From bd063113ec3c00d80fc32a5581ac9552682f6b43 Mon Sep 17 00:00:00 2001
From: ringabout <43030857+ringabout@users.noreply.github.com>
Date: Fri, 26 Jul 2024 20:50:59 +0800
Subject: [PATCH] fixes #23894; succ/pred shouldn't raise OverflowDefect for
 unsigned integers (#23895)

fixes #23894

keeps it consistent with `inc`
---
 compiler/ccgexprs.nim         | 2 +-
 tests/system/tsystem_misc.nim | 6 ++++++
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/compiler/ccgexprs.nim b/compiler/ccgexprs.nim
index af3c8bf66e..17f2159495 100644
--- a/compiler/ccgexprs.nim
+++ b/compiler/ccgexprs.nim
@@ -590,7 +590,7 @@ proc binaryArithOverflow(p: BProc, e: PNode, d: var TLoc, m: TMagic) =
   # skipping 'range' is correct here as we'll generate a proper range check
   # later via 'chckRange'
   let t = e.typ.skipTypes(abstractRange)
-  if optOverflowCheck notin p.options:
+  if optOverflowCheck notin p.options or (m in {mSucc, mPred} and t.kind in {tyUInt..tyUInt64}):
     let res = "($1)($2 $3 $4)" % [getTypeDesc(p.module, e.typ), rdLoc(a), rope(opr[m]), rdLoc(b)]
     putIntoDest(p, d, e, res)
   else:
diff --git a/tests/system/tsystem_misc.nim b/tests/system/tsystem_misc.nim
index c8e2b2a9df..1debb7c48c 100644
--- a/tests/system/tsystem_misc.nim
+++ b/tests/system/tsystem_misc.nim
@@ -219,3 +219,9 @@ proc bug23223 = # bug #23223
   doAssert stuff == "hello"
 
 bug23223()
+
+block: # bug #23894
+  let v = high(uint) div 2
+  let s = v + 1 # 9223372036854775808
+  let m = succ v
+  doAssert s == m