[ARM] Add Neon shift instructions vshl, vshr.

src/arm/assembler-arm.cc

Index: src/arm/assembler-arm.cc
diff --git a/src/arm/assembler-arm.cc b/src/arm/assembler-arm.cc
index 6fef17b0b120039a72f5beef463c3ddf3092c28e..52213b06ccebc89d64b34939a0ebb730571f6828 100644
--- a/src/arm/assembler-arm.cc
+++ b/src/arm/assembler-arm.cc
@@ -4412,6 +4412,48 @@ void Assembler::vmax(NeonDataType dt, QwNeonRegister dst, QwNeonRegister src1,
   emit(EncodeNeonBinOp(VMAX, dt, dst, src1, src2));
 }
 
+enum NeonShiftOp { VSHL, VSHR };
+
+static Instr EncodeNeonShiftOp(NeonShiftOp op, NeonDataType dt,
+                               QwNeonRegister dst, QwNeonRegister src,
+                               int shift) {
+  int vd, d;
+  dst.split_code(&vd, &d);
+  int vm, m;
+  src.split_code(&vm, &m);
+  int size_in_bits = kBitsPerByte << NeonSz(dt);
+  int op_encoding = 0;
+  int imm6 = 0;
+  if (op == VSHL) {
+    DCHECK(shift >= 0 && size_in_bits > shift);
+    imm6 = size_in_bits + shift;
+    op_encoding = 0x5 * B8;
+  } else {
+    DCHECK_EQ(VSHR, op);
+    DCHECK(shift > 0 && size_in_bits >= shift);
+    imm6 = 2 * size_in_bits - shift;
+    op_encoding = NeonU(dt) * B24;
+  }
+  return 0x1E5U * B23 | d * B22 | imm6 * B16 | vd * B12 | B6 | m * B5 | B4 |
+         vm | op_encoding;
+}
+
+void Assembler::vshl(NeonDataType dt, QwNeonRegister dst, QwNeonRegister src,
+                     int shift) {
+  DCHECK(IsEnabled(NEON));
+  // Qd = vshl(Qm, bits) SIMD shift left immediate.
+  // Instruction details available in ARM DDI 0406C.b, A8-1046.
+  emit(EncodeNeonShiftOp(VSHL, dt, dst, src, shift));
+}
+
+void Assembler::vshr(NeonDataType dt, QwNeonRegister dst, QwNeonRegister src,
+                     int shift) {
+  DCHECK(IsEnabled(NEON));
+  // Qd = vshl(Qm, bits) SIMD shift right immediate.
+  // Instruction details available in ARM DDI 0406C.b, A8-1052.
+  emit(EncodeNeonShiftOp(VSHR, dt, dst, src, shift));
+}
+
 static Instr EncodeNeonEstimateOp(bool is_rsqrt, QwNeonRegister dst,
                                   QwNeonRegister src) {
   int vd, d;