[llvm] [LLVM][MC][DecoderEmitter] Add support to specialize decoder per bitwidth (PR #154865)

[Craig Topper via llvm-commits]

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@@ -0,0 +1,175 @@
+// RUN: llvm-tblgen -gen-disassembler -I %p/../../include %s | FileCheck %s --check-prefix=CHECK-DEFAULT
+// RUN: llvm-tblgen -gen-disassembler -specialize-decoders-per-bitwidth -I %p/../../include %s | FileCheck %s --check-prefix=CHECK-SPECIALIZE-NO-TABLE
+// RUN: llvm-tblgen -gen-disassembler -specialize-decoders-per-bitwidth -use-fn-table-in-decode-to-mcinst -I %p/../../include %s | FileCheck %s --check-prefix=CHECK-SPECIALIZE-TABLE
+
+
+include "llvm/Target/Target.td"
+
+def archInstrInfo : InstrInfo { }
+
+def arch : Target {
+  let InstructionSet = archInstrInfo;
+}
+
+let Namespace = "arch" in {
+  def R0 : Register<"r0">;
+  def R1 : Register<"r1">;
+  def R2 : Register<"r2">;
+  def R3 : Register<"r3">;
+}
+def Regs : RegisterClass<"Regs", [i32], 32, (add R0, R1, R2, R3)>;
+
+// Bit 0 of the encoding determines the size (8 or 16 bits).
+// Bits {3..1} define the number define the number of operands encoded.
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topperc wrote:

"define the number" appears twice in this comment.

https://github.com/llvm/llvm-project/pull/154865