[jepler]

https://godbolt.org/z/z-92qR

Interestingly, the compiler emits no call to malloc, even. What!?

[steerablesafe]

With -fno-builtin. It's still "cheating" as b is local.

https://godbolt.org/z/U5VGxt

Without cheating:

https://godbolt.org/z/rzcXg2

It doesn't optimize the two stores to b away.

[gpderetta]

The compiler knows the semantics of malloc. Malloc as it appear in the source code doesn't even need to map 1:1 to calls to the library function, the compiler can remove and coalesce calls at will.