AArch64: clamp UBFX high-bit to 32-bits

We were producing invalid instructions like "ubfx w0, w0, #20, #16".

Author: TNorthover

llvm/lib/Target/AArch64/AArch64ISelDAGToDAG.cpp

@@ -1852,6 +1852,7 @@ static bool isBitfieldExtractOpFromAnd(SelectionDAG *CurDAG, SDNode *N,
     VT = Opd0->getValueType(0);
   } else if (isOpcWithIntImmediate(Op0, ISD::SRL, SrlImm)) {
     Opd0 = Op0->getOperand(0);
+    ClampMSB = (VT == MVT::i32);
   } else if (BiggerPattern) {
     // Let's pretend a 0 shift right has been performed.
     // The resulting code will be at least as good as the original one

llvm/test/CodeGen/AArch64/bitfield.ll

@@ -230,3 +230,16 @@ define dso_local i64 @test_sbfx64(i64* %addr) {
    %extended = ashr i64 %shifted, 1
    ret i64 %extended
 }
+
+define i32 @test_ubfx_mask(i32 %lhs, i32 %rhs) {
+; CHECK-LABEL: test_ubfx_mask:
+; CHECK: lsr w0, w1, #20
+  %mask = and i32 %lhs, 20
+  %i7 = add i32 %mask, 1
+  %i8 = xor i32 %lhs, 20
+  %i9 = xor i32 %i8, %i7
+  %i10 = and i32 %i9, 20
+  %shift = lshr i32 %rhs, %i10
+  %shift.masked = and i32 %shift, 65535
+  ret i32 %shift.masked
+}