Add jtable instruction

* doc/ref/vm.texi (Instruction Set): Document new v32-x8-l24 instruction
  kind.
  (Branch Instructions): Document jtable.
* libguile/instructions.c (FOR_EACH_INSTRUCTION_WORD_TYPE): Add
  V32_X8_L24.
* libguile/jit.c (compile_jtable, compile_jtable_slow):
  (COMPILE_X8_S24__V32_X8_L24, analyze): Add stub JIT compiler
  implementation.
* libguile/vm-engine.c (jtable): New instruction.
* module/language/bytecode.scm (instruction-arity): Deprecate.
* module/system/vm/assembler.scm (encoder, assembler): Add V32_X8_L24
  case.
* module/system/vm/disassembler.scm (u32-ref, s32-ref): Move definitions
  to expansion-time only.
  (define-op-handlers): New definition, replacing visit-opcodes.
  (disassemblers, jump-parsers, stack-effect-parsers, clobber-parsers):
  Rework in terms of define-op-handlers.  Default case becomes #f, and
  add support for jtable.
  (disassemble-one, instruction-relative-jump-targets)
  (instruction-stack-size-after, instruction-slot-clobbers): Inline
  default case in the lookup procedure, not copied in the handler
  vector.
  (compute-labels): Add jtable case.
  (instruction-lengths-vector, instruction-length): Rework to allow
  variable-length instructions, and mark jtable as being
  variable-length.
  (instruction-has-fallthrough?): Add jtable to the no-fallthrough
  set.

1 files changed, 25 insertions, 1 deletions

diff --git a/libguile/vm-engine.c b/libguile/vm-engine.c
index 19d35f113..74825818d 100644
--- a/libguile/vm-engine.c
+++ b/libguile/vm-engine.c
@@ -3376,7 +3376,31 @@ VM_NAME (scm_thread *thread)
       NEXT (2);
     }
 
-  VM_DEFINE_OP (163, unused_163, NULL, NOP)
+  /* jtable idx:24 len:32 (_:8 offset:24)...
+   *
+   * Branch to an entry in a table, as in C's switch statement.  IDX is
+   * a u64 local, and the immediate LEN indicates the number of entries
+   * in the table, and should be greater than or equal to 1.  The last
+   * entry in the table is the "catch-all" entry.  The OFFSET... values
+   * are in the usual L24 encoding, indicating a memory address as a
+   * number of 32-bit words away from the current instruction pointer.
+   */
+  VM_DEFINE_OP (163, jtable, "jtable", OP2 (X8_S24, V32_X8_L24))
+    {
+      uint32_t idx, len;
+      const uint32_t *offsets;
+
+      UNPACK_24 (op, idx);
+      len = ip[1];
+      offsets = ip + 2;
+
+      uint64_t i = SP_REF_U64 (idx);
+      VM_ASSERT (len > 0, abort());
+      int32_t offset = offsets[i < len ? i : len - 1];
+      offset >>= 8; /* Sign-extending shift. */
+      NEXT (offset);
+    }
+
   VM_DEFINE_OP (164, unused_164, NULL, NOP)
   VM_DEFINE_OP (165, unused_165, NULL, NOP)
   VM_DEFINE_OP (166, unused_166, NULL, NOP)