From e3b5f80a890428a0c9b5c2bdd7a3205d79946957 Mon Sep 17 00:00:00 2001
From: Andreas Rumpf <rumpf_a@web.de>
Date: Thu, 24 Sep 2020 22:07:23 +0200
Subject: [PATCH] more precise borrow checking of 'result' (#15406)

---
 compiler/sempass2.nim      | 2 +-
 compiler/varpartitions.nim | 9 +++++++--
 2 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/compiler/sempass2.nim b/compiler/sempass2.nim
index d6db0885ef..797aff7f71 100644
--- a/compiler/sempass2.nim
+++ b/compiler/sempass2.nim
@@ -1248,7 +1248,7 @@ proc trackProc*(c: PContext; s: PSym, body: PNode) =
     if not t.hasSideEffect and t.hasDangerousAssign:
       t.hasSideEffect = varpartitions.hasSideEffect(partitions, mutationInfo)
     if views in c.features:
-      checkBorrowedLocations(partitions, g.config)
+      checkBorrowedLocations(partitions, body, g.config)
 
   if sfThread in s.flags and t.gcUnsafe:
     if optThreads in g.config.globalOptions and optThreadAnalysis in g.config.globalOptions:
diff --git a/compiler/varpartitions.nim b/compiler/varpartitions.nim
index 9297c19e16..474a362cd6 100644
--- a/compiler/varpartitions.nim
+++ b/compiler/varpartitions.nim
@@ -110,6 +110,9 @@ proc registerVariable(c: var Partitions; n: PNode) =
                             connectedVia: unknownLineInfo, flags: {connectsConstParam},
                             maxMutation: -1, minConnection: high(int),
                             mutations: @[])
+    elif n.sym.kind == skResult:
+      c.s.add VarIndex(kind: isEmptyRoot, sym: n.sym,
+                       aliveStart: high(int), aliveEnd: c.abstractTime)
     else:
       c.s.add VarIndex(kind: isEmptyRoot, sym: n.sym,
                        aliveStart: c.abstractTime, aliveEnd: c.abstractTime)
@@ -567,6 +570,8 @@ proc computeLiveRanges(c: var Partitions; n: PNode) =
       let id = variableId(c, n.sym)
       if id >= 0:
         c.s[id].aliveEnd = max(c.s[id].aliveEnd, c.abstractTime)
+        if n.sym.kind == skResult:
+          c.s[id].aliveStart = min(c.s[id].aliveStart, c.abstractTime)
 
   of nodesToIgnoreSet:
     dec c.abstractTime
@@ -621,7 +626,7 @@ proc computeGraphPartitions*(s: PSym; n: PNode; cursorInference = false): Partit
   traverse(result, n)
 
 proc dangerousMutation(g: MutationInfo; v: VarIndex): bool =
-  #echo "range ", v.aliveStart, " .. ", v.aliveEnd
+  #echo "range ", v.aliveStart, " .. ", v.aliveEnd, " ", v.sym
   if isMutated in g.flags:
     for m in g.mutations:
       #echo "mutation ", m
@@ -643,7 +648,7 @@ proc cannotBorrow(config: ConfigRef; s: PSym; g: MutationInfo) =
     m.add " is the statement that connected the mutation to the parameter"
   localError(config, s.info, m)
 
-proc checkBorrowedLocations*(par: var Partitions; config: ConfigRef) =
+proc checkBorrowedLocations*(par: var Partitions; body: PNode; config: ConfigRef) =
   for i in 0 ..< par.s.len:
     let s = par.s[i].sym
     if s.kind != skParam and isViewType(s.typ):