SelectionDAG: Add KnownBits and SignBits computation for EXTRACT_ELEMENT
v2: use getZExtValue
add missing break
codestyle
v3: add few more comments
Signed-off-by: Jan Vesely <jan.vesely@rutgers.edu>
Reviewed-by: Matt Arsenault <Matthew.Arsenault@amd.com>
llvm-svn: 226880
diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
index 13f62e7..24e9df3 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -2344,6 +2344,21 @@
KnownZero = APInt::getHighBitsSet(BitWidth, Leaders);
break;
}
+ case ISD::EXTRACT_ELEMENT: {
+ computeKnownBits(Op.getOperand(0), KnownZero, KnownOne, Depth+1);
+ const unsigned Index =
+ cast<ConstantSDNode>(Op.getOperand(1))->getZExtValue();
+ const unsigned BitWidth = Op.getValueType().getSizeInBits();
+
+ // Remove low part of known bits mask
+ KnownZero = KnownZero.getHiBits(KnownZero.getBitWidth() - Index * BitWidth);
+ KnownOne = KnownOne.getHiBits(KnownOne.getBitWidth() - Index * BitWidth);
+
+ // Remove high part of known bit mask
+ KnownZero = KnownZero.trunc(BitWidth);
+ KnownOne = KnownOne.trunc(BitWidth);
+ break;
+ }
case ISD::FrameIndex:
case ISD::TargetFrameIndex:
if (unsigned Align = InferPtrAlignment(Op)) {
@@ -2543,6 +2558,21 @@
// FIXME: it's tricky to do anything useful for this, but it is an important
// case for targets like X86.
break;
+ case ISD::EXTRACT_ELEMENT: {
+ const int KnownSign = ComputeNumSignBits(Op.getOperand(0), Depth+1);
+ const int BitWidth = Op.getValueType().getSizeInBits();
+ const int Items =
+ Op.getOperand(0).getValueType().getSizeInBits() / BitWidth;
+
+ // Get reverse index (starting from 1), Op1 value indexes elements from
+ // little end. Sign starts at big end.
+ const int rIndex = Items - 1 -
+ cast<ConstantSDNode>(Op.getOperand(1))->getZExtValue();
+
+ // If the sign portion ends in our element the substraction gives correct
+ // result. Otherwise it gives either negative or > bitwidth result
+ return std::max(std::min(KnownSign - rIndex * BitWidth, BitWidth), 0);
+ }
}
// If we are looking at the loaded value of the SDNode.