[LLVMdev] type promotion i16 -> i32

[Jim Grosbach]

On Jun 23, 2011, at 8:47 AM, Giovanni Ansaloni wrote:

> 
> Hello,
>  I'm developing a llvm backend. It seems that, if i16 is not a legal type
> (no register can hold i16 types in RegisterInfo.td and as a RegisterClass in
> SelLowering.cpp), i16 should be promoted to i32.

Arithmetic operations will be promoted to the next-smallest legal type (i32 usually). Loads and stores, however, will not. You still need to implement patterns for those. In particular, the extending loads and truncating stores.

-Jim

> Nonotheless, this simple program:
> 
> int main(){
>  volatile short a;
>  a= 3;
>  return 0;
> }
> 
> which is trasformed in this IR:
> 
> define i32 @main() nounwind readnone {
> entry:
>  %a = alloca i16, align 2                        ; <i16*> [#uses=1]
>  volatile store i16 3, i16* %a, align 2
>  ret i32 0
> }
> 
> fails to compile with the following error:
> 
> LLVM ERROR: Cannot yet select: 0x181c2d0: ch = store 0x1204a08, 0x181c248,
> 0x181be90, 0x181bfa0 <0x12022ec:0> <trunc i16> <volatile> alignment=2
> 
> Can anybody help?
> Thanks
> Giovanni.
> 
> -- 
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