[llvm-dev] Wrong code bug after GVN/PRE?

Mikael Holmén via llvm-dev llvm-dev at lists.llvm.org
Sun Jan 22 23:54:18 PST 2017

Hi Philip,

On 01/21/2017 01:03 AM, Friedman, Eli wrote:
> On 1/20/2017 3:19 PM, Philip Reames via llvm-dev wrote:
>> If someone can produce an *IR* reproducer which they believe is
>> incorrect, I'm happy to take a look at the PRE code.  I will not have
>> the time to reproduce this from C or work through the interaction of
>> other passes;  I will only look at this if there is a bug with PRE
>> specific IR reproducer attached.
> https://llvm.org/bugs/show_bug.cgi?id=31651 has an IR testcase.

As Eli said, in the PR there is IR that I think is miscompiled if you 
run gvn on it.

In the PR and earlier in this thread I pasted some C-like code just to 
describe what I think is happening since I thought it was easier than 
pasting llvm assembler, but the pre_gvn.ll file in PR31651 can indeed be 
used to reproduce the problem by just running gvn on it.

Great if you could have a look!

> -Eli

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