[LLVMdev] Getelementptr woes

[Vladimir Prus]

Hello,
I'm having problems with the following LLVM instruction

  %tmp.0.i = call int (sbyte*, ...)*
        %printf( sbyte* getelementptr ([11 x sbyte]*  %.str_1, long 0, ......

The first argument in function call, 

    sbyte* getelementptr ([11 x sbyte]*  %.str_1.....

appears to be ConstantExpression*, and my backend does not support 
ConstantExpression yet.

I probable can implement that, and getelementptr instruction too, but I wonder 
if I need to. Looking at X86 backend, I see it does some smart things, like 
folding getelementptr into instruction which uses it, and using 'lea' asm 
instruction to perform addressing.

On my target, neither of this is possible -- there's just no such fancy 
addressing modes.

So I wonder if I can away by writing two passes which work on LLVM level.
The first pass would extract all ConstantExpr* operands from instructions and 
move them into separate instructions. E.g. the example above would become: 

  %tmp.1 = sbyte* getelementptr ([11 x sbyte]*  %.str_1, ..........
  %tmp.0.i = call int (sbyte*, ...)*
        %printf(%tmp.1 , .........

The second pass would convert getelementptr into casts and pointer arithmetic.

As a result, my backend would not care about both ConstantExpr and getelement 
ptr, both of which look scary. The biggest advantage is any target which does 
not have fancy addressing modes can just use those two passes.

I've started to sketch such passes already, but would be intetested to know 
what you think.

TIA,
Volodya