[AArch64AsmParser] Support (xxx), lsl 16 after #80571

An immediate integer operand not prefixed with # can also be followed
by "lsl". Parse "lsl".
In the wild, edk2 ArmPkg/Include/AsmMacroIoLibV8.h has
`movz      Reg, (Val) >> 16, lsl #16`.

Note: our support for paren expression not prefixed with # is not very
good. For example, `adds x3, x4, (1024>>0), lsl 12` fails to be parsed.

llvm/lib/Target/AArch64/AsmParser/AArch64AsmParser.cpp

@@ -4764,6 +4764,15 @@ bool AArch64AsmParser::parseOperand(OperandVector &Operands, bool isCondCode,
 
   // Nothing custom, so do general case parsing.
   SMLoc S, E;
+  auto parseOptionalShiftExtend = [&](AsmToken SavedTok) {
+    if (parseOptionalToken(AsmToken::Comma)) {
+      ParseStatus Res = tryParseOptionalShiftExtend(Operands);
+      if (!Res.isNoMatch())
+        return Res.isFailure();
+      getLexer().UnLex(SavedTok);
+    }
+    return false;
+  };
   switch (getLexer().getKind()) {
   default: {
     SMLoc S = getLoc();
@@ -4773,7 +4782,7 @@ bool AArch64AsmParser::parseOperand(OperandVector &Operands, bool isCondCode,
 
     SMLoc E = SMLoc::getFromPointer(getLoc().getPointer() - 1);
     Operands.push_back(AArch64Operand::CreateImm(Expr, S, E, getContext()));
-    return false;
+    return parseOptionalShiftExtend(getTok());
   }
   case AsmToken::LBrac: {
     Operands.push_back(
@@ -4895,14 +4904,7 @@ bool AArch64AsmParser::parseOperand(OperandVector &Operands, bool isCondCode,
     Operands.push_back(AArch64Operand::CreateImm(ImmVal, S, E, getContext()));
 
     // Parse an optional shift/extend modifier.
-    AsmToken SavedTok = Tok;
-    if (parseOptionalToken(AsmToken::Comma)) {
-      ParseStatus Res = tryParseOptionalShiftExtend(Operands);
-      if (!Res.isNoMatch())
-        return Res.isFailure();
-      getLexer().UnLex(SavedTok);
-    }
-    return false;
+    return parseOptionalShiftExtend(Tok);
   }
   case AsmToken::Equal: {
     SMLoc Loc = getLoc();

llvm/test/MC/AArch64/arm64-optional-hash.s

@@ -8,6 +8,10 @@
 ; CHECK: adds x3, x4, #1024, lsl #12 ; encoding: [0x83,0x00,0x50,0xb1]
 adds x3, x4, 1024, lsl 12
 
+; CHECK-COUNT-2: mov x3, #327680 ; encoding: [0xa3,0x00,0xa0,0xd2]
+movz x3, (0x54321) >> 16, lsl 16
+movz x3, (0x54321 >> 16), lsl 16
+
 ; Optional extend
 ; CHECK: add sp, x2, x3              ; encoding: [0x5f,0x60,0x23,0x8b]
 add sp, x2, x3, uxtx 0