fixes #25658; two overflowed *= causes program deadloop sysFatal on --exceptions:goto (#25660)

fixes #25658

tests/stdlib/tmisc_issues.nim

@@ -64,3 +64,120 @@ block: # bug #24683
         cast[ptr int](addr x)[] = 10
 
       doAssert x == @[1, 2, 3, 4, 45, 56, 67, 999, 88, 777]
+
+when not defined(js):
+  block:
+    var x = high int
+    var result = x
+
+    # assert that multiplying highest int by highest int overflows
+
+    doAssertRaises(OverflowDefect):
+      x *= x
+
+    doAssertRaises(OverflowDefect):
+      result *= x
+
+    # overflow via compound assignment on int
+    var a = high(int)
+    doAssertRaises(OverflowDefect):
+      a += 1
+
+    var b = low(int)
+    doAssertRaises(OverflowDefect):
+      b -= 1
+
+    var c = high(int)
+    doAssertRaises(OverflowDefect):
+      c *= 2
+
+    # add smaller signed types too
+    var a8 = high(int8)
+    doAssertRaises(OverflowDefect):
+      a8 += 1
+
+    var b8 = low(int8)
+    doAssertRaises(OverflowDefect):
+      b8 -= 1
+
+    var c8 = high(int8)
+    doAssertRaises(OverflowDefect):
+      c8 *= 2
+
+    var a16 = high(int16)
+    doAssertRaises(OverflowDefect):
+      a16 += 1
+
+    var b16 = low(int16)
+    doAssertRaises(OverflowDefect):
+      b16 -= 1
+
+    # arithmetic operations that can overflow (non-compound direct ops)
+    doAssertRaises(OverflowDefect):
+      discard high(int) + 1
+
+    doAssertRaises(OverflowDefect):
+      discard low(int) - 1
+
+    doAssertRaises(OverflowDefect):
+      discard high(int) * 2
+
+    doAssertRaises(OverflowDefect):
+      discard low(int) div -1
+
+    # int8 overflow for signed operations
+    doAssertRaises(OverflowDefect):
+      discard high(int8) + 1'i8
+
+    doAssertRaises(OverflowDefect):
+      discard low(int8) - 1'i8
+
+    doAssertRaises(OverflowDefect):
+      discard high(int8) * 2'i8
+
+    # enum overflow, from arithmetics.succ/pred
+    type E = enum eA, eB
+    doAssertRaises(OverflowDefect):
+      discard eB.succ
+    doAssertRaises(OverflowDefect):
+      discard eA.pred
+
+    # floating-point compound divide should produce inf (not raise by defect)
+    var f = 1.0
+    f /= 0.0
+    # 1.0/0.0 is inf, check not finite
+    #doAssert not f.isFinite     # `isFinite` not in this context, but avoid crash
+    # simple check ensures it mutated to a very large value
+    # (in Nim, `inf` is represented as 1e300*1e300; this compares as true)
+    doAssert f == 1.0 / 0.0
+
+    # Additional overflow cases across various integer widths
+    doAssertRaises(OverflowDefect):
+      discard high(int32) + 1'i32
+
+    doAssertRaises(OverflowDefect):
+      discard low(int32) - 1'i32
+
+    doAssertRaises(OverflowDefect):
+      discard high(int64) + 1'i64
+
+    doAssertRaises(OverflowDefect):
+      discard low(int64) - 1'i64
+
+    doAssertRaises(OverflowDefect):
+      discard -low(int64)
+
+    doAssertRaises(OverflowDefect):
+      discard abs(low(int8))
+
+    doAssertRaises(OverflowDefect):
+      discard high(int32) * 2'i32
+
+    doAssertRaises(OverflowDefect):
+      discard high(int64) * 2'i64
+
+    doAssertRaises(OverflowDefect):
+      discard low(int32) div -1'i32
+
+    doAssertRaises(OverflowDefect):
+      discard low(int64) div -1'i64