[LLVMdev] Code generation problem

Nick Lewycky nicholas at mxc.ca
Mon Feb 15 14:15:56 PST 2010

Russell Wallace wrote:
> Oh! Okay, thanks, I'll fix it up to do that then.
> Any chance verifyFunction could be tightened up to catch this case?
> I'm currently running all my generated code through it, and it passes
> the i32 conditional without complaint.

Done in r96282. Thanks for the bug report!


> On Mon, Feb 8, 2010 at 10:07 PM, John McCall<rjmccall at apple.com>  wrote:
>> On Feb 8, 2010, at 1:53 PM, Russell Wallace wrote:
>>> I was testing my implementation of the usual ternary function just
>>> now, and it's giving the wrong answer; I would attribute this to an
>>> error in my parser/abstract syntax tree code, but looking at the
>>> output, as far as I can see, the intermediate code is correct at the
>>> point where I hand it to LLVM's JIT. Could someone look and see if I'm
>>> doing something wrong, misunderstanding the semantics of the
>>> intermediate code format or something?
>> The condition on a branch instruction is not evaluated with C condition
>> semantics.  It must be of i1 type, i.e. either true or false.  Your IR should
>> (presumably) be more like:
>>   %c1 = icmp ne i32 1, i32 0
>>    br i1 %c1, label %yes, label %no
>> yes:
>>   %c2 = icmp ne i32 2, i32 0
>>   br i1 %c2, ....
>> Also, if you are producing IR yourself, you should always be running the IR
>> verification pass (at least in debug mode), which should catch structural
>> problems like this (and many others).
>> John.
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