diff --git a/src/cmd/compile/internal/gc/plive.go b/src/cmd/compile/internal/gc/plive.go
index 7e1c0c1..bdb4580 100644
--- a/src/cmd/compile/internal/gc/plive.go
+++ b/src/cmd/compile/internal/gc/plive.go
@@ -140,24 +140,14 @@
 	regMaps     []liveRegMask
 
 	cache progeffectscache
-
-	// These are only populated if open-coded defers are being used.
-	// List of vars/stack slots storing defer args
-	openDeferVars []openDeferVarInfo
-	// Map from defer arg OpVarDef to the block where the OpVarDef occurs.
-	openDeferVardefToBlockMap map[*Node]*ssa.Block
-	// Map of blocks that cannot reach a return or exit (panic)
-	nonReturnBlocks map[*ssa.Block]bool
-}
-
-type openDeferVarInfo struct {
-	n         *Node // Var/stack slot storing a defer arg
-	varsIndex int   // Index of variable in lv.vars
 }
 
 // LivenessMap maps from *ssa.Value to LivenessIndex.
 type LivenessMap struct {
 	vals map[ssa.ID]LivenessIndex
+	// The set of live, pointer-containing variables at the deferreturn
+	// call (only set when open-coded defers are used).
+	deferreturn LivenessIndex
 }
 
 func (m *LivenessMap) reset() {
@@ -168,6 +158,7 @@
 			delete(m.vals, k)
 		}
 	}
+	m.deferreturn = LivenessInvalid
 }
 
 func (m *LivenessMap) set(v *ssa.Value, i LivenessIndex) {
@@ -542,7 +533,7 @@
 		if cap(lc.be) >= f.NumBlocks() {
 			lv.be = lc.be[:f.NumBlocks()]
 		}
-		lv.livenessMap = LivenessMap{lc.livenessMap.vals}
+		lv.livenessMap = LivenessMap{vals: lc.livenessMap.vals, deferreturn: LivenessInvalid}
 		lc.livenessMap.vals = nil
 	}
 	if lv.be == nil {
@@ -893,58 +884,12 @@
 func (lv *Liveness) prologue() {
 	lv.initcache()
 
-	if lv.fn.Func.HasDefer() && !lv.fn.Func.OpenCodedDeferDisallowed() {
-		lv.openDeferVardefToBlockMap = make(map[*Node]*ssa.Block)
-		for i, n := range lv.vars {
-			if n.Name.OpenDeferSlot() {
-				lv.openDeferVars = append(lv.openDeferVars, openDeferVarInfo{n: n, varsIndex: i})
-			}
-		}
-
-		// Find any blocks that cannot reach a return or a BlockExit
-		// (panic) -- these must be because of an infinite loop.
-		reachesRet := make(map[ssa.ID]bool)
-		blockList := make([]*ssa.Block, 0, 256)
-
-		for _, b := range lv.f.Blocks {
-			if b.Kind == ssa.BlockRet || b.Kind == ssa.BlockRetJmp || b.Kind == ssa.BlockExit {
-				blockList = append(blockList, b)
-			}
-		}
-
-		for len(blockList) > 0 {
-			b := blockList[0]
-			blockList = blockList[1:]
-			if reachesRet[b.ID] {
-				continue
-			}
-			reachesRet[b.ID] = true
-			for _, e := range b.Preds {
-				blockList = append(blockList, e.Block())
-			}
-		}
-
-		lv.nonReturnBlocks = make(map[*ssa.Block]bool)
-		for _, b := range lv.f.Blocks {
-			if !reachesRet[b.ID] {
-				lv.nonReturnBlocks[b] = true
-				//fmt.Println("No reach ret", lv.f.Name, b.ID, b.Kind)
-			}
-		}
-	}
-
 	for _, b := range lv.f.Blocks {
 		be := lv.blockEffects(b)
 
 		// Walk the block instructions backward and update the block
 		// effects with the each prog effects.
 		for j := len(b.Values) - 1; j >= 0; j-- {
-			if b.Values[j].Op == ssa.OpVarDef {
-				n := b.Values[j].Aux.(*Node)
-				if n.Name.OpenDeferSlot() {
-					lv.openDeferVardefToBlockMap[n] = b
-				}
-			}
 			pos, e := lv.valueEffects(b.Values[j])
 			regUevar, regKill := lv.regEffects(b.Values[j])
 			if e&varkill != 0 {
@@ -961,20 +906,6 @@
 	}
 }
 
-// markDeferVarsLive marks each variable storing an open-coded defer arg as
-// specially live in block b if the variable definition dominates block b.
-func (lv *Liveness) markDeferVarsLive(b *ssa.Block, newliveout *varRegVec) {
-	// Only force computation of dominators if we have a block where we need
-	// to specially mark defer args live.
-	sdom := lv.f.Sdom()
-	for _, info := range lv.openDeferVars {
-		defB := lv.openDeferVardefToBlockMap[info.n]
-		if sdom.IsAncestorEq(defB, b) {
-			newliveout.vars.Set(int32(info.varsIndex))
-		}
-	}
-}
-
 // Solve the liveness dataflow equations.
 func (lv *Liveness) solve() {
 	// These temporary bitvectors exist to avoid successive allocations and
@@ -1018,23 +949,6 @@
 				}
 			}
 
-			if lv.fn.Func.HasDefer() && !lv.fn.Func.OpenCodedDeferDisallowed() &&
-				(b.Kind == ssa.BlockExit || lv.nonReturnBlocks[b]) {
-				// Open-coded defer args slots must be live
-				// everywhere in a function, since a panic can
-				// occur (almost) anywhere. Force all appropriate
-				// defer arg slots to be live in BlockExit (panic)
-				// blocks and in blocks that do not reach a return
-				// (because of infinite loop).
-				//
-				// We are assuming that the defer exit code at
-				// BlockReturn/BlockReturnJmp accesses all of the
-				// defer args (with pointers), and so keeps them
-				// live. This analysis may have to be adjusted if
-				// that changes (because of optimizations).
-				lv.markDeferVarsLive(b, &newliveout)
-			}
-
 			if !be.liveout.Eq(newliveout) {
 				change = true
 				be.liveout.Copy(newliveout)
@@ -1087,6 +1001,17 @@
 				n.Name.SetNeedzero(true)
 				livedefer.Set(int32(i))
 			}
+			if n.Name.OpenDeferSlot() {
+				// Open-coded defer args slots must be live
+				// everywhere in a function, since a panic can
+				// occur (almost) anywhere. Because it is live
+				// everywhere, it must be zeroed on entry.
+				livedefer.Set(int32(i))
+				// It was already marked as Needzero when created.
+				if !n.Name.Needzero() {
+					Fatalf("all pointer-containing defer arg slots should have Needzero set")
+				}
+			}
 		}
 	}
 
@@ -1188,6 +1113,17 @@
 		lv.compact(b)
 	}
 
+	// If we have an open-coded deferreturn call, make a liveness map for it.
+	if lv.fn.Func.OpenCodedDeferDisallowed() {
+		lv.livenessMap.deferreturn = LivenessInvalid
+	} else {
+		lv.livenessMap.deferreturn = LivenessIndex{
+			stackMapIndex: lv.stackMapSet.add(livedefer),
+			regMapIndex:   0, // entry regMap, containing no live registers
+			isUnsafePoint: false,
+		}
+	}
+
 	// Done compacting. Throw out the stack map set.
 	lv.stackMaps = lv.stackMapSet.extractUniqe()
 	lv.stackMapSet = bvecSet{}
diff --git a/src/cmd/compile/internal/gc/ssa.go b/src/cmd/compile/internal/gc/ssa.go
index d4d23a2..5d0098b 100644
--- a/src/cmd/compile/internal/gc/ssa.go
+++ b/src/cmd/compile/internal/gc/ssa.go
@@ -4318,12 +4318,6 @@
 			}
 		}
 
-		if i == len(s.openDefers)-1 {
-			// Record the call of the first defer. This will be used
-			// to set liveness info for the deferreturn (which is also
-			// used for any location that causes a runtime panic)
-			s.f.LastDeferExit = call
-		}
 		s.endBlock()
 		s.startBlock(bEnd)
 	}
@@ -5807,11 +5801,6 @@
 
 	// wasm: The number of values on the WebAssembly stack. This is only used as a safeguard.
 	OnWasmStackSkipped int
-
-	// Liveness index for the first function call in the final defer exit code
-	// path that we generated. All defer functions and args should be live at
-	// this point. This will be used to set the liveness for the deferreturn.
-	lastDeferLiveness LivenessIndex
 }
 
 // Prog appends a new Prog.
@@ -6056,12 +6045,6 @@
 				// instruction.
 				s.pp.nextLive = s.livenessMap.Get(v)
 
-				// Remember the liveness index of the first defer call of
-				// the last defer exit
-				if v.Block.Func.LastDeferExit != nil && v == v.Block.Func.LastDeferExit {
-					s.lastDeferLiveness = s.pp.nextLive
-				}
-
 				// Special case for first line in function; move it to the start.
 				if firstPos != src.NoXPos {
 					s.SetPos(firstPos)
@@ -6122,7 +6105,7 @@
 		// When doing open-coded defers, generate a disconnected call to
 		// deferreturn and a return. This will be used to during panic
 		// recovery to unwind the stack and return back to the runtime.
-		s.pp.nextLive = s.lastDeferLiveness
+		s.pp.nextLive = s.livenessMap.deferreturn
 		gencallret(pp, Deferreturn)
 	}
 
diff --git a/src/cmd/compile/internal/ssa/func.go b/src/cmd/compile/internal/ssa/func.go
index 7cf72a8..4b9189f 100644
--- a/src/cmd/compile/internal/ssa/func.go
+++ b/src/cmd/compile/internal/ssa/func.go
@@ -33,15 +33,8 @@
 	Blocks []*Block    // unordered set of all basic blocks (note: not indexable by ID)
 	Entry  *Block      // the entry basic block
 
-	// If we are using open-coded defers, this is the first call to a deferred
-	// function in the final defer exit sequence that we generated. This call
-	// should be after all defer statements, and will have all args, etc. of
-	// all defer calls as live. The liveness info of this call will be used
-	// for the deferreturn/ret segment generated for functions with open-coded
-	// defers.
-	LastDeferExit *Value
-	bid           idAlloc // block ID allocator
-	vid           idAlloc // value ID allocator
+	bid idAlloc // block ID allocator
+	vid idAlloc // value ID allocator
 
 	// Given an environment variable used for debug hash match,
 	// what file (if any) receives the yes/no logging?
diff --git a/test/fixedbugs/issue40629.go b/test/fixedbugs/issue40629.go
new file mode 100644
index 0000000..c6ef408
--- /dev/null
+++ b/test/fixedbugs/issue40629.go
@@ -0,0 +1,69 @@
+// run
+
+// Copyright 2020 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package main
+
+import "fmt"
+
+const N = 40
+
+func main() {
+	var x [N]int // stack-allocated memory
+	for i := range x {
+		x[i] = 0x999
+	}
+
+	// This defer checks to see if x is uncorrupted.
+	defer func(p *[N]int) {
+		recover()
+		for i := range p {
+			if p[i] != 0x999 {
+				for j := range p {
+					fmt.Printf("p[%d]=0x%x\n", j, p[j])
+				}
+				panic("corrupted stack variable")
+			}
+		}
+	}(&x)
+
+	// This defer starts a new goroutine, which will (hopefully)
+	// overwrite x on the garbage stack.
+	defer func() {
+		c := make(chan bool)
+		go func() {
+			useStack(1000)
+			c <- true
+		}()
+		<-c
+
+	}()
+
+	// This defer causes a stack copy.
+	// The old stack is now garbage.
+	defer func() {
+		useStack(1000)
+	}()
+
+	// Trigger a segfault.
+	*g = 0
+
+	// Make the return statement unreachable.
+	// That makes the stack map at the deferreturn call empty.
+	// In particular, the argument to the first defer is not
+	// marked as a pointer, so it doesn't get adjusted
+	// during the stack copy.
+	for {
+	}
+}
+
+var g *int64
+
+func useStack(n int) {
+	if n == 0 {
+		return
+	}
+	useStack(n - 1)
+}