[cfe-dev] Sometimes throwing constructors / destructors

[Arnaud A. de Grandmaison]

I am a bit puzzled when looking at the IR generated for the following
testcase.

 

Why don’t we get an invoke for the first temporary constructor or destructor
call ?

At the same time, at other places in the exception path, the destructor for
the first temporary is assumed to be throwing as it is invoked (and not just
called).

 

$ cat testcase.cpp

struct X {

  X();

  ~X();

};

 

extern void use(const X &, const X &);

 

void test() {

  use(X(), X());

}

 

$ clang++ -O1 –S –emit-llvm –o – testcase.cpp

…

; Function Attrs: uwtable

define void @_Z4testv() #0 {

  %1 = alloca %struct.X, align 1

  %2 = alloca %struct.X, align 1

  call void @_ZN1XC1Ev(%struct.X* %1)                 ; ç non throwing
constructor ?

  invoke void @_ZN1XC1Ev(%struct.X* %2)

          to label %3 unwind label %6

 

; <label>:3                                       ; preds = %0

  invoke void @_Z3useRK1XS1_(%struct.X* dereferenceable(1) %1, %struct.X*
dereferenceable(1) %2)

          to label %4 unwind label %10

 

; <label>:4                                       ; preds = %3

  invoke void @_ZN1XD1Ev(%struct.X* %2)

          to label %5 unwind label %6

 

; <label>:5                                       ; preds = %4

  call void @_ZN1XD1Ev(%struct.X* %1)              ; ç non throwing
destructor ?

  ret void

 

; <label>:6                                       ; preds = %4, %0

  %7 = landingpad { i8*, i32 } personality i8* bitcast (i32 (...)*
@__gxx_personality_v0 to i8*)

          cleanup

  %8 = extractvalue { i8*, i32 } %7, 0

  %9 = extractvalue { i8*, i32 } %7, 1

  br label %14

 

; <label>:10                                      ; preds = %3

  %11 = landingpad { i8*, i32 } personality i8* bitcast (i32 (...)*
@__gxx_personality_v0 to i8*)

          cleanup

  %12 = extractvalue { i8*, i32 } %11, 0

  %13 = extractvalue { i8*, i32 } %11, 1

  invoke void @_ZN1XD1Ev(%struct.X* %2)

          to label %14 unwind label %18

 

; <label>:14                                      ; preds = %10, %6

  %.01 = phi i8* [ %8, %6 ], [ %12, %10 ]

  %.0 = phi i32 [ %9, %6 ], [ %13, %10 ]

  invoke void @_ZN1XD1Ev(%struct.X* %1)

          to label %15 unwind label %18                  ; ç throwing
destructor ?

 

; <label>:15                                      ; preds = %14

  %16 = insertvalue { i8*, i32 } undef, i8* %.01, 0

  %17 = insertvalue { i8*, i32 } %16, i32 %.0, 1

  resume { i8*, i32 } %17

 

; <label>:18                                      ; preds = %14, %10

  %19 = landingpad { i8*, i32 } personality i8* bitcast (i32 (...)*
@__gxx_personality_v0 to i8*)

          catch i8* null

  %20 = extractvalue { i8*, i32 } %19, 0

  call void @__clang_call_terminate(i8* %20) #3

  unreachable

}

 

--

Arnaud A. de Grandmaison

 
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