[clang] [llvm] [RISC-V][MC] Introduce initial support for RVY (CHERI) (PR #199771)

[Craig Topper via cfe-commits]

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@@ -239,6 +239,31 @@ static DecodeStatus DecodeTRM4RegisterClass(MCInst &Inst, uint32_t RegNo,
   return MCDisassembler::Success;
 }
 
+static DecodeStatus DecodeYBNDSWImm(MCInst &Inst, uint64_t Imm, int64_t Address,
+                                    const MCDisassembler *Decoder) {
+  assert(isUInt<9>(Imm) && "Invalid immediate");
+  uint64_t Result;
+  if (Imm == 0) {
+    // If imm[8:0] == 0, result is 4096.
+    Result = 4096;
+  } else if (Imm <= 255) {
+    // If imm[8] == 0 and imm[7:0] != 0, result is imm[7:0].
+    Result = Imm;
+  } else {
+    uint64_t Imm7To5 = (Imm & 0xFF) >> 5;
+    if (Imm7To5 == 0) {
+      // If imm[8] == 1 and imm[7:5] == 0, result is
+      // `256 | (imm[3:0] << 4) | (imm[4] << 3)`.
+      Result = 256 + ((Imm & 0xF) << 4) + (((Imm >> 4) & 1) << 3);
+    } else {
+      // Otherwise, result is imm[7:0] << 4.
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topperc wrote:

The next line uses `Imm7To5` which only contains bits 7:5 of immediate in its lsbs, right?

https://github.com/llvm/llvm-project/pull/199771