1 files changed, 19 insertions, 0 deletions
diff --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
index dd694281521..217c0e6ce48 100644
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -33508,6 +33508,25 @@ bool X86TargetLowering::SimplifyDemandedBitsForTargetNode(
     }
     break;
   }
+  case X86ISD::PACKSS:
+    // PACKSS saturates to MIN/MAX integer values. So if we just want the
+    // sign bit then we can just ask for the source operands sign bit.
+    // TODO - add known bits handling.
+    if (OriginalDemandedBits.isSignMask()) {
+      APInt DemandedLHS, DemandedRHS;
+      getPackDemandedElts(VT, OriginalDemandedElts, DemandedLHS, DemandedRHS);
+
+      KnownBits KnownLHS, KnownRHS;
+      APInt SignMask = APInt::getSignMask(BitWidth * 2);
+      if (SimplifyDemandedBits(Op.getOperand(0), SignMask, DemandedLHS,
+                               KnownLHS, TLO, Depth + 1))
+        return true;
+      if (SimplifyDemandedBits(Op.getOperand(1), SignMask, DemandedRHS,
+                               KnownRHS, TLO, Depth + 1))
+        return true;
+    }
+    // TODO - add general PACKSS/PACKUS SimplifyDemandedBits support.
+    break;
   case X86ISD::PCMPGT:
     // icmp sgt(0, R) == ashr(R, BitWidth-1).
     // iff we only need the sign bit then we can use R directly.