Reboot of #16195 (#16746)

* fix #16185

* fix test

* fix comment

* fix comment

* better approach

* Add more tests and move sameLocation to injectdestructors

* Better and more strict sameLocation

* Small cleanup and preliminary spec clarification

* Fix

* Fix doc

* Expand test

Co-authored-by: Andrey R (cooldome) <ariabushenko@gmail.com>

1 files changed, 85 insertions, 58 deletions

diff --git a/compiler/injectdestructors.nim b/compiler/injectdestructors.nim
index 76a063faa..48c501209 100644
--- a/compiler/injectdestructors.nim
+++ b/compiler/injectdestructors.nim
@@ -968,68 +968,95 @@ proc p(n: PNode; c: var Con; s: var Scope; mode: ProcessMode): PNode =
     else:
       internalError(c.graph.config, n.info, "cannot inject destructors to node kind: " & $n.kind)
 
+proc sameLocation*(a, b: PNode): bool =
+  proc sameConstant(a, b: PNode): bool =
+    a.kind in nkLiterals and exprStructuralEquivalent(a, b)
+
+  const nkEndPoint = {nkSym, nkDotExpr, nkCheckedFieldExpr, nkBracketExpr}
+  if a.kind in nkEndPoint and b.kind in nkEndPoint:
+    if a.kind == b.kind:
+      case a.kind
+      of nkSym: a.sym == b.sym
+      of nkDotExpr, nkCheckedFieldExpr: sameLocation(a[0], b[0]) and sameLocation(a[1], b[1])
+      of nkBracketExpr: sameLocation(a[0], b[0]) and sameConstant(a[1], b[1])
+      else: false
+    else: false
+  else:
+    case a.kind
+    of nkSym, nkDotExpr, nkCheckedFieldExpr, nkBracketExpr:
+      # Reached an endpoint, flip to recurse the other side.
+      sameLocation(b, a)
+    of nkAddr, nkHiddenAddr, nkDerefExpr, nkHiddenDeref:
+      # We don't need to check addr/deref levels or differentiate between the two,
+      # since pointers don't have hooks :) (e.g: var p: ptr pointer; p[] = addr p)
+      sameLocation(a[0], b)
+    of nkObjDownConv, nkObjUpConv: sameLocation(a[0], b)
+    of nkHiddenStdConv, nkHiddenSubConv: sameLocation(a[1], b)
+    else: false
+
 proc moveOrCopy(dest, ri: PNode; c: var Con; s: var Scope, isDecl = false): PNode =
-  case ri.kind
-  of nkCallKinds:
-    result = c.genSink(dest, p(ri, c, s, consumed), isDecl)
-  of nkBracketExpr:
-    if isUnpackedTuple(ri[0]):
-      # unpacking of tuple: take over the elements
+  if sameLocation(dest, ri):
+    # rule (self-assignment-removal):
+    result = newNodeI(nkEmpty, dest.info)
+  else:
+    case ri.kind
+    of nkCallKinds:
       result = c.genSink(dest, p(ri, c, s, consumed), isDecl)
-    elif isAnalysableFieldAccess(ri, c.owner) and isLastRead(ri, c) and
-        not aliases(dest, ri):
-      # Rule 3: `=sink`(x, z); wasMoved(z)
-      var snk = c.genSink(dest, ri, isDecl)
-      result = newTree(nkStmtList, snk, c.genWasMoved(ri))
-    else:
-      result = c.genCopy(dest, ri)
-      result.add p(ri, c, s, consumed)
-      c.finishCopy(result, dest, isFromSink = false)
-  of nkBracket:
-    # array constructor
-    if ri.len > 0 and isDangerousSeq(ri.typ):
-      result = c.genCopy(dest, ri)
-      result.add p(ri, c, s, consumed)
-      c.finishCopy(result, dest, isFromSink = false)
-    else:
+    of nkBracketExpr:
+      if isUnpackedTuple(ri[0]):
+        # unpacking of tuple: take over the elements
+        result = c.genSink(dest, p(ri, c, s, consumed), isDecl)
+      elif isAnalysableFieldAccess(ri, c.owner) and isLastRead(ri, c) and
+          not aliases(dest, ri):
+        # Rule 3: `=sink`(x, z); wasMoved(z)
+        var snk = c.genSink(dest, ri, isDecl)
+        result = newTree(nkStmtList, snk, c.genWasMoved(ri))
+      else:
+        result = c.genCopy(dest, ri)
+        result.add p(ri, c, s, consumed)
+        c.finishCopy(result, dest, isFromSink = false)
+    of nkBracket:
+      # array constructor
+      if ri.len > 0 and isDangerousSeq(ri.typ):
+        result = c.genCopy(dest, ri)
+        result.add p(ri, c, s, consumed)
+        c.finishCopy(result, dest, isFromSink = false)
+      else:
+        result = c.genSink(dest, p(ri, c, s, consumed), isDecl)
+    of nkObjConstr, nkTupleConstr, nkClosure, nkCharLit..nkNilLit:
       result = c.genSink(dest, p(ri, c, s, consumed), isDecl)
-  of nkObjConstr, nkTupleConstr, nkClosure, nkCharLit..nkNilLit:
-    result = c.genSink(dest, p(ri, c, s, consumed), isDecl)
-  of nkSym:
-    if dest.kind == nkSym and dest.sym == ri.sym:
-      # rule (self-assignment-removal):
-      result = newNodeI(nkEmpty, dest.info)
-    elif isSinkParam(ri.sym) and isLastRead(ri, c):
-      # Rule 3: `=sink`(x, z); wasMoved(z)
-      let snk = c.genSink(dest, ri, isDecl)
-      result = newTree(nkStmtList, snk, c.genWasMoved(ri))
-    elif ri.sym.kind != skParam and ri.sym.owner == c.owner and
-        isLastRead(ri, c) and canBeMoved(c, dest.typ) and not isCursor(ri, c):
-      # Rule 3: `=sink`(x, z); wasMoved(z)
-      let snk = c.genSink(dest, ri, isDecl)
-      result = newTree(nkStmtList, snk, c.genWasMoved(ri))
-    else:
-      result = c.genCopy(dest, ri)
-      result.add p(ri, c, s, consumed)
-      c.finishCopy(result, dest, isFromSink = false)
-  of nkHiddenSubConv, nkHiddenStdConv, nkConv, nkObjDownConv, nkObjUpConv:
-    result = c.genSink(dest, p(ri, c, s, sinkArg), isDecl)
-  of nkStmtListExpr, nkBlockExpr, nkIfExpr, nkCaseStmt, nkTryStmt:
-    template process(child, s): untyped = moveOrCopy(dest, child, c, s, isDecl)
-    # We know the result will be a stmt so we use that fact to optimize
-    handleNestedTempl(ri, process, willProduceStmt = true)
-  of nkRaiseStmt:
-    result = pRaiseStmt(ri, c, s)
-  else:
-    if isAnalysableFieldAccess(ri, c.owner) and isLastRead(ri, c) and
-        canBeMoved(c, dest.typ):
-      # Rule 3: `=sink`(x, z); wasMoved(z)
-      let snk = c.genSink(dest, ri, isDecl)
-      result = newTree(nkStmtList, snk, c.genWasMoved(ri))
+    of nkSym:
+      if isSinkParam(ri.sym) and isLastRead(ri, c):
+        # Rule 3: `=sink`(x, z); wasMoved(z)
+        let snk = c.genSink(dest, ri, isDecl)
+        result = newTree(nkStmtList, snk, c.genWasMoved(ri))
+      elif ri.sym.kind != skParam and ri.sym.owner == c.owner and
+          isLastRead(ri, c) and canBeMoved(c, dest.typ) and not isCursor(ri, c):
+        # Rule 3: `=sink`(x, z); wasMoved(z)
+        let snk = c.genSink(dest, ri, isDecl)
+        result = newTree(nkStmtList, snk, c.genWasMoved(ri))
+      else:
+        result = c.genCopy(dest, ri)
+        result.add p(ri, c, s, consumed)
+        c.finishCopy(result, dest, isFromSink = false)
+    of nkHiddenSubConv, nkHiddenStdConv, nkConv, nkObjDownConv, nkObjUpConv:
+      result = c.genSink(dest, p(ri, c, s, sinkArg), isDecl)
+    of nkStmtListExpr, nkBlockExpr, nkIfExpr, nkCaseStmt, nkTryStmt:
+      template process(child, s): untyped = moveOrCopy(dest, child, c, s, isDecl)
+      # We know the result will be a stmt so we use that fact to optimize
+      handleNestedTempl(ri, process, willProduceStmt = true)
+    of nkRaiseStmt:
+      result = pRaiseStmt(ri, c, s)
     else:
-      result = c.genCopy(dest, ri)
-      result.add p(ri, c, s, consumed)
-      c.finishCopy(result, dest, isFromSink = false)
+      if isAnalysableFieldAccess(ri, c.owner) and isLastRead(ri, c) and
+          canBeMoved(c, dest.typ):
+        # Rule 3: `=sink`(x, z); wasMoved(z)
+        let snk = c.genSink(dest, ri, isDecl)
+        result = newTree(nkStmtList, snk, c.genWasMoved(ri))
+      else:
+        result = c.genCopy(dest, ri)
+        result.add p(ri, c, s, consumed)
+        c.finishCopy(result, dest, isFromSink = false)
 
 proc computeUninit(c: var Con) =
   if not c.uninitComputed: