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SelectionDAG: create correct BooleanContent constants

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Occasionally DAGCombiner can spot that a SETCC operation is completely
redundant and reduce it to "all true" or "all false". If this happens to a
vector, the value produced has to take account of what a normal comparison
would have produced, which may be an all-1s bitmask.

The fix in SelectionDAG.cpp is tested, however, as far as I can see the code in
TargetLowering.cpp is possibly unreachable and almost certainly irrelevant when
triggered so there are no tests. However, I believe it's still clearly the
right change and may save someone else some hassle if it suddenly becomes
reachable. So I'm doing it anyway.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@190147 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Tim Northover
2013-09-06 12:38:12 +00:00
parent 888497d8a2
commit a5eeb9da05
3 changed files with 72 additions and 2 deletions
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lib/CodeGen/SelectionDAG/TargetLowering.cpp
+5 -1
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@@ -1080,7 +1080,11 @@ TargetLowering::SimplifySetCC(EVT VT, SDValue N0, SDValue N1,
case ISD::SETFALSE:
case ISD::SETFALSE2: return DAG.getConstant(0, VT);
case ISD::SETTRUE:
case ISD::SETTRUE2: return DAG.getConstant(1, VT);
case ISD::SETTRUE2: {
TargetLowering::BooleanContent Cnt = getBooleanContents(VT.isVector());
return DAG.getConstant(
Cnt == TargetLowering::ZeroOrNegativeOneBooleanContent ? -1ULL : 1, VT);
}
}
// Ensure that the constant occurs on the RHS, and fold constant