llvm dev - Apr 2018 - [InstCombine] Missed optimizations when null check before return statement

Hello,

Please check code:
https://godbolt.org/g/wtimXj

Clang surprisingly generates worse code for common pattern
if (!ptr)
    return NULL;

than for
if (!ptr)
    return ptr;


Gcc generates same code.

I checked the InstCombine's code and tried something to fix it but no
success.
So I will leave this here for more skilled developers and maybe the could
fix this problem.
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