From 771554e39c047eec8e0451c5d8d7adbf990d356c Mon Sep 17 00:00:00 2001
From: lemon <lsof@mailbox.org>
Date: Sat, 20 Dec 2025 17:42:30 +0100
Subject: backend: general simplification pass skeleton

---
 ir/simpl.c | 146 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 146 insertions(+)
 create mode 100644 ir/simpl.c

(limited to 'ir/simpl.c')

diff --git a/ir/simpl.c b/ir/simpl.c
new file mode 100644
index 0000000..fb89c07
--- /dev/null
+++ b/ir/simpl.c
@@ -0,0 +1,146 @@
+#include "ir.h"
+
+static int
+ins(struct function *fn, struct instr *ins, struct block *blk, int *curi)
+{
+   int narg = opnarg[ins->op];
+   if ((oisarith(ins->op) || oiscmp(ins->op)) && isnumcon(ins->l) && (narg == 1 || isnumcon(ins->r))) {
+      bool ok;
+      if (narg == 1) ok = foldunop(&ins->l, ins->op, ins->cls, ins->l);
+      else ok = foldbinop(&ins->l, ins->op, ins->cls, ins->l, ins->r);
+      if (!ok) return 0; /* could be div/0 */
+      ins->op = Ocopy;
+      ins->cls = insrescls(*ins);
+      ins->r = NOREF;
+      return 1;
+   }
+   return 0;
+}
+
+static void
+jmpfind(struct block **final, struct block **pblk)
+{
+   struct block **p2 = &final[(*pblk)->id];
+   if (*p2 && !(*p2)->phi.n) {
+      jmpfind(final, p2);
+      *pblk = *p2;
+   }
+}
+
+static void
+fillpredsrec(struct block *blk)
+{
+   while (blk && !wasvisited(blk)) {
+      markvisited(blk);
+      if (!blk->s1) return;
+      if (!blk->s1->phi.n) addpred(blk->s1, blk);
+      if (!blk->s2) {
+         blk = blk->s1;
+         continue;
+      }
+      if (!blk->s2->phi.n) addpred(blk->s2, blk);
+      fillpredsrec(blk->s1);
+      blk = blk->s2;
+   }
+}
+
+static void
+fillpreds(struct function *fn)
+{
+   struct block *blk = fn->entry, *next;
+   do {
+      if (blk->phi.n) continue;
+      if (blk->npred > 1)
+         xbfree(blk->_pred);
+      blk->npred = 0;
+      blk->_pred = NULL;
+   } while ((blk = blk->lnext) != fn->entry);
+   startbbvisit();
+   fillpredsrec(fn->entry);
+   blk = fn->entry->lnext;
+   do { /* remove dead blocks */
+      next = blk->lnext;
+      if (!blk->npred) freeblk(fn, blk);
+   } while ((blk = next) != fn->entry);
+}
+
+void
+simpl(struct function *fn)
+{
+   FREQUIRE(FNUSE);
+   int inschange = 0,
+       blkchange = 0;
+   struct block **jmpfinal = xcalloc(fn->nblk * sizeof *jmpfinal);
+   struct block *blk = fn->entry;
+
+   do {
+      for (int i = 0; i < blk->phi.n; ++i) {
+
+      }
+      for (int i = 0; i < blk->ins.n; ++i) {
+         inschange += ins(fn, &instrtab[blk->ins.p[i]], blk, &i);
+      }
+
+      /* merge blocks:
+       * @blk:
+       *   ... (1)
+       *   b @s
+       * @s:
+       *   ... (2)
+       *   b {...}
+       *=>
+       * @blk:
+       *   ... (1)
+       *   ... (2)
+       *   b {...}
+       * */
+      if (blk != fn->entry) while (blk->s1 && !blk->s2 && blk->s1->npred == 1 && !blk->phi.n) {
+         struct block *s = blk->s1;
+         vpushn(&blk->ins, s->ins.p, s->ins.n);
+         blk->jmp = blk->s1->jmp;
+         for (int i = 0; i < 2; ++i) {
+            struct block *ss = (&s->s1)[i];
+            if (ss) for (int j = 0; j < ss->npred; ++j) {
+               if (blkpred(ss, j) == s) {
+                  blkpred(ss, j) = blk;
+                  break;
+               }
+            }
+         }
+         /* breaks use for temps used in s */
+         if (s->ins.n || s->jmp.arg[0].t == RTMP || s->jmp.arg[1].t == RTMP)
+            fn->prop &= ~FNUSE;
+         blk->s1 = s->s1;
+         blk->s2 = s->s2;
+         freeblk(fn, s);
+      }
+      /* thread jumps.. */
+      if (!blk->phi.n && !blk->ins.n) {
+         if (blk->jmp.t == Jb && !blk->s2) {
+            jmpfind(jmpfinal, &blk->s1);
+            if (blk->s1 != blk) {
+               ++blkchange;
+               jmpfinal[blk->id] = blk->s1;
+            }
+         }
+      }
+   } while ((blk = blk->lnext) != fn->entry);
+   if (inschange) {
+      if (!(fn->prop & FNUSE)) filluses(fn);
+      copyopt(fn);
+   }
+   if (blkchange) {
+      do {
+         if (blk->s1) jmpfind(jmpfinal, &blk->s1);
+         if (blk->s2) jmpfind(jmpfinal, &blk->s2);
+         if (blk->s1 && blk->s1 == blk->s2) {
+            memset(blk->jmp.arg, 0, sizeof blk->jmp.arg);
+            blk->s2 = NULL;
+         }
+      } while ((blk = blk->lnext) != fn->entry);
+      fillpreds(fn);
+   }
+   free(jmpfinal);
+}
+
+/* vim:set ts=3 sw=3 expandtab: */
-- 
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