[llvm-dev] Dataflow analysis regression in 3.7

Johan Engelen via llvm-dev
Wed, 05 Jul 2017 22:59:45 -0000

Hi all,
  I just found an optimization regression regarding simple
dataflow/constprop analysis:
https://godbolt.org/g/Uz8P7t

This code
```
int dataflow(int b) {
  int a;

  if (b==4)
    a = 3*b; // fully optimized when changed to a = 3;
  else
    a = 5;

  if (a == 4)
    return 0;
  else
    return 1;
}
```
is no longer optimized to just a "return 1". The regression happened
in
LLVM 3.6 --> 3.7.

Is this a known regression? I couldn't find it in the bug tracker (but
don't really know which keywords to look for...)

Kind regards,
  Johan
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