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Add some notes for expanding clz/ctz

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@21862 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner
2005-05-11 05:27:09 +00:00
parent e3ef0a8b9f
commit 18aa680a96
1 changed files with 21 additions and 4 deletions
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25
lib/CodeGen/SelectionDAG/LegalizeDAG.cpp
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@@ -1132,10 +1132,27 @@ SDOperand SelectionDAGLegalize::LegalizeOp(SDOperand Op) {
Result = Tmp1; Result = Tmp1;
break; break;
} }
// case ISD::CTTZ: case ISD::CTTZ:
// break; /* This should be used for targets that support ctpop:
// case ISD::CTLZ: int nlz5(unsigned x) {
// break; 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: default:
assert(0 && "Cannot expand this yet!"); assert(0 && "Cannot expand this yet!");
break; break;