llvm dev - Sep 2002 - [LLVMdev] Bug in InstructionCombining.cpp

ISSUE: This code:

%bob = type { int }

int %alias() {
    %pbob1 = alloca %bob
    %pbob2 = getelementptr %bob* %pbob1                   ;pbob2 aliases 
pbob1
    %pbobel = getelementptr %bob* %pbob2, long 0, ubyte 0
    %rval = load int* %pbobel
    ret int %rval
}

Crashes when run through opt -instcombine.  InstCombiner visits 
instructions in reverse declaration order, but 
InstCombiner::visitGetElementPtr() , when trying to combine %pbobel with 
%pbob2, assumes that aliases like %pbob2 have already been eliminated. 
 The result is a dereference of an invalid iterator, and an attempt to 
replace %pbobel with "getelementptr %bob* %pbob1, ubyte 0".

ACTION: When  combining constant index expressions in InstCombiner, 
treat the source index as 0 if not present.

-- 
Casey Carter
Casey at Carter.net
ccarter at uiuc.edu
AIM: cartec69

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> ISSUE: This code:
> Crashes when run through opt -instcombine.  InstCombiner visits
Fixed:
http://mail.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20020916/000286.html
http://mail.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20020916/000287.html

Thanks for finding this!  Dead bugs are the best kind.  :)

-Chris


> instructions in reverse declaration order, but
> InstCombiner::visitGetElementPtr() , when trying to combine %pbobel with
> %pbob2, assumes that aliases like %pbob2 have already been eliminated.
>  The result is a dereference of an invalid iterator, and an attempt to
> replace %pbobel with "getelementptr %bob* %pbob1, ubyte 0".
>
> ACTION: When  combining constant index expressions in InstCombiner,
> treat the source index as 0 if not present.
>
> --
> Casey Carter
> Casey at Carter.net
> ccarter at uiuc.edu
> AIM: cartec69
>
>
-Chris

http://llvm.cs.uiuc.edu/
http://www.nondot.org/~sabre/Projects/