[LLVMdev] How to disable simplifying function parameters in llvm-g++

[Duncan Sands]

Hi Xiaolong,

> I checked the result spit out by Clang (I have not found good reasons
> to switch to Clang until today :). It turned out that Clang preserves
> more accurate type information than llvm-g++, at least in my test
> cases.Back to the example in our discussion, the compiled function
> prototype is:
>
>    define linkonce_odr void @_ZNSt4listIiSaIiEE9_M_insertESt14_List_iteratorIiERKi(%"class.std::list"* %this, %"struct.std::_List_node_base"* %__position.coerce, i32* %__x) ssp align 2 { ... }
>
> Compared with llvm-g++, the second parameter is of type
> %"struct.std::_List_node_base"*, rather than a plain i64. Note that
> the fact does not impair your argument on the conformance to
> ABI. llvm-g++ may do better, however. :)

since the final assembler is the same, both of these approaches are
correct.  However the code produced by clang is likely to be more
easily optimizable.

Ciao,

Duncan.