[LLVMdev] missed optimizations

[Cédric Venet]

Nuno Lopes a écrit :
> Hi,
> 
> I have two questions about optimizations performed by llvm.
> 
> Consider these simple functions:
> int x(int b) { return b?4:6; }
> int y() { return x(0); }
> 
> int x2() { return 5; }
> int y2() { return x2(); }
> 
> the optimized bitcode (with clang + opt -std-compiler-opts) is:
> define i32 @y(...) nounwind {
> entry:
>  ret i32 6
> }
> 
> define i32 @y2(...) nounwind {
> entry:
>  %call = call i32 (...)* @x2( )  ; <i32> [#uses=0]
>  ret i32 5
> }
> 
> So why does LLVM optimizes the more difficult case, but leaves behind the 
> function call in the easiest case? :)
> 

I don't know why vararg would inhibit optimisation but maybe it is the 
problem.
You should try with:

int x2(void) { return 5; }
int y2(void) { return x2(); }

it may solve the problem (or use C++ as langage)

Cédric