From f1c44eb4a28e6ae957239af56ca84064963492b9 Mon Sep 17 00:00:00 2001
From: Nick Gasson <nick@nickg.me.uk>
Date: Thu, 17 Nov 2022 21:04:27 +0000
Subject: [PATCH] Add peephole optimisations for SUB opcode

---
 src/jit/jit-core.c  |  2 ++
 src/jit/jit-optim.c | 20 ++++++++++++++++++++
 test/test_jit.c     | 11 +++++++++++
 3 files changed, 33 insertions(+)

diff --git a/src/jit/jit-core.c b/src/jit/jit-core.c
index bc0435f0..d38668b3 100644
--- a/src/jit/jit-core.c
+++ b/src/jit/jit-core.c
@@ -1062,6 +1062,8 @@ jit_handle_t jit_assemble(jit_t *j, ident_t name, const char *text)
       { "T",  JIT_CC_T },
       { "F",  JIT_CC_F },
       { "EQ", JIT_CC_EQ },
+      { "O",  JIT_CC_O },
+      { "C",  JIT_CC_C },
    };
 
    f->bufsz = 128;
diff --git a/src/jit/jit-optim.c b/src/jit/jit-optim.c
index 00d9a80b..a1ca2936 100644
--- a/src/jit/jit-optim.c
+++ b/src/jit/jit-optim.c
@@ -497,6 +497,19 @@ static void jit_lvn_sub(jit_ir_t *ir, lvn_state_t *state)
 #undef FOLD_SUB
    }
 
+   if (ir->arg2.kind == JIT_VALUE_INT64 && ir->arg2.int64 == 0) {
+      lvn_mov_reg(ir, state, ir->arg1.reg);
+      return;
+   }
+   else if (ir->arg1.kind == JIT_VALUE_INT64 && ir->arg1.int64 == 0
+            && ir->cc == JIT_CC_NONE && ir->size == JIT_SZ_UNSPEC) {
+     ir->op        = J_NEG;
+     ir->arg1      = ir->arg2;
+     ir->arg2.kind = JIT_VALUE_INVALID;
+     jit_lvn_generic(ir, state);
+     return;
+   }
+
    jit_lvn_generic(ir, state);
 }
 
@@ -519,6 +532,12 @@ static void jit_lvn_copy(jit_ir_t *ir, lvn_state_t *state)
    state->regvn[ir->result] = state->nextvn++;
 }
 
+static void jit_lvn_bzero(jit_ir_t *ir, lvn_state_t *state)
+{
+   // Clobbers the count register
+   state->regvn[ir->result] = state->nextvn++;
+}
+
 void jit_do_lvn(jit_func_t *f)
 {
    lvn_state_t state = {
@@ -546,6 +565,7 @@ void jit_do_lvn(jit_func_t *f)
          case J_SUB: jit_lvn_sub(ir, &state); break;
          case J_MOV: jit_lvn_mov(ir, &state); break;
          case MACRO_COPY: jit_lvn_copy(ir, &state); break;
+         case MACRO_BZERO: jit_lvn_bzero(ir, &state); break;
          default: break;
          }
       }
diff --git a/test/test_jit.c b/test/test_jit.c
index 132a549a..672927fd 100644
--- a/test/test_jit.c
+++ b/test/test_jit.c
@@ -1298,6 +1298,9 @@ START_TEST(test_lvn1)
       "    MUL     R1, #1, R2    \n"
       "    MUL     R1, #0, R2    \n"
       "    ADD     R1, R1, #0    \n"
+      "    SUB     R1, R1, #0    \n"
+      "    SUB     R1, #0, R1    \n"
+      "    SUB.O   R1, #0, R1    \n"
       "    RET                   \n";
 
    jit_handle_t h1 = jit_assemble(j, ident_new("myfunc"), text1);
@@ -1335,6 +1338,14 @@ START_TEST(test_lvn1)
 
    ck_assert_int_eq(f->irbuf[12].op, J_NOP);
 
+   ck_assert_int_eq(f->irbuf[13].op, J_NOP);
+
+   ck_assert_int_eq(f->irbuf[14].op, J_NEG);
+   ck_assert_int_eq(f->irbuf[14].arg1.kind, JIT_VALUE_REG);
+   ck_assert_int_eq(f->irbuf[14].arg1.reg, 1);
+
+   ck_assert_int_eq(f->irbuf[15].op, J_SUB);
+
    jit_free(j);
 }
 END_TEST
-- 
2.39.2