fixes #10886 [backport] (#10897)

compiler/vmgen.nim

@@ -388,16 +388,28 @@ proc genIf(c: PCtx, n: PNode; dest: var TDest) =
   for endPos in endings: c.patch(endPos)
   c.clearDest(n, dest)
 
+proc isTemp(c: PCtx; dest: TDest): bool =
+  result = dest >= 0 and c.prc.slots[dest].kind >= slotTempUnknown
+
 proc genAndOr(c: PCtx; n: PNode; opc: TOpcode; dest: var TDest) =
   #   asgn dest, a
   #   tjmp|fjmp L1
   #   asgn dest, b
   # L1:
-  if dest < 0: dest = getTemp(c, n.typ)
+  let copyBack = dest < 0 or not isTemp(c, dest)
-  c.gen(n.sons[1], dest)
+  let tmp = if copyBack:
-  let L1 = c.xjmp(n, opc, dest)
+              getTemp(c, n.typ)
-  c.gen(n.sons[2], dest)
+            else:
+              TRegister dest
+  c.gen(n.sons[1], tmp)
+  let L1 = c.xjmp(n, opc, tmp)
+  c.gen(n.sons[2], tmp)
   c.patch(L1)
+  if dest < 0:
+    dest = tmp
+  elif copyBack:
+    c.gABC(n, opcAsgnInt, dest, tmp)
+    freeTemp(c, tmp)
 
 proc canonValue*(n: PNode): PNode =
   result = n
@@ -1469,9 +1481,6 @@ proc checkCanEval(c: PCtx; n: PNode) =
                   skIterator} and sfForward in s.flags:
     cannotEval(c, n)
 
-proc isTemp(c: PCtx; dest: TDest): bool =
-  result = dest >= 0 and c.prc.slots[dest].kind >= slotTempUnknown
-
 template needsAdditionalCopy(n): untyped =
   not c.isTemp(dest) and not fitsRegister(n.typ)
 

tests/vm/tvmmisc.nim

@@ -160,3 +160,21 @@ block:
       ["", "M", "MM", "MMM", "--", "-", "--", "---", "----", "--"],
     ]
   doAssert encoding.len == 4
+
+# #10886
+
+proc tor(): bool =
+  result = true
+  result = false or result
+
+proc tand(): bool =
+  result = false
+  result = true and result
+
+const
+  ctor = tor()
+  ctand = not tand()
+
+static:
+  doAssert ctor
+  doAssert ctand