[RISCV] Support Expressions in .insn Directives (llvm#111893)

When assembling raw instructions, often you want to or together several
fields for clarity, or because you're using an assembly macro with
separate arguments.

This brings the use of `.insn` closer into line with what can be done
with the binutils assembler.

The 64-bit instruction test here explicitly sets the top bit to make
sure this works, even though the assembler is really using `int64_t`
in most places internally.

llvm/lib/Target/RISCV/AsmParser/RISCVAsmParser.cpp

@@ -3172,12 +3172,11 @@ bool RISCVAsmParser::parseDirectiveInsn(SMLoc L) {
     // Try parsing .insn [ length , ] value
     std::optional<int64_t> Length;
     int64_t Value = 0;
-    if (Parser.parseIntToken(
-            Value, "expected instruction format or an integer constant"))
+    if (Parser.parseAbsoluteExpression(Value))
       return true;
     if (Parser.parseOptionalToken(AsmToken::Comma)) {
       Length = Value;
-      if (Parser.parseIntToken(Value, "expected an integer constant"))
+      if (Parser.parseAbsoluteExpression(Value))
         return true;
 
       if (*Length == 0 || (*Length % 2) != 0)

llvm/test/MC/RISCV/insn-invalid.s

@@ -24,8 +24,8 @@
 # Make fake mnemonics we use to match these in the tablegened asm match table isn't exposed.
 .insn_i  0x13,  0,  a0, a1, 13, 14 # CHECK: :[[@LINE]]:1: error: unknown directive
 
-.insn . # CHECK: :[[@LINE]]:7: error: expected instruction format or an integer constant
-.insn 0x2, # CHECK: :[[@LINE]]:12: error: expected an integer constant
+.insn . # CHECK: :[[@LINE]]:7: error: expected absolute expression
+.insn 0x2, # CHECK: :[[@LINE]]:12: error: unknown token in expression
 
 .insn 0x4, 0x13, 0 # CHECK: :[[@LINE]]:16: error: invalid operand for instruction
 
@@ -49,7 +49,10 @@
 .insn 0x2, 0x10001 # CHECK: :[[@LINE]]:7: error: encoding value does not fit into instruction
 .insn 0x4, 0x100000003 # CHECK: :[[@LINE]]:7: error: encoding value does not fit into instruction
 .insn 0x6, 0x100000000001f # CHECK: :[[@LINE]]:7: error: encoding value does not fit into instruction
-.insn 0x8, 0x1000000000000003f # CHECK: :[[@LINE]]:12: error: expected an integer constant
+.insn 0x8, 0x1000000000000003f # CHECK: :[[@LINE]]:12: error: literal value out of range for directive
 
 .insn 0x0010 # CHECK: :[[@LINE]]:7: error: compressed instructions are not allowed
 .insn 0x2, 0x0001 # CHECK: :[[@LINE]]:7: error: compressed instructions are not allowed
+
+.insn 0x2 + 0x2, 0x3 | (31 # CHECK: :[[@LINE]]:28: error: expected ')'
+.insn 0x4 * , 0xbf | (31 << 59) # CHECK: :[[@LINE]]:13: error: unknown token in expression

llvm/test/MC/RISCV/insn.s

@@ -185,6 +185,16 @@ target:
 # CHECK-OBJ: <unknown>
 .insn 0x8, 0xffffffffffffffbf
 
+# CHECK-ASM: .insn 0x4, 3971
+# CHECK-ASM: encoding: [0x83,0x0f,0x00,0x00]
+# CHECK-OBJ: lb t6, 0x0(zero)
+.insn 0x2 + 0x2, 0x3 | (31 << 7)
+
+# CHECK-ASM: .insn 0x8, -576460752303423297
+# CHECK-ASM: encoding: [0xbf,0x00,0x00,0x00,0x00,0x00,0x00,0xf8]
+# CHECK-OBJ: <unknown>
+.insn 0x4 * 0x2, 0xbf | (31 << 59)
+
 odd_lengths:
 # CHECK-ASM-LABEL: odd_lengths:
 # CHECK-OBJ-LABEL: <odd_lengths>: