[LLVMdev] How distinguish Catch all llvm-IR from other catch type ?

[Török Edwin]

On 2009-05-12 10:03, zhengjian zhang wrote:
> Hi,
>
> catch_all.cpp:
>
>      1  int main()
>      2  {
>      3      try {
>      4          throw 34;
>      5      }
>      6      catch (...) {}
>      7  }
>
>
> llvm-gcc -O3 -S -emit-llvm  catch_all.cpp   -o catch_all.ll:
>
>      1  ; ModuleID = 'catch_all.cpp'
>      2  target datalayout =
> "e-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-f32:32:32-f64:32:64-v64:64:64-v128:128:128-a0:0:64-f80:32:32"
>      3  target triple = "i386-pc-linux-gnu"
>      4          %struct.__fundamental_type_info_pseudo = type {
> %struct.__type_info_pseudo }
>      5          %struct.__type_info_pseudo = type { i8*, i8* }
>      6  @_ZTIi = external constant
> %struct.__fundamental_type_info_pseudo               ;
> <%struct.__fundamental_type_info_pseudo*> [#uses=1]
>      7
>      8  define i32 @main() {
>      9  entry:
>     10          %0 = tail call i8* @__cxa_allocate_exception(i32 4)
> nounwind            ; <i8*> [#uses=2]
>     11          %1 = bitcast i8* %0 to i32*             ; <i32*> [#uses=1]
>     12          store i32 34, i32* %1, align 4
>     13          invoke void @__cxa_throw(i8* %0, i8* bitcast
> (%struct.__fundamental_type_info_pseudo* @_ZTIi to i8*), void (i8*)*
> null) noreturn
>     14                          to label %invcont unwind label %lpad
>     15
>     16  invcont:                ; preds = %entry
>     17          unreachable
>     18
>     19  lpad:           ; preds = %entry
>     20          %eh_ptr = tail call i8* @llvm.eh.exception()
>  ; <i8*> [#uses=2]
>     21          %eh_select = tail call i32 (i8*, i8*, ...)*
> @llvm.eh.selector.i32(i8* %eh_ptr, i8* bitcast (i32 (...)*
> @__gxx_personality_sj0 to i8*))          ; <i32> [#uses=0]
>     22          %2 = tail call i8* @__cxa_begin_catch(i8* %eh_ptr)
> nounwind             ; <i8*> [#uses=0]
>     23          tail call void @__cxa_end_catch()
>     24          ret i32 0
>     25  }
>     26
>     27  declare i8* @__cxa_allocate_exception(i32) nounwind
>     28
>     29  declare void @__cxa_throw(i8*, i8*, void (i8*)*) noreturn
>     30
>     31  declare i8* @__cxa_begin_catch(i8*) nounwind
>     32
>     33  declare i8* @llvm.eh.exception() nounwind
>     34
>     35  declare i32 @llvm.eh.selector.i32(i8*, i8*, ...) nounwind
>     36
>     37  declare void @__cxa_end_catch()
>     38
>     39  declare i32 @__gxx_personality_sj0(...)
>
>
> from the LLVM-IR, catch all  was  translated  to  LLVM-IR :
> %eh_select = tail call i32 (i8*, i8*, ...)* @llvm.eh.selector.i32(i8*
> %eh_ptr, i8* bitcast (i32 (...)* @__gxx_personality_sj0 to i8*))
> here llvm.eh.selector.i32 has only two args,  but from the doc, it
> says llvm.eh.selector takes a minimum of three arguments.
>   

I get an extra null arg, I don't know why you don't:
    %eh_select = tail call i32 (i8*, i8*, ...)*
@llvm.eh.selector.i32(i8* %eh_ptr, i8* bitcast (i32 (...)*
@__gxx_personality_v0 to i8*), i8* null)        ; <i32> [#uses=0]

Compare it  with the IR generated for catch(int) or catch(someOtherType).

Here is how catch(int) looks like for me, notice the additional @_ZTIi
parameter, and the icmp for the typeid:

bb:        ; preds = %lpad
    %2 = tail call i8* @__cxa_begin_catch(i8* %eh_ptr) nounwind        ;
<i8*> [#uses=0]
    tail call void @__cxa_end_catch()
    ret i32 0

lpad: %eh_ptr = tail call i8* @llvm.eh.exception()        ; <i8*> [#uses=3]
    %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]
    %eh_typeid = tail call i32 @llvm.eh.typeid.for.i32(i8* bitcast
(%struct.__fundamental_type_info_pseudo* @_ZTIi to i8*))        ; <i32>
[#uses=1]
    %3 = icmp eq i32 %eh_select, %eh_typeid        ; <i1> [#uses=1]
    br i1 %3, label %bb, label %Unwind

Unwind:        ; preds = %lpad
    tail call void @_Unwind_Resume(i8* %eh_ptr)
    unreachable


Best regards,
--Edwin