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

[Scott Michel]

Allow me to rephrase my question: How much agony and gnashing of  
teeth will I cause if I commit this patch to tblgen (fully tested and  
changes to DAGISelEmitter.cpp also committed)?


-scooter

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)) + "'!");
> +	      }
> +	    }
>
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