Generalize the new code in instcombine's ComputeNumSignBits for handling
and/or to handle more cases (such as this add-sitofp.ll testcase), and
port it to selectiondag's ComputeNumSignBits.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@51469 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
index c46271a..ff505f2 100644
--- a/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ b/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -1628,6 +1628,7 @@
assert(MVT::isInteger(VT) && "Invalid VT!");
unsigned VTBits = MVT::getSizeInBits(VT);
unsigned Tmp, Tmp2;
+ unsigned FirstAnswer = 1;
if (Depth == 6)
return 1; // Limit search depth.
@@ -1683,11 +1684,16 @@
case ISD::AND:
case ISD::OR:
case ISD::XOR: // NOT is handled here.
- // Logical binary ops preserve the number of sign bits.
+ // Logical binary ops preserve the number of sign bits at the worst.
Tmp = ComputeNumSignBits(Op.getOperand(0), Depth+1);
- if (Tmp == 1) return 1; // Early out.
- Tmp2 = ComputeNumSignBits(Op.getOperand(1), Depth+1);
- return std::min(Tmp, Tmp2);
+ if (Tmp != 1) {
+ Tmp2 = ComputeNumSignBits(Op.getOperand(1), Depth+1);
+ FirstAnswer = std::min(Tmp, Tmp2);
+ // We computed what we know about the sign bits as our first
+ // answer. Now proceed to the generic code that uses
+ // ComputeMaskedBits, and pick whichever answer is better.
+ }
+ break;
case ISD::SELECT:
Tmp = ComputeNumSignBits(Op.getOperand(1), Depth+1);
@@ -1801,7 +1807,7 @@
Op.getOpcode() == ISD::INTRINSIC_W_CHAIN ||
Op.getOpcode() == ISD::INTRINSIC_VOID) {
unsigned NumBits = TLI.ComputeNumSignBitsForTargetNode(Op, Depth);
- if (NumBits > 1) return NumBits;
+ if (NumBits > 1) FirstAnswer = std::max(FirstAnswer, NumBits);
}
// Finally, if we can prove that the top bits of the result are 0's or 1's,
@@ -1816,7 +1822,7 @@
Mask = KnownOne;
} else {
// Nothing known.
- return 1;
+ return FirstAnswer;
}
// Okay, we know that the sign bit in Mask is set. Use CLZ to determine
@@ -1825,7 +1831,7 @@
Mask <<= Mask.getBitWidth()-VTBits;
// Return # leading zeros. We use 'min' here in case Val was zero before
// shifting. We don't want to return '64' as for an i32 "0".
- return std::min(VTBits, Mask.countLeadingZeros());
+ return std::max(FirstAnswer, std::min(VTBits, Mask.countLeadingZeros()));
}