From 7036e19098c295a075f97cbd056fdc43bd490fb2 Mon Sep 17 00:00:00 2001
From: lemon <lsof@mailbox.org>
Date: Tue, 23 Dec 2025 11:36:51 +0100
Subject: lower alloca as a separate pass before isel

---
 ir/dump.c  |  3 +++
 ir/ir.c    |  2 ++
 ir/ir.h    |  4 ++++
 ir/stack.c | 37 +++++++++++++++++++++++++++++++++++++
 4 files changed, 46 insertions(+)
 create mode 100644 ir/stack.c

(limited to 'ir')

diff --git a/ir/dump.c b/ir/dump.c
index a2faf27..f952292 100644
--- a/ir/dump.c
+++ b/ir/dump.c
@@ -155,6 +155,9 @@ dumpref(enum op o, union ref ref)
          bfmt(out, "]");
       }
       break;
+   case RSTACK:
+      bfmt(out, "[stack %d]", ref.i);
+      break;
    default: assert(!"ref");
    }
 }
diff --git a/ir/ir.c b/ir/ir.c
index 3c76cde..6edc429 100644
--- a/ir/ir.c
+++ b/ir/ir.c
@@ -650,6 +650,8 @@ irfini(struct function *fn)
       simpl(fn);
       freearena(fn->passarena);
    }
+   lowerstack(fn);
+   freearena(fn->passarena);
    if (ccopt.dbg.o) {
       bfmt(ccopt.dbgout, "<< Before isel >>\n");
       irdump(fn);
diff --git a/ir/ir.h b/ir/ir.h
index dccca0c..4248016 100644
--- a/ir/ir.h
+++ b/ir/ir.h
@@ -62,6 +62,7 @@ enum refkind {
    RXCON, /* other constants (incl. external symbols) */
    RADDR, /* target-specific addressing mode */
    RTYPE, /* irtype */
+   RSTACK, /* stack base offset */
 };
 
 union ref {
@@ -325,6 +326,9 @@ void mem2reg(struct function *);
 /** intrin.c **/
 void lowerintrin(struct function *);
 
+/** stack.c **/
+void lowerstack(struct function *);
+
 /** regalloc.c **/
 void regalloc(struct function *);
 
diff --git a/ir/stack.c b/ir/stack.c
new file mode 100644
index 0000000..2420fdb
--- /dev/null
+++ b/ir/stack.c
@@ -0,0 +1,37 @@
+#include "ir.h"
+
+void
+lowerstack(struct function *fn)
+{
+   extern int ninstr;
+   fn->stksiz = 0;
+   FREQUIRE(FNUSE);
+
+   struct block *blk = fn->entry;
+   do {
+      for (int i = 0; i < blk->ins.n; ++i) {
+         uint alignlog2, siz;
+         int t = blk->ins.p[i];
+         struct instr *ins = &instrtab[t];
+         switch (ins->op) {
+         case Oalloca1: case Oalloca2: case Oalloca4: case Oalloca8: case Oalloca16:
+            alignlog2 = ins->op - Oalloca1;
+            assert(ins->l.i > 0);
+            siz = ins->l.i << alignlog2;
+            fn->stksiz += siz;
+            fn->stksiz = alignup(fn->stksiz, 1 << alignlog2);
+            if (fn->stksiz > (1<<16)-1) error(NULL, "'%s' stack frame too big", fn->name);
+            *ins = mkinstr(Onop,0,);
+            replcuses(mkref(RTMP, t), mkref(RSTACK, fn->stksiz));
+            continue;
+         }
+      }
+   } while ((blk = blk->lnext) != fn->entry);
+
+   if (ccopt.dbg.s) {
+      bfmt(ccopt.dbgout, "<< After stack >>\n");
+      irdump(fn);
+   }
+}
+
+/* vim:set ts=3 sw=3 expandtab: */
-- 
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