llvm dev - Mar 2015 - [LLVMdev] Instruction::mayThrow not handling invoke's?

While improving ADCE, i notice that for


declare i32 @strlen(i8*) readnone

define i32 @test() {
; invoke of pure function should not be deleted!
invoke i32 @strlen( i8* null ) readnone
to label %Cont unwind label %Other ; <i32>:1 [#uses=0]

Cont: ; preds = %0
ret i32 0

Other: ; preds = %0
         %exn = landingpad {i8*, i32} personality i32 (...)*
@__gxx_personality_v0
                  cleanup
ret i32 1
}

declare i32 @__gxx_personality_v0(...)

Instruction:: mayThrow returns false for the invoke.

This is because ...


 bool Instruction::mayThrow() const {
   if (const CallInst *CI = dyn_cast<CallInst>(this))
     return !CI->doesNotThrow();
   return isa<ResumeInst>(this);
 }

CallInst != InvokeInst, and invokeinst is not derived from callinst.

Am I missing something, or should this function also have:

 if (const InvokeInst *II = dyn_cast<InvokeInst>(this))
 return !II->doesNotThrow();

?
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After talking with Nick (the real reason i asked is because
mayHaveSideEffects returns false for this invoke), we don't consider the
control flow change of invoke to be a side effects.

On Wed, Mar 25, 2015 at 12:36 PM, Daniel Berlin <dberlin at dberlin.org>
wrote:
> While improving ADCE, i notice that for
>
>
> declare i32 @strlen(i8*) readnone
>
> define i32 @test() {
> ; invoke of pure function should not be deleted!
> invoke i32 @strlen( i8* null ) readnone
> to label %Cont unwind label %Other ; <i32>:1 [#uses=0]
>
> Cont: ; preds = %0
> ret i32 0
>
> Other: ; preds = %0
>          %exn = landingpad {i8*, i32} personality i32 (...)*
> @__gxx_personality_v0
>                   cleanup
> ret i32 1
> }
>
> declare i32 @__gxx_personality_v0(...)
>
> Instruction:: mayThrow returns false for the invoke.
>
> This is because ...
>
>
>  bool Instruction::mayThrow() const {
>    if (const CallInst *CI = dyn_cast<CallInst>(this))
>      return !CI->doesNotThrow();
>    return isa<ResumeInst>(this);
>  }
>
> CallInst != InvokeInst, and invokeinst is not derived from callinst.
>
> Am I missing something, or should this function also have:
>
>  if (const InvokeInst *II = dyn_cast<InvokeInst>(this))
>  return !II->doesNotThrow();
>
> ?
>
>
>
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Here is an interesting spin on this topic --
https://llvm.org/bugs/show_bug.cgi?id=24185

On Wed, Mar 25, 2015 at 1:43 PM, Daniel Berlin <dberlin at dberlin.org>
wrote:
> After talking with Nick (the real reason i asked is because
> mayHaveSideEffects returns false for this invoke), we don't consider
the
> control flow change of invoke to be a side effects.
>
> On Wed, Mar 25, 2015 at 12:36 PM, Daniel Berlin <dberlin at
dberlin.org> wrote:
>>
>> While improving ADCE, i notice that for
>>
>>
>> declare i32 @strlen(i8*) readnone
>>
>> define i32 @test() {
>> ; invoke of pure function should not be deleted!
>> invoke i32 @strlen( i8* null ) readnone
>> to label %Cont unwind label %Other ; <i32>:1 [#uses=0]
>>
>> Cont: ; preds = %0
>> ret i32 0
>>
>> Other: ; preds = %0
>>          %exn = landingpad {i8*, i32} personality i32 (...)*
>> @__gxx_personality_v0
>>                   cleanup
>> ret i32 1
>> }
>>
>> declare i32 @__gxx_personality_v0(...)
>>
>> Instruction:: mayThrow returns false for the invoke.
>>
>> This is because ...
>>
>>
>>  bool Instruction::mayThrow() const {
>>    if (const CallInst *CI = dyn_cast<CallInst>(this))
>>      return !CI->doesNotThrow();
>>    return isa<ResumeInst>(this);
>>  }
>>
>> CallInst != InvokeInst, and invokeinst is not derived from callinst.
>>
>> Am I missing something, or should this function also have:
>>
>>  if (const InvokeInst *II = dyn_cast<InvokeInst>(this))
>>  return !II->doesNotThrow();
>>
>> ?
>>
>>
>
>
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