[TargetLowering] SimplifyDemandedBits - just call computeKnownBits for BUILD_VECTOR cases.

Don't do this locally, computeKnownBits does this better (and can handle non-constant cases as well).

A next step would be to actually simplify non-constant elements - building on what we already do in SimplifyDemandedVectorElts.

llvm-svn: 365309

Author: RKSimon

llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp

@@ -639,29 +639,9 @@ bool TargetLowering::SimplifyDemandedBits(
     break;
   }
   case ISD::BUILD_VECTOR:
-    // Collect the known bits that are shared by every constant vector element.
-    Known.Zero.setAllBits(); Known.One.setAllBits();
-    for (SDValue SrcOp : Op->ops()) {
-      if (!isa<ConstantSDNode>(SrcOp)) {
-        // We can only handle all constant values - bail out with no known bits.
-        Known = KnownBits(BitWidth);
-        return false;
-      }
-      Known2.One = cast<ConstantSDNode>(SrcOp)->getAPIntValue();
-      Known2.Zero = ~Known2.One;
-
-      // BUILD_VECTOR can implicitly truncate sources, we must handle this.
-      if (Known2.One.getBitWidth() != BitWidth) {
-        assert(Known2.getBitWidth() > BitWidth &&
-               "Expected BUILD_VECTOR implicit truncation");
-        Known2 = Known2.trunc(BitWidth);
-      }
-
-      // Known bits are the values that are shared by every element.
-      // TODO: support per-element known bits.
-      Known.One &= Known2.One;
-      Known.Zero &= Known2.Zero;
-    }
+    // Collect the known bits that are shared by every demanded element.
+    // TODO: Call SimplifyDemandedBits for non-constant demanded elements.
+    Known = TLO.DAG.computeKnownBits(Op, DemandedElts, Depth);
     return false; // Don't fall through, will infinitely loop.
   case ISD::LOAD: {
     LoadSDNode *LD = cast<LoadSDNode>(Op);