[KnownBits] Mark constructor for KnownBits as explicit (llvm#190253)

To avoid confusion between constant values and bit widths.

Author: MaxGraey

llvm/include/llvm/CodeGen/FunctionLoweringInfo.h

@@ -162,9 +162,9 @@ class FunctionLoweringInfo {
   struct LiveOutInfo {
     unsigned NumSignBits : 31;
     unsigned IsValid : 1;
-    KnownBits Known = 1;
+    KnownBits Known;
 
-    LiveOutInfo() : NumSignBits(0), IsValid(true) {}
+    LiveOutInfo() : NumSignBits(0), IsValid(true), Known(1) {}
   };
 
   /// Record the preferred extend type (ISD::SIGN_EXTEND or ISD::ZERO_EXTEND)

llvm/include/llvm/Support/KnownBits.h

@@ -38,7 +38,7 @@ struct KnownBits {
   KnownBits() = default;
 
   /// Create a known bits object of BitWidth bits initialized to unknown.
-  KnownBits(unsigned BitWidth) : Zero(BitWidth, 0), One(BitWidth, 0) {}
+  explicit KnownBits(unsigned BitWidth) : Zero(BitWidth, 0), One(BitWidth, 0) {}
 
   /// Get the bit width of this value.
   unsigned getBitWidth() const {

llvm/lib/Target/NVPTX/NVPTXISelLowering.cpp

@@ -7673,7 +7673,7 @@ static void computeKnownBitsForPRMT(const SDValue Op, KnownBits &Known,
     unsigned Sign = Sel.getHiBits(1).getZExtValue();
     KnownBits Byte = BitField.extractBits(8, Idx * 8);
     if (Sign)
-      Byte = KnownBits::ashr(Byte, 8);
+      Byte = KnownBits::ashr(Byte, KnownBits::makeConstant(APInt(8, 7)));
     Known.insertBits(Byte, I * 8);
   }
 }