1 files changed, 14 insertions, 0 deletions
diff --git a/llvm/lib/Target/AMDGPU/AMDGPUISelLowering.cpp b/llvm/lib/Target/AMDGPU/AMDGPUISelLowering.cpp
index bb08fd2f54a..0ec338e2e12 100644
--- a/llvm/lib/Target/AMDGPU/AMDGPUISelLowering.cpp
+++ b/llvm/lib/Target/AMDGPU/AMDGPUISelLowering.cpp
@@ -4084,6 +4084,20 @@ void AMDGPUTargetLowering::computeKnownBitsForTargetNode(
       Known.Zero.setHighBits(32 - MaxValBits);
     break;
   }
+  case ISD::INTRINSIC_WO_CHAIN: {
+    unsigned IID = cast<ConstantSDNode>(Op.getOperand(0))->getZExtValue();
+    switch (IID) {
+    case Intrinsic::amdgcn_mbcnt_lo:
+    case Intrinsic::amdgcn_mbcnt_hi: {
+      // These return at most the wavefront size - 1.
+      unsigned Size = Op.getValueType().getSizeInBits();
+      Known.Zero.setHighBits(Size - Subtarget->getWavefrontSizeLog2());
+      break;
+    }
+    default:
+      break;
+    }
+  }
   }
 }