From 625e9451a75b3094597a1b1647cb71fa65bd8b98 Mon Sep 17 00:00:00 2001
From: Andrew Waterman <andrew@sifive.com>
Date: Mon, 10 Jun 2024 18:30:34 -0700
Subject: Keep potentially overlapping instructions in order at head of list

---
 riscv/processor.cc | 52 ++++++++++++++++++++++++++++++++--------------------
 1 file changed, 32 insertions(+), 20 deletions(-)

diff --git a/riscv/processor.cc b/riscv/processor.cc
index 3a9c0d9..c8cb5be 100644
--- a/riscv/processor.cc
+++ b/riscv/processor.cc
@@ -1111,17 +1111,6 @@ void processor_t::register_insn(insn_desc_t desc, bool is_custom) {
 
 void processor_t::build_opcode_map()
 {
-  struct cmp {
-    bool operator()(const insn_desc_t& lhs, const insn_desc_t& rhs) {
-      if (lhs.match == rhs.match)
-        return lhs.mask > rhs.mask;
-      return lhs.match > rhs.match;
-    }
-  };
-
-  std::sort(instructions.begin(), instructions.end(), cmp());
-  std::sort(custom_instructions.begin(), custom_instructions.end(), cmp());
-
   for (size_t i = 0; i < OPCODE_CACHE_SIZE; i++)
     opcode_cache[i] = insn_desc_t::illegal();
 }
@@ -1145,15 +1134,12 @@ void processor_t::register_base_instructions()
 {
   #define DECLARE_INSN(name, match, mask) \
     insn_bits_t name##_match = (match), name##_mask = (mask); \
-    bool name##_supported = true;
+    isa_extension_t name##_ext = NUM_ISA_EXTENSIONS; \
+    bool name##_overlapping = false;
 
   #include "encoding.h"
   #undef DECLARE_INSN
 
-  #define DECLARE_OVERLAP_INSN(name, ext) { name##_supported = isa->extension_enabled(ext); }
-  #include "overlap_list.h"
-  #undef DECLARE_OVERLAP_INSN
-
   #define DEFINE_INSN(name) \
     extern reg_t fast_rv32i_##name(processor_t*, insn_t, reg_t); \
     extern reg_t fast_rv64i_##name(processor_t*, insn_t, reg_t); \
@@ -1162,8 +1148,14 @@ void processor_t::register_base_instructions()
     extern reg_t logged_rv32i_##name(processor_t*, insn_t, reg_t); \
     extern reg_t logged_rv64i_##name(processor_t*, insn_t, reg_t); \
     extern reg_t logged_rv32e_##name(processor_t*, insn_t, reg_t); \
-    extern reg_t logged_rv64e_##name(processor_t*, insn_t, reg_t); \
-    if (name##_supported) { \
+    extern reg_t logged_rv64e_##name(processor_t*, insn_t, reg_t);
+  #include "insn_list.h"
+  #undef DEFINE_INSN
+
+  // add overlapping instructions first, in order
+  #define DECLARE_OVERLAP_INSN(name, ext) \
+    name##_overlapping = true; \
+    if (isa->extension_enabled(ext)) \
       register_base_insn((insn_desc_t) { \
         name##_match, \
         name##_mask, \
@@ -1174,9 +1166,29 @@ void processor_t::register_base_instructions()
         logged_rv32i_##name, \
         logged_rv64i_##name, \
         logged_rv32e_##name, \
-        logged_rv64e_##name}); \
-    }
+        logged_rv64e_##name});
+  #include "overlap_list.h"
+  #undef DECLARE_OVERLAP_INSN
+
+  // add all other instructions.  since they are non-overlapping, the order
+  // does not affect correctness, but more frequent instructions should
+  // appear earlier to improve search time on opcode_cache misses.
+  #define DEFINE_INSN(name) \
+    if (!name##_overlapping) \
+      register_base_insn((insn_desc_t) { \
+        name##_match, \
+        name##_mask, \
+        fast_rv32i_##name, \
+        fast_rv64i_##name, \
+        fast_rv32e_##name, \
+        fast_rv64e_##name, \
+        logged_rv32i_##name, \
+        logged_rv64i_##name, \
+        logged_rv32e_##name, \
+        logged_rv64e_##name});
   #include "insn_list.h"
+  #undef DEFINE_INSN
+
   // terminate instruction list with a catch-all
   register_base_insn(insn_desc_t::illegal());
 
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