diff --git a/src/cmd/compile/internal/ssa/gen/generic.rules b/src/cmd/compile/internal/ssa/gen/generic.rules
index 87cfd3d..89368ed 100644
--- a/src/cmd/compile/internal/ssa/gen/generic.rules
+++ b/src/cmd/compile/internal/ssa/gen/generic.rules
@@ -2351,7 +2351,7 @@
 (Move {t1} [s] dst tmp1 midmem:(Move {t2} [s] tmp2 src _))
 	&& t1.(*types.Type).Compare(t2.(*types.Type)) == types.CMPeq
 	&& isSamePtr(tmp1, tmp2)
-	&& isStackPtr(src)
+	&& isStackPtr(src) && !isVolatile(src)
 	&& disjoint(src, s, tmp2, s)
 	&& (disjoint(src, s, dst, s) || isInlinableMemmove(dst, src, s, config))
 	-> (Move {t1} [s] dst src midmem)
@@ -2360,7 +2360,7 @@
 (Move {t1} [s] dst tmp1 midmem:(VarDef (Move {t2} [s] tmp2 src _)))
 	&& t1.(*types.Type).Compare(t2.(*types.Type)) == types.CMPeq
 	&& isSamePtr(tmp1, tmp2)
-	&& isStackPtr(src)
+	&& isStackPtr(src) && !isVolatile(src)
 	&& disjoint(src, s, tmp2, s)
 	&& (disjoint(src, s, dst, s) || isInlinableMemmove(dst, src, s, config))
 	-> (Move {t1} [s] dst src midmem)
diff --git a/src/cmd/compile/internal/ssa/rewritegeneric.go b/src/cmd/compile/internal/ssa/rewritegeneric.go
index d65d900..72abaf2 100644
--- a/src/cmd/compile/internal/ssa/rewritegeneric.go
+++ b/src/cmd/compile/internal/ssa/rewritegeneric.go
@@ -32031,7 +32031,7 @@
 		return true
 	}
 	// match: (Move {t1} [s] dst tmp1 midmem:(Move {t2} [s] tmp2 src _))
-	// cond: t1.(*types.Type).Compare(t2.(*types.Type)) == types.CMPeq && isSamePtr(tmp1, tmp2) && isStackPtr(src) && disjoint(src, s, tmp2, s) && (disjoint(src, s, dst, s) || isInlinableMemmove(dst, src, s, config))
+	// cond: t1.(*types.Type).Compare(t2.(*types.Type)) == types.CMPeq && isSamePtr(tmp1, tmp2) && isStackPtr(src) && !isVolatile(src) && disjoint(src, s, tmp2, s) && (disjoint(src, s, dst, s) || isInlinableMemmove(dst, src, s, config))
 	// result: (Move {t1} [s] dst src midmem)
 	for {
 		s := v.AuxInt
@@ -32047,7 +32047,7 @@
 		_ = midmem.Args[2]
 		tmp2 := midmem.Args[0]
 		src := midmem.Args[1]
-		if !(t1.(*types.Type).Compare(t2.(*types.Type)) == types.CMPeq && isSamePtr(tmp1, tmp2) && isStackPtr(src) && disjoint(src, s, tmp2, s) && (disjoint(src, s, dst, s) || isInlinableMemmove(dst, src, s, config))) {
+		if !(t1.(*types.Type).Compare(t2.(*types.Type)) == types.CMPeq && isSamePtr(tmp1, tmp2) && isStackPtr(src) && !isVolatile(src) && disjoint(src, s, tmp2, s) && (disjoint(src, s, dst, s) || isInlinableMemmove(dst, src, s, config))) {
 			break
 		}
 		v.reset(OpMove)
@@ -32059,7 +32059,7 @@
 		return true
 	}
 	// match: (Move {t1} [s] dst tmp1 midmem:(VarDef (Move {t2} [s] tmp2 src _)))
-	// cond: t1.(*types.Type).Compare(t2.(*types.Type)) == types.CMPeq && isSamePtr(tmp1, tmp2) && isStackPtr(src) && disjoint(src, s, tmp2, s) && (disjoint(src, s, dst, s) || isInlinableMemmove(dst, src, s, config))
+	// cond: t1.(*types.Type).Compare(t2.(*types.Type)) == types.CMPeq && isSamePtr(tmp1, tmp2) && isStackPtr(src) && !isVolatile(src) && disjoint(src, s, tmp2, s) && (disjoint(src, s, dst, s) || isInlinableMemmove(dst, src, s, config))
 	// result: (Move {t1} [s] dst src midmem)
 	for {
 		s := v.AuxInt
@@ -32079,7 +32079,7 @@
 		_ = midmem_0.Args[2]
 		tmp2 := midmem_0.Args[0]
 		src := midmem_0.Args[1]
-		if !(t1.(*types.Type).Compare(t2.(*types.Type)) == types.CMPeq && isSamePtr(tmp1, tmp2) && isStackPtr(src) && disjoint(src, s, tmp2, s) && (disjoint(src, s, dst, s) || isInlinableMemmove(dst, src, s, config))) {
+		if !(t1.(*types.Type).Compare(t2.(*types.Type)) == types.CMPeq && isSamePtr(tmp1, tmp2) && isStackPtr(src) && !isVolatile(src) && disjoint(src, s, tmp2, s) && (disjoint(src, s, dst, s) || isInlinableMemmove(dst, src, s, config))) {
 			break
 		}
 		v.reset(OpMove)
diff --git a/src/cmd/go/internal/work/action.go b/src/cmd/go/internal/work/action.go
index 8256681..e3cb87f 100644
--- a/src/cmd/go/internal/work/action.go
+++ b/src/cmd/go/internal/work/action.go
@@ -56,9 +56,6 @@
 	id           sync.Mutex
 	toolIDCache  map[string]string // tool name -> tool ID
 	buildIDCache map[string]string // file name -> build ID
-
-	cgoEnvOnce  sync.Once
-	cgoEnvCache []string
 }
 
 // NOTE: Much of Action would not need to be exported if not for test.
diff --git a/src/cmd/go/internal/work/exec.go b/src/cmd/go/internal/work/exec.go
index 8230d85..1c50f47 100644
--- a/src/cmd/go/internal/work/exec.go
+++ b/src/cmd/go/internal/work/exec.go
@@ -1076,7 +1076,10 @@
 	}
 
 	// TODO(rsc): Why do we pass $GCCGO to go vet?
-	env := b.cgoEnv()
+	env := b.cCompilerEnv()
+	if cfg.BuildToolchainName == "gccgo" {
+		env = append(env, "GCCGO="+BuildToolchain.compiler())
+	}
 
 	p := a.Package
 	tool := VetTool
@@ -1980,24 +1983,6 @@
 	return []string{"TERM=dumb"}
 }
 
-// cgoEnv returns environment variables to set when running cgo.
-// Some of these pass through to cgo running the C compiler,
-// so it includes cCompilerEnv.
-func (b *Builder) cgoEnv() []string {
-	b.cgoEnvOnce.Do(func() {
-		cc, err := exec.LookPath(b.ccExe()[0])
-		if err != nil || filepath.Base(cc) == cc { // reject relative path
-			cc = "/missing-cc"
-		}
-		gccgo := GccgoBin
-		if filepath.Base(gccgo) == gccgo { // reject relative path
-			gccgo = "/missing-gccgo"
-		}
-		b.cgoEnvCache = append(b.cCompilerEnv(), "CC="+cc, "GCCGO="+gccgo)
-	})
-	return b.cgoEnvCache
-}
-
 // mkdir makes the named directory.
 func (b *Builder) Mkdir(dir string) error {
 	// Make Mkdir(a.Objdir) a no-op instead of an error when a.Objdir == "".
@@ -2543,7 +2528,7 @@
 	// along to the host linker. At this point in the code, cgoLDFLAGS
 	// consists of the original $CGO_LDFLAGS (unchecked) and all the
 	// flags put together from source code (checked).
-	cgoenv := b.cgoEnv()
+	cgoenv := b.cCompilerEnv()
 	if len(cgoLDFLAGS) > 0 {
 		flags := make([]string, len(cgoLDFLAGS))
 		for i, f := range cgoLDFLAGS {
@@ -2764,7 +2749,7 @@
 	if p.Standard && p.ImportPath == "runtime/cgo" {
 		cgoflags = []string{"-dynlinker"} // record path to dynamic linker
 	}
-	return b.run(a, p.Dir, p.ImportPath, b.cgoEnv(), cfg.BuildToolexec, cgoExe, "-dynpackage", p.Name, "-dynimport", dynobj, "-dynout", importGo, cgoflags)
+	return b.run(a, p.Dir, p.ImportPath, b.cCompilerEnv(), cfg.BuildToolexec, cgoExe, "-dynpackage", p.Name, "-dynimport", dynobj, "-dynout", importGo, cgoflags)
 }
 
 // Run SWIG on all SWIG input files.
diff --git a/src/cmd/go/testdata/script/cgo_path.txt b/src/cmd/go/testdata/script/cgo_path.txt
index e4d07de..548a65f 100644
--- a/src/cmd/go/testdata/script/cgo_path.txt
+++ b/src/cmd/go/testdata/script/cgo_path.txt
@@ -1,12 +1,20 @@
 [!cgo] skip
 
+# Set CC explicitly to something that requires a PATH lookup.
+# Normally, the default is gcc or clang, but if CC was set during make.bash,
+# that becomes the default.
+[exec:clang] env CC=clang
+[exec:gcc] env CC=gcc
+[!exec:clang] [!exec:gcc] skip 'Unknown C compiler'
+
 env GOCACHE=$WORK/gocache  # Looking for compile flags, so need a clean cache.
 [!windows] env PATH=.:$PATH
-[!windows] chmod 0777 p/gcc p/clang
+[!windows] chmod 0755 p/gcc p/clang
 [!windows] exists p/gcc p/clang
 [windows] exists p/gcc.bat p/clang.bat
 ! exists p/bug.txt
-go build -x
+! go build -x
+stderr '^cgo: exec (clang|gcc): (clang|gcc) resolves to executable in current directory \(.[/\\](clang|gcc)(.bat)?\)$'
 ! exists p/bug.txt
 
 -- go.mod --
diff --git a/src/cmd/go/testdata/script/cgo_path_space.txt b/src/cmd/go/testdata/script/cgo_path_space.txt
new file mode 100644
index 0000000..3ae8dce
--- /dev/null
+++ b/src/cmd/go/testdata/script/cgo_path_space.txt
@@ -0,0 +1,52 @@
+# Check that if the PATH directory containing the C compiler has a space,
+# we can still use that compiler with cgo.
+# Verifies #43808.
+[!cgo] skip
+
+# Set CC explicitly to something that requires a PATH lookup.
+# Normally, the default is gcc or clang, but if CC was set during make.bash,
+# that becomes the default.
+[exec:clang] env CC=clang
+[exec:gcc] env CC=gcc
+[!exec:clang] [!exec:gcc] skip 'Unknown C compiler'
+
+[!windows] chmod 0755 $WORK/'program files'/clang
+[!windows] chmod 0755 $WORK/'program files'/gcc
+[!windows] env PATH=$WORK/'program files':$PATH
+[windows] env PATH=$WORK\'program files';%PATH%
+
+! exists $WORK/log.txt
+! go build -x
+exists $WORK/log.txt
+rm $WORK/log.txt
+
+# TODO(#41400, #43078): when CC is set explicitly, it should be allowed to
+# contain spaces separating arguments, and it should be possible to quote
+# arguments with spaces (including the path), as in CGO_CFLAGS and other
+# variables. For now, this doesn't work.
+[!windows] env CC=$WORK/'program files'/gcc
+[windows] env CC=$WORK\'program files'\gcc.bat
+! go build -x
+! exists $WORK/log.txt
+
+-- go.mod --
+module m
+
+-- m.go --
+package m
+
+// #define X 1
+import "C"
+
+-- $WORK/program files/gcc --
+#!/bin/sh
+
+echo ok >$WORK/log.txt
+-- $WORK/program files/clang --
+#!/bin/sh
+
+echo ok >$WORK/log.txt
+-- $WORK/program files/gcc.bat --
+echo ok >%WORK%\log.txt
+-- $WORK/program files/clang.bat --
+echo ok >%WORK%\log.txt
diff --git a/src/cmd/go/testdata/script/mod_get_fallback.txt b/src/cmd/go/testdata/script/mod_get_fallback.txt
index a9834a3..9733fa3 100644
--- a/src/cmd/go/testdata/script/mod_get_fallback.txt
+++ b/src/cmd/go/testdata/script/mod_get_fallback.txt
@@ -6,5 +6,5 @@
 env GOSUMDB=off
 
 go get -x -v -d golang.org/x/tools/cmd/goimports
-stderr '# get https://proxy.golang.org/golang.org/x/tools/@latest'
+stderr '# get https://proxy.golang.org/golang.org/x/tools/@v/list'
 ! stderr '# get https://golang.org'
diff --git a/src/go.mod b/src/go.mod
index faf848d..ec6bd98 100644
--- a/src/go.mod
+++ b/src/go.mod
@@ -4,7 +4,7 @@
 
 require (
 	golang.org/x/crypto v0.0.0-20200128174031-69ecbb4d6d5d
-	golang.org/x/net v0.0.0-20201029202311-70d85028bad3
+	golang.org/x/net v0.0.0-20210129194117-4acb7895a057
 	golang.org/x/sys v0.0.0-20200201011859-915c9c3d4ccf // indirect
 	golang.org/x/text v0.3.3-0.20191031172631-4b67af870c6f // indirect
 )
diff --git a/src/go.sum b/src/go.sum
index 58d6621..171e083 100644
--- a/src/go.sum
+++ b/src/go.sum
@@ -2,8 +2,8 @@
 golang.org/x/crypto v0.0.0-20200128174031-69ecbb4d6d5d h1:9FCpayM9Egr1baVnV1SX0H87m+XB0B8S0hAMi99X/3U=
 golang.org/x/crypto v0.0.0-20200128174031-69ecbb4d6d5d/go.mod h1:LzIPMQfyMNhhGPhUkYOs5KpL4U8rLKemX1yGLhDgUto=
 golang.org/x/net v0.0.0-20190404232315-eb5bcb51f2a3/go.mod h1:t9HGtf8HONx5eT2rtn7q6eTqICYqUVnKs3thJo3Qplg=
-golang.org/x/net v0.0.0-20201029202311-70d85028bad3 h1:zhmuDiUI8/S25xjIBeUn8XwfxP7SKYR41pTuOoa1O+w=
-golang.org/x/net v0.0.0-20201029202311-70d85028bad3/go.mod h1:z5CRVTTTmAJ677TzLLGU+0bjPO0LkuOLi4/5GtJWs/s=
+golang.org/x/net v0.0.0-20210129194117-4acb7895a057 h1:HThQeV5c0Ab/Puir+q6mC97b7+3dfZdsLWMLoBrzo68=
+golang.org/x/net v0.0.0-20210129194117-4acb7895a057/go.mod h1:z5CRVTTTmAJ677TzLLGU+0bjPO0LkuOLi4/5GtJWs/s=
 golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/sys v0.0.0-20190412213103-97732733099d/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20200201011859-915c9c3d4ccf h1:+4j7oujXP478CVb/AFvHJmVX5+Pczx2NGts5yirA0oY=
diff --git a/src/internal/execabs/execabs_test.go b/src/internal/execabs/execabs_test.go
index a0b88dd..1a197b8 100644
--- a/src/internal/execabs/execabs_test.go
+++ b/src/internal/execabs/execabs_test.go
@@ -7,6 +7,7 @@
 import (
 	"context"
 	"fmt"
+	"internal/testenv"
 	"io/ioutil"
 	"os"
 	"os/exec"
@@ -30,6 +31,8 @@
 }
 
 func TestCommand(t *testing.T) {
+	testenv.MustHaveExec(t)
+
 	for _, cmd := range []func(string) *Cmd{
 		func(s string) *Cmd { return Command(s) },
 		func(s string) *Cmd { return CommandContext(context.Background(), s) },
@@ -71,6 +74,8 @@
 }
 
 func TestLookPath(t *testing.T) {
+	testenv.MustHaveExec(t)
+
 	tmpDir, err := ioutil.TempDir("", "execabs-test")
 	if err != nil {
 		t.Fatalf("ioutil.TempDir failed: %s", err)
diff --git a/src/net/http/h2_bundle.go b/src/net/http/h2_bundle.go
index 0e9139b..8f39241 100644
--- a/src/net/http/h2_bundle.go
+++ b/src/net/http/h2_bundle.go
@@ -7593,6 +7593,9 @@
 			// we can keep it.
 			bodyWriter.cancel()
 			cs.abortRequestBodyWrite(http2errStopReqBodyWrite)
+			if hasBody && !bodyWritten {
+				<-bodyWriter.resc
+			}
 		}
 		if re.err != nil {
 			cc.forgetStreamID(cs.ID)
@@ -7613,6 +7616,7 @@
 			} else {
 				bodyWriter.cancel()
 				cs.abortRequestBodyWrite(http2errStopReqBodyWriteAndCancel)
+				<-bodyWriter.resc
 			}
 			cc.forgetStreamID(cs.ID)
 			return nil, cs.getStartedWrite(), http2errTimeout
@@ -7622,6 +7626,7 @@
 			} else {
 				bodyWriter.cancel()
 				cs.abortRequestBodyWrite(http2errStopReqBodyWriteAndCancel)
+				<-bodyWriter.resc
 			}
 			cc.forgetStreamID(cs.ID)
 			return nil, cs.getStartedWrite(), ctx.Err()
@@ -7631,6 +7636,7 @@
 			} else {
 				bodyWriter.cancel()
 				cs.abortRequestBodyWrite(http2errStopReqBodyWriteAndCancel)
+				<-bodyWriter.resc
 			}
 			cc.forgetStreamID(cs.ID)
 			return nil, cs.getStartedWrite(), http2errRequestCanceled
@@ -7640,6 +7646,7 @@
 			// forgetStreamID.
 			return nil, cs.getStartedWrite(), cs.resetErr
 		case err := <-bodyWriter.resc:
+			bodyWritten = true
 			// Prefer the read loop's response, if available. Issue 16102.
 			select {
 			case re := <-readLoopResCh:
@@ -7650,7 +7657,6 @@
 				cc.forgetStreamID(cs.ID)
 				return nil, cs.getStartedWrite(), err
 			}
-			bodyWritten = true
 			if d := cc.responseHeaderTimeout(); d != 0 {
 				timer := time.NewTimer(d)
 				defer timer.Stop()
@@ -9055,7 +9061,9 @@
 
 func (s http2bodyWriterState) cancel() {
 	if s.timer != nil {
-		s.timer.Stop()
+		if s.timer.Stop() {
+			s.resc <- nil
+		}
 	}
 }
 
diff --git a/src/runtime/cgo/gcc_linux_386.c b/src/runtime/cgo/gcc_linux_386.c
index ece9f93..70c942a 100644
--- a/src/runtime/cgo/gcc_linux_386.c
+++ b/src/runtime/cgo/gcc_linux_386.c
@@ -12,7 +12,7 @@
 static void (*setg_gcc)(void*);
 
 // This will be set in gcc_android.c for android-specific customization.
-void (*x_cgo_inittls)(void **tlsg, void **tlsbase);
+void (*x_cgo_inittls)(void **tlsg, void **tlsbase) __attribute__((common));
 
 void
 x_cgo_init(G *g, void (*setg)(void*), void **tlsg, void **tlsbase)
diff --git a/src/runtime/cgo/gcc_linux_amd64.c b/src/runtime/cgo/gcc_linux_amd64.c
index 9134e0d..f2bf648 100644
--- a/src/runtime/cgo/gcc_linux_amd64.c
+++ b/src/runtime/cgo/gcc_linux_amd64.c
@@ -14,7 +14,7 @@
 static void (*setg_gcc)(void*);
 
 // This will be set in gcc_android.c for android-specific customization.
-void (*x_cgo_inittls)(void **tlsg, void **tlsbase);
+void (*x_cgo_inittls)(void **tlsg, void **tlsbase) __attribute__((common));
 
 void
 x_cgo_init(G *g, void (*setg)(void*), void **tlsg, void **tlsbase)
diff --git a/src/runtime/cgo/gcc_linux_arm.c b/src/runtime/cgo/gcc_linux_arm.c
index 61855b9..5bc0fee 100644
--- a/src/runtime/cgo/gcc_linux_arm.c
+++ b/src/runtime/cgo/gcc_linux_arm.c
@@ -10,7 +10,7 @@
 
 static void *threadentry(void*);
 
-void (*x_cgo_inittls)(void **tlsg, void **tlsbase);
+void (*x_cgo_inittls)(void **tlsg, void **tlsbase) __attribute__((common));
 static void (*setg_gcc)(void*);
 
 void
diff --git a/src/runtime/cgo/gcc_linux_arm64.c b/src/runtime/cgo/gcc_linux_arm64.c
index 261c884..17ff274 100644
--- a/src/runtime/cgo/gcc_linux_arm64.c
+++ b/src/runtime/cgo/gcc_linux_arm64.c
@@ -12,7 +12,7 @@
 
 static void *threadentry(void*);
 
-void (*x_cgo_inittls)(void **tlsg, void **tlsbase);
+void (*x_cgo_inittls)(void **tlsg, void **tlsbase) __attribute__((common));
 static void (*setg_gcc)(void*);
 
 void
diff --git a/src/vendor/modules.txt b/src/vendor/modules.txt
index 7c6c478..669bd9b 100644
--- a/src/vendor/modules.txt
+++ b/src/vendor/modules.txt
@@ -8,7 +8,7 @@
 golang.org/x/crypto/hkdf
 golang.org/x/crypto/internal/subtle
 golang.org/x/crypto/poly1305
-# golang.org/x/net v0.0.0-20201029202311-70d85028bad3
+# golang.org/x/net v0.0.0-20210129194117-4acb7895a057
 ## explicit
 golang.org/x/net/dns/dnsmessage
 golang.org/x/net/http/httpguts
diff --git a/test/fixedbugs/issue43570.go b/test/fixedbugs/issue43570.go
new file mode 100644
index 0000000..d073fde
--- /dev/null
+++ b/test/fixedbugs/issue43570.go
@@ -0,0 +1,40 @@
+// run
+
+// Copyright 2021 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"
+
+type T [8]*int
+
+//go:noinline
+func f(x int) T {
+	return T{}
+}
+
+//go:noinline
+func g(x int, t T) {
+	if t != (T{}) {
+		panic(fmt.Sprintf("bad: %v", t))
+	}
+}
+
+func main() {
+	const N = 10000
+	var q T
+	func() {
+		for i := 0; i < N; i++ {
+			q = f(0)
+			g(0, q)
+			sink = make([]byte, 1024)
+		}
+	}()
+	// Note that the closure is a trick to get the write to q to be a
+	// write to a pointer that is known to be non-nil and requires
+	// a write barrier.
+}
+
+var sink []byte