From 2ed80d1921252798cf83d82de5da159c71ebcac1 Mon Sep 17 00:00:00 2001
From: araq <araq4k@proton.me>
Date: Thu, 12 Mar 2026 14:24:50 +0100
Subject: [PATCH] now bootstraps with -d:nimsso

---
 compiler/layeredtable.nim | 11 +++++------
 lib/system/strs_v3.nim    |  4 +++-
 2 files changed, 8 insertions(+), 7 deletions(-)

diff --git a/compiler/layeredtable.nim b/compiler/layeredtable.nim
index 81c6c63d75..a2f958769b 100644
--- a/compiler/layeredtable.nim
+++ b/compiler/layeredtable.nim
@@ -46,12 +46,11 @@ proc setToPreviousLayer*(pt: var LayeredIdTable) {.inline.} =
   when useRef:
     pt = pt.nextLayer
   else:
-    when defined(gcDestructors):
-      pt = pt.nextLayer[]
-    else:
-      # workaround refc
-      let tmp = pt.nextLayer[]
-      pt = tmp
+    # Must read nextLayer into a temp before destroying pt:
+    # `pt = pt.nextLayer[]` would call eqcopy(&pt, &(*pt.nextLayer)) which
+    # decrements pt.nextLayer's rc (freeing it) before reading pt.nextLayer.nextLayer.
+    let tmp = pt.nextLayer[]
+    pt = tmp
 
 iterator pairs*(pt: LayeredIdTable): (ItemId, PType) =
   var tm = pt
diff --git a/lib/system/strs_v3.nim b/lib/system/strs_v3.nim
index 81c52d3134..14b495f629 100644
--- a/lib/system/strs_v3.nim
+++ b/lib/system/strs_v3.nim
@@ -133,7 +133,9 @@ proc ensureUniqueLong(s: var SmallString; oldLen, newLen: int) =
   if isHeap and s.more.rc == 1 and newLen <= cap:
     s.more.fullLen = newLen
   else:
-    let newCap = max(newLen, resize(cap))
+    # Only grow capacity when actually needed; pure COW copies (newLen <= cap)
+    # preserve the existing capacity to avoid exponential growth via repeated COW.
+    let newCap = if newLen > cap: max(newLen, resize(cap)) else: cap
     let p = cast[ptr LongString](alloc(sizeof(int) * 3 + newCap + 1))
     p.rc = 1
     p.fullLen = newLen