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Add some notes for expanding clz/ctz 

llvm-svn: 21862
This commit is contained in:
Chris Lattner 2005-05-11 05:27:09 +00:00
parent 05309bf58e
commit 7247324047
1 changed files with 21 additions and 4 deletions
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25
llvm/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp
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@ -1132,10 +1132,27 @@ SDOperand SelectionDAGLegalize::LegalizeOp(SDOperand Op) {
Result = Tmp1;
break;
}
// case ISD::CTTZ:
// break;
// case ISD::CTLZ:
// break;
case ISD::CTTZ:
/* This should be used for targets that support ctpop:
int nlz5(unsigned x) {
int pop(unsigned x);
x = x | (x >> 1);
x = x | (x >> 2);
x = x | (x >> 4);
x = x | (x >> 8);
x = x | (x >>16);
return ctpop(~x);
}
See also: http://www.hackersdelight.org/HDcode/nlz.cc
*/
assert(0 && "Cannot expand this yet!");
break;
case ISD::CTLZ:
// See Also: http://www.hackersdelight.org/HDcode/ntz.cc
assert(0 && "Cannot expand this yet!");
break;
default:
assert(0 && "Cannot expand this yet!");
break;