i8* %eh_ptr11, i8* bitcast (i32 (...)*
@__gxx_personality_v0 to i8*), i8* null)             ; <i32> [#uses=0]
    76          invoke void @__cxa_end_catch()
    77                          to label %Unwind unwind label %lpad14
    78
    79  lpad14:         ; preds = %lpad10
    80          %eh_ptr15 = tail call i8* @llvm.eh.exception()
 ; <i8*> [#uses=1]
    81          %eh_select17 = tail call i32 (i8*, i8*, ...)*
@llvm.eh.selector.i32(i8* %eh_ptr15, i8* bitcast (i32 (...)*
@__gxx_personality_v0 to i8*))               ; <i32> [#uses=0]
    82          tail call void @_ZSt9terminatev() noreturn nounwind
    83          unreachable
    84
    85  Unwind:         ; preds = %lpad10, %lpad
    86          %eh_exception.0 = phi i8* [ %eh_ptr, %lpad ], [
%eh_ptr11, %lpad10 ]            ; <i8*> [#uses=1]
    87          tail call void @_Unwind_Resume(i8* %eh_exception.0)
    88          unreachable
    89  }


my  question is at line 59  can throw an exception?

here is another cpp file:
$ cat -n  eh1.try.cpp
     1  #include <iostream>
     2
     3
     4
     5  int main()
     6  {
     7      try {
     8          std::cout << "before throw\n";
     9          throw 78;
    10
    11      }
    12      catch (int){
    13
    14      }
    15  }

the generated LLVM-IR :

46  define i32 @main() {
    47  entry:
    48          %0 = invoke
%"struct.std::basic_ostream<char,std::char_traits<char> >"*
@_ZStlsISt11char_traitsIcEERSt13basic_ostreamIcT_ES5_PKc(%"struct.std::basic_ostream<char,std::char_traits<char>
>"* @_ZSt4cout, i8* getelementptr ([14 x i8]* @.str, i32 0, i32 0))
    49                          to label %invcont unwind label %lpad
         ; <%"struct.std::basic_ostream<char,std::char_traits<char>
>"*> [#uses=0]
    50
    51  invcont:                ; preds = %entry
    52          %1 = tail call i8* @__cxa_allocate_exception(i32 4)
nounwind            ; <i8*> [#uses=2]
    53          %2 = bitcast i8* %1 to i32*             ; <i32*> [#uses=1]
    54          store i32 78, i32* %2, align 4
    55          invoke void @__cxa_throw(i8* %1, i8* bitcast
(%struct.__fundamental_type_info_pseudo* @_ZTIi to i8*), void (i8*)*
null) noreturn
    56                          to label %invcont1 unwind label %lpad
    57
    58  invcont1:               ; preds = %invcont
    59          unreachable
    60
    61  bb:             ; preds = %lpad
    62          %3 = tail call i8* @__cxa_begin_catch(i8* %eh_ptr)
nounwind             ; <i8*> [#uses=0]
    63          tail call void @__cxa_end_catch()
    64          ret i32 0
    65
    66  lpad:           ; preds = %invcont, %entry
    67          %eh_ptr = tail call i8* @llvm.eh.exception()
 ; <i8*> [#uses=3]
    68          %eh_select = tail call i32 (i8*, i8*, ...)*
@llvm.eh.selector.i32(i8* %eh_ptr, i8* bitcast (i32 (...)*
@__gxx_personality_v0 to i8*), i8* bitcast
(%struct.__fundamental_type_info_pseudo* @_ZTIi to i8*), i8* null)
      ; <i32> [#uses=1]
    69          %eh_typeid = tail call i32 @llvm.eh.typeid.for.i32(i8*
bitcast (%struct.__fundamental_type_info_pseudo* @_ZTIi to i8*))
  ; <i32> [#uses=1]
    70          %4 = icmp eq i32 %eh_select, %eh_typeid         ; <i1> [#uses=1]
    71          br i1 %4, label %bb, label %Unwind
    72
    73  Unwind:         ; preds = %lpad
    74          tail call void @_Unwind_Resume(i8* %eh_ptr)
    75          unreachable
    76  }

here at line 48 can throw an exception?

my another problem :  are there any different of above two  llmv-ir
on  handle c++ exception  ?


best regards
zhangzw
2009-4-28