[CHERI] Add enum values and LL parse/print support for CHERIoT calling conventions. (#156328)

This is the set of the calling conventions supported by the CHERIoT downstream of LLVM.

---------

Co-authored-by: Nikita Popov <github@npopov.com>

Author: resistor

llvm/include/llvm/AsmParser/LLToken.h

@@ -187,6 +187,9 @@ enum Kind {
   kw_graalcc,
   kw_riscv_vector_cc,
   kw_riscv_vls_cc,
+  kw_cheriot_compartmentcallcc,
+  kw_cheriot_compartmentcalleecc,
+  kw_cheriot_librarycallcc,
 
   // Attributes:
   kw_attributes,

llvm/include/llvm/IR/CallingConv.h

@@ -287,6 +287,16 @@ namespace CallingConv {
     // Calling convention for AMDGPU whole wave functions.
     AMDGPU_Gfx_WholeWave = 124,
 
+    /// Calling convention used for CHERIoT when crossing a protection boundary.
+    CHERIoT_CompartmentCall = 125,
+    /// Calling convention used for the callee of CHERIoT_CompartmentCall.
+    /// Ignores the first two capability arguments and the first integer
+    /// argument, zeroes all unused return registers on return.
+    CHERIoT_CompartmentCallee = 126,
+    /// Calling convention used for CHERIoT for cross-library calls to a
+    /// stateless compartment.
+    CHERIoT_LibraryCall = 127,
+
     /// The highest possible ID. Must be some 2^k - 1.
     MaxID = 1023
   };

llvm/lib/AsmParser/LLLexer.cpp

@@ -685,6 +685,9 @@ lltok::Kind LLLexer::LexIdentifier() {
   KEYWORD(graalcc);
   KEYWORD(riscv_vector_cc);
   KEYWORD(riscv_vls_cc);
+  KEYWORD(cheriot_compartmentcallcc);
+  KEYWORD(cheriot_compartmentcalleecc);
+  KEYWORD(cheriot_librarycallcc);
 
   KEYWORD(cc);
   KEYWORD(c);

llvm/lib/AsmParser/LLParser.cpp

@@ -2315,6 +2315,15 @@ bool LLParser::parseOptionalCallingConv(unsigned &CC) {
 #undef CC_VLS_CASE
     }
     return false;
+  case lltok::kw_cheriot_compartmentcallcc:
+    CC = CallingConv::CHERIoT_CompartmentCall;
+    break;
+  case lltok::kw_cheriot_compartmentcalleecc:
+    CC = CallingConv::CHERIoT_CompartmentCallee;
+    break;
+  case lltok::kw_cheriot_librarycallcc:
+    CC = CallingConv::CHERIoT_LibraryCall;
+    break;
   case lltok::kw_cc: {
       Lex.Lex();
       return parseUInt32(CC);

llvm/lib/IR/AsmWriter.cpp

@@ -430,6 +430,15 @@ static void PrintCallingConv(unsigned cc, raw_ostream &Out) {
     CC_VLS_CASE(32768)
     CC_VLS_CASE(65536)
 #undef CC_VLS_CASE
+  case CallingConv::CHERIoT_CompartmentCall:
+    Out << "cheriot_compartmentcallcc";
+    break;
+  case CallingConv::CHERIoT_CompartmentCallee:
+    Out << "cheriot_compartmentcalleecc";
+    break;
+  case CallingConv::CHERIoT_LibraryCall:
+    Out << "cheriot_librarycallcc";
+    break;
   }
 }