[llvm-bugs] [Bug 36476] [InstCombine] Instcombine deletes call of 'new' function that has side effects after r325630

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=36476

Richard Smith <richard-llvm at metafoo.co.uk> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |INVALID
             Status|NEW                         |RESOLVED
                 CC|                            |richard-llvm at metafoo.co.uk

--- Comment #1 from Richard Smith <richard-llvm at metafoo.co.uk> ---
C++ [expr.new]p10 (http://eel.is/c++draft/expr.new#10) explicitly permits this
optimization:

"An implementation is allowed to omit a call to a replaceable global allocation
function ([new.delete.single], [new.delete.array]). When it does so, the
storage is instead provided by the implementation"

If you want to observe side-effects of your '::operator new(size_t)'
implementation (eg, when writing tests for your allocator), you need to make a
regular function call, rather than using a new-expression. LLVM will not delete
the 'operator new' call here:

    S *s = new (::operator new(sizeof(S))) S;

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