[llvm] [RISCV][MC] Add support for hardcode encoding of .insn directive (PR #98030)

[Craig Topper via llvm-commits]

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@@ -3055,17 +3057,49 @@ bool isValidInsnFormat(StringRef Format, bool AllowC) {
 
 /// parseDirectiveInsn
 /// ::= .insn [ format encoding, (operands (, operands)*) ]
+/// ::= .insn [ length, value ]
+/// ::= .insn [ value ]
 bool RISCVAsmParser::parseDirectiveInsn(SMLoc L) {
   MCAsmParser &Parser = getParser();
 
+  bool AllowC = getSTI().hasFeature(RISCV::FeatureStdExtC) ||
+                getSTI().hasFeature(RISCV::FeatureStdExtZca);
+
   // Expect instruction format as identifier.
   StringRef Format;
   SMLoc ErrorLoc = Parser.getTok().getLoc();
-  if (Parser.parseIdentifier(Format))
-    return Error(ErrorLoc, "expected instruction format");
+  if (Parser.parseIdentifier(Format)) {
+    // Try parsing .insn [length], value
+    int64_t Length = 0;
+    int64_t Value = 0;
+    if (Parser.parseIntToken(
+            Value, "expected instruction format or an integer constant"))
+      return true;
+    if (Parser.parseOptionalToken(AsmToken::Comma)) {
+      Length = Value;
+      if (Parser.parseIntToken(Value, "expected an integer constant"))
+        return true;
+    }
+
+    int64_t RealLength = (Value & 3) == 3 ? 4 : 2;
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topperc wrote:

Can this be `unsigned`?

https://github.com/llvm/llvm-project/pull/98030