[llvm-bugs] [Bug 44680] Optimizer breaks compare for the negation of the signed integer -0x80000000

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=44680

Dimitry Andric <dimitry at andric.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |INVALID
                 CC|                            |dimitry at andric.com
             Status|NEW                         |RESOLVED

--- Comment #1 from Dimitry Andric <dimitry at andric.com> ---
By negating what comes down to INT_MIN, you are invoking undefined behavior. 
If you compile your program with -fsanitize-undefined, and run it, you will see
the following:

$ ./pr44680-ubsan
pr44680.cpp:5:20: runtime error: negation of -2147483648 cannot be represented
in type 'int'; cast to an unsigned type to negate this value to itself
-2147483648 Is NaN :  true
-2147483648 < 0 : true
pr44680.cpp:13:30: runtime error: negation of -2147483648 cannot be represented
in type 'int'; cast to an unsigned type to negate this value to itself
pr44680.cpp:13:37: runtime error: negation of -2147483648 cannot be represented
in type 'int'; cast to an unsigned type to negate this value to itself
-2147483648 < 0 : true

See e.g. https://blog.regehr.org/archives/226 and
https://stackoverflow.com/a/37307948/6699433

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