[LLVMdev] tblgen and sign-extended constants too large for type

[Evan Cheng]

My feeling is tblgen shouldn't make assumptions about whether the  
backend will treat the value as signed or unsigned (after all  
MVT::ValueType does not convey sign information). Perhaps it's cleaner  
to just check if it fits as unsigned? Chris?

Evan

On Feb 8, 2008, at 6:43 PM, Scott Michel wrote:

> Question: How hard should tblgen try to fit constants into a  
> particular
> type?
>
> My case is an xor with i8 immediate where I'm using 0xff in as the
> immediate value. 0xff should fit into i8 if treated as unsigned, but
> CodeGenDAGPatterns.cpp assumes that any and all integers less than
> 32-bits are signed.
>
> Should tblgen try to see if the sign-extended version of the constant
> could fit into the type, and failing that, try the unsigned version:
>
> Index: utils/TableGen/CodeGenDAGPatterns.cpp
> ===================================================================
> --- utils/TableGen/CodeGenDAGPatterns.cpp	(revision 8028)
> +++ utils/TableGen/CodeGenDAGPatterns.cpp	(working copy)
> @@ -685,10 +685,17 @@
>           // Make sure that the value is representable for this type.
>           if (Size < 32) {
>             int Val = (II->getValue() << (32-Size)) >> (32-Size);
> -            if (Val != II->getValue())
> -              TP.error("Sign-extended integer value '" +
> itostr(II->getValue())+
> -                       "' is out of range for type '" +
> -                       getEnumName(getTypeNum(0)) + "'!");
> +            if (Val != II->getValue()) {
> +	      // If sign-extended doesn't fit, does it fit as unsigned?
> +	      unsigned ValueMask = unsigned(MVT::getIntVTBitMask(VT));
> +	      unsigned UnsignedVal = unsigned(II->getValue());
> +
> +	      if ((ValueMask & UnsignedVal) != UnsignedVal) {
> +		TP.error("Integer value '" + itostr(II->getValue())+
> +			 "' is out of range for type '" +
> +			 getEnumName(getTypeNum(0)) + "'!");
> +	      }
> +	    }
>
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev