diff --git a/builtin/rebase.c b/builtin/rebase.c
index 1cd802dd92..19ad4df74f 100644
--- a/builtin/rebase.c
+++ b/builtin/rebase.c
@@ -1843,7 +1843,7 @@ int cmd_rebase(int argc,
 	strbuf_addf(&msg, "%s (start): checkout %s",
 		    options.reflog_action, options.onto_name);
 	ropts.oid = &options.onto->object.oid;
-	ropts.orig_head = &options.orig_head->object.oid,
+	ropts.orig_head = &options.orig_head->object.oid;
 	ropts.flags = RESET_HEAD_DETACH | RESET_ORIG_HEAD |
 			RESET_HEAD_RUN_POST_CHECKOUT_HOOK;
 	ropts.head_msg = msg.buf;
diff --git a/compat/regex/regex_internal.c b/compat/regex/regex_internal.c
index ec5cc5d2dd..4a4f849629 100644
--- a/compat/regex/regex_internal.c
+++ b/compat/regex/regex_internal.c
@@ -1232,7 +1232,10 @@ re_node_set_merge (re_node_set *dest, const re_node_set *src)
        is = src->nelem - 1, id = dest->nelem - 1; is >= 0 && id >= 0; )
     {
       if (dest->elems[id] == src->elems[is])
-	is--, id--;
+	{
+	  is--;
+	  id--;
+	}
       else if (dest->elems[id] < src->elems[is])
 	dest->elems[--sbase] = src->elems[is--];
       else /* if (dest->elems[id] > src->elems[is]) */
diff --git a/compat/regex/regexec.c b/compat/regex/regexec.c
index 2eeec82f40..c08f1bbe1f 100644
--- a/compat/regex/regexec.c
+++ b/compat/regex/regexec.c
@@ -2210,7 +2210,7 @@ sift_states_bkref (const re_match_context_t *mctx, re_sift_context_t *sctx,
 	  /* mctx->bkref_ents may have changed, reload the pointer.  */
 	  entry = mctx->bkref_ents + enabled_idx;
 	}
-      while (enabled_idx++, entry++->more);
+      while ((void)enabled_idx++, entry++->more);
     }
   err = REG_NOERROR;
  free_return:
diff --git a/config.mak.dev b/config.mak.dev
index 95b7bc46ae..e86b6e1b34 100644
--- a/config.mak.dev
+++ b/config.mak.dev
@@ -41,6 +41,10 @@ DEVELOPER_CFLAGS += -Wwrite-strings
 DEVELOPER_CFLAGS += -fno-common
 DEVELOPER_CFLAGS += -Wunreachable-code
 
+ifneq ($(filter clang9,$(COMPILER_FEATURES)),)
+DEVELOPER_CFLAGS += -Wcomma
+endif
+
 ifneq ($(filter clang4,$(COMPILER_FEATURES)),)
 DEVELOPER_CFLAGS += -Wtautological-constant-out-of-range-compare
 endif
diff --git a/detect-compiler b/detect-compiler
index a87650b71b..124ebdd4c9 100755
--- a/detect-compiler
+++ b/detect-compiler
@@ -9,7 +9,7 @@ CC="$*"
 #
 # FreeBSD clang version 3.4.1 (tags/RELEASE...)
 get_version_line() {
-	LANG=C LC_ALL=C $CC -v 2>&1 | grep ' version '
+	LANG=C LC_ALL=C $CC -v 2>&1 | sed -n '/ version /{p;q;}'
 }
 
 get_family() {
diff --git a/diff-delta.c b/diff-delta.c
index a4faf73829..71d37368d6 100644
--- a/diff-delta.c
+++ b/diff-delta.c
@@ -438,19 +438,31 @@ create_delta(const struct delta_index *index,
 			op = out + outpos++;
 			i = 0x80;
 
-			if (moff & 0x000000ff)
-				out[outpos++] = moff >> 0,  i |= 0x01;
-			if (moff & 0x0000ff00)
-				out[outpos++] = moff >> 8,  i |= 0x02;
-			if (moff & 0x00ff0000)
-				out[outpos++] = moff >> 16, i |= 0x04;
-			if (moff & 0xff000000)
-				out[outpos++] = moff >> 24, i |= 0x08;
+			if (moff & 0x000000ff) {
+				out[outpos++] = moff >> 0;
+				i |= 0x01;
+			}
+			if (moff & 0x0000ff00) {
+				out[outpos++] = moff >> 8;
+				i |= 0x02;
+			}
+			if (moff & 0x00ff0000) {
+				out[outpos++] = moff >> 16;
+				i |= 0x04;
+			}
+			if (moff & 0xff000000) {
+				out[outpos++] = moff >> 24;
+				i |= 0x08;
+			}
 
-			if (msize & 0x00ff)
-				out[outpos++] = msize >> 0, i |= 0x10;
-			if (msize & 0xff00)
-				out[outpos++] = msize >> 8, i |= 0x20;
+			if (msize & 0x00ff) {
+				out[outpos++] = msize >> 0;
+				i |= 0x10;
+			}
+			if (msize & 0xff00) {
+				out[outpos++] = msize >> 8;
+				i |= 0x20;
+			}
 
 			*op = i;
 
diff --git a/kwset.c b/kwset.c
index 1714eada60..064329434e 100644
--- a/kwset.c
+++ b/kwset.c
@@ -197,10 +197,13 @@ kwsincr (kwset_t kws, char const *text, size_t len)
       while (link && label != link->label)
 	{
 	  links[depth] = link;
-	  if (label < link->label)
-	    dirs[depth++] = L, link = link->llink;
-	  else
-	    dirs[depth++] = R, link = link->rlink;
+	  if (label < link->label) {
+	    dirs[depth++] = L;
+	    link = link->llink;
+	  } else {
+	    dirs[depth++] = R;
+	    link = link->rlink;
+	  }
 	}
 
       /* The current character doesn't have an outgoing link at
@@ -257,14 +260,14 @@ kwsincr (kwset_t kws, char const *text, size_t len)
 		  switch (dirs[depth + 1])
 		    {
 		    case L:
-		      r = links[depth], t = r->llink, rl = t->rlink;
-		      t->rlink = r, r->llink = rl;
+		      r = links[depth]; t = r->llink; rl = t->rlink;
+		      t->rlink = r; r->llink = rl;
 		      t->balance = r->balance = 0;
 		      break;
 		    case R:
-		      r = links[depth], l = r->llink, t = l->rlink;
-		      rl = t->rlink, lr = t->llink;
-		      t->llink = l, l->rlink = lr, t->rlink = r, r->llink = rl;
+		      r = links[depth]; l = r->llink; t = l->rlink;
+		      rl = t->rlink; lr = t->llink;
+		      t->llink = l; l->rlink = lr; t->rlink = r; r->llink = rl;
 		      l->balance = t->balance != 1 ? 0 : -1;
 		      r->balance = t->balance != (char) -1 ? 0 : 1;
 		      t->balance = 0;
@@ -277,14 +280,14 @@ kwsincr (kwset_t kws, char const *text, size_t len)
 		  switch (dirs[depth + 1])
 		    {
 		    case R:
-		      l = links[depth], t = l->rlink, lr = t->llink;
-		      t->llink = l, l->rlink = lr;
+		      l = links[depth]; t = l->rlink; lr = t->llink;
+		      t->llink = l; l->rlink = lr;
 		      t->balance = l->balance = 0;
 		      break;
 		    case L:
-		      l = links[depth], r = l->rlink, t = r->llink;
-		      lr = t->llink, rl = t->rlink;
-		      t->llink = l, l->rlink = lr, t->rlink = r, r->llink = rl;
+		      l = links[depth]; r = l->rlink; t = r->llink;
+		      lr = t->llink; rl = t->rlink;
+		      t->llink = l; l->rlink = lr; t->rlink = r; r->llink = rl;
 		      l->balance = t->balance != 1 ? 0 : -1;
 		      r->balance = t->balance != (char) -1 ? 0 : 1;
 		      t->balance = 0;
@@ -567,22 +570,22 @@ bmexec (kwset_t kws, char const *text, size_t size)
       {
 	while (tp <= ep)
 	  {
-	    d = d1[U(tp[-1])], tp += d;
-	    d = d1[U(tp[-1])], tp += d;
+	    d = d1[U(tp[-1])]; tp += d;
+	    d = d1[U(tp[-1])]; tp += d;
 	    if (d == 0)
 	      goto found;
-	    d = d1[U(tp[-1])], tp += d;
-	    d = d1[U(tp[-1])], tp += d;
-	    d = d1[U(tp[-1])], tp += d;
+	    d = d1[U(tp[-1])]; tp += d;
+	    d = d1[U(tp[-1])]; tp += d;
+	    d = d1[U(tp[-1])]; tp += d;
 	    if (d == 0)
 	      goto found;
-	    d = d1[U(tp[-1])], tp += d;
-	    d = d1[U(tp[-1])], tp += d;
-	    d = d1[U(tp[-1])], tp += d;
+	    d = d1[U(tp[-1])]; tp += d;
+	    d = d1[U(tp[-1])]; tp += d;
+	    d = d1[U(tp[-1])]; tp += d;
 	    if (d == 0)
 	      goto found;
-	    d = d1[U(tp[-1])], tp += d;
-	    d = d1[U(tp[-1])], tp += d;
+	    d = d1[U(tp[-1])]; tp += d;
+	    d = d1[U(tp[-1])]; tp += d;
 	  }
 	break;
       found:
@@ -649,7 +652,8 @@ cwexec (kwset_t kws, char const *text, size_t len, struct kwsmatch *kwsmatch)
     mch = NULL;
   else
     {
-      mch = text, accept = kwset->trie;
+      mch = text;
+      accept = kwset->trie;
       goto match;
     }
 
diff --git a/meson.build b/meson.build
index 9f3b5ad676..fe930cedc9 100644
--- a/meson.build
+++ b/meson.build
@@ -715,6 +715,7 @@ libgit_dependencies = [ ]
 # Makefile.
 if get_option('warning_level') in ['2','3', 'everything'] and compiler.get_argument_syntax() == 'gcc'
   foreach cflag : [
+    '-Wcomma',
     '-Wdeclaration-after-statement',
     '-Wformat-security',
     '-Wold-style-definition',
diff --git a/remote-curl.c b/remote-curl.c
index 1273507a96..590b228f67 100644
--- a/remote-curl.c
+++ b/remote-curl.c
@@ -1239,7 +1239,7 @@ static int fetch_git(struct discovery *heads,
 	packet_buf_flush(&preamble);
 
 	memset(&rpc, 0, sizeof(rpc));
-	rpc.service_name = "git-upload-pack",
+	rpc.service_name = "git-upload-pack";
 	rpc.gzip_request = 1;
 
 	err = rpc_service(&rpc, heads, args.v, &preamble, &rpc_result);
@@ -1401,7 +1401,7 @@ static int push_git(struct discovery *heads, int nr_spec, const char **specs)
 	packet_buf_flush(&preamble);
 
 	memset(&rpc, 0, sizeof(rpc));
-	rpc.service_name = "git-receive-pack",
+	rpc.service_name = "git-receive-pack";
 
 	err = rpc_service(&rpc, heads, args.v, &preamble, &rpc_result);
 	if (rpc_result.len)
diff --git a/t/unit-tests/clar/clar/fs.h b/t/unit-tests/clar/clar/fs.h
index 8b206179fc..2203743fb4 100644
--- a/t/unit-tests/clar/clar/fs.h
+++ b/t/unit-tests/clar/clar/fs.h
@@ -376,9 +376,12 @@ fs_copydir_helper(const char *source, const char *dest, int dest_mode)
 	mkdir(dest, dest_mode);
 
 	cl_assert_(source_dir = opendir(source), "Could not open source dir");
-	while ((d = (errno = 0, readdir(source_dir))) != NULL) {
+	for (;;) {
 		char *child;
 
+		errno = 0;
+		if ((d = readdir(source_dir)) == NULL)
+			break;
 		if (!strcmp(d->d_name, ".") || !strcmp(d->d_name, ".."))
 			continue;
 
@@ -479,9 +482,12 @@ fs_rmdir_helper(const char *path)
 	struct dirent *d;
 
 	cl_assert_(dir = opendir(path), "Could not open dir");
-	while ((d = (errno = 0, readdir(dir))) != NULL) {
+	for (;;) {
 		char *child;
 
+		errno = 0;
+		if ((d = readdir(dir)) == NULL)
+			break;
 		if (!strcmp(d->d_name, ".") || !strcmp(d->d_name, ".."))
 			continue;
 
diff --git a/wildmatch.c b/wildmatch.c
index 8ea29141bd..69a2ae7000 100644
--- a/wildmatch.c
+++ b/wildmatch.c
@@ -223,7 +223,7 @@ static int dowild(const uchar *p, const uchar *text, unsigned int flags)
 						p_ch = '[';
 						if (t_ch == p_ch)
 							matched = 1;
-						continue;
+						goto next;
 					}
 					if (CC_EQ(s,i, "alnum")) {
 						if (ISALNUM(t_ch))
@@ -268,7 +268,10 @@ static int dowild(const uchar *p, const uchar *text, unsigned int flags)
 					p_ch = 0; /* This makes "prev_ch" get set to 0. */
 				} else if (t_ch == p_ch)
 					matched = 1;
-			} while (prev_ch = p_ch, (p_ch = *++p) != ']');
+next:
+				prev_ch = p_ch;
+				p_ch = *++p;
+			} while (p_ch != ']');
 			if (matched == negated ||
 			    ((flags & WM_PATHNAME) && t_ch == '/'))
 				return WM_NOMATCH;
diff --git a/xdiff/xdiffi.c b/xdiff/xdiffi.c
index 8889b8b62a..5a96e36dfb 100644
--- a/xdiff/xdiffi.c
+++ b/xdiff/xdiffi.c
@@ -211,8 +211,10 @@ static long xdl_split(unsigned long const *ha1, long off1, long lim1,
 			for (d = fmax; d >= fmin; d -= 2) {
 				i1 = XDL_MIN(kvdf[d], lim1);
 				i2 = i1 - d;
-				if (lim2 < i2)
-					i1 = lim2 + d, i2 = lim2;
+				if (lim2 < i2) {
+					i1 = lim2 + d;
+					i2 = lim2;
+				}
 				if (fbest < i1 + i2) {
 					fbest = i1 + i2;
 					fbest1 = i1;
@@ -223,8 +225,10 @@ static long xdl_split(unsigned long const *ha1, long off1, long lim1,
 			for (d = bmax; d >= bmin; d -= 2) {
 				i1 = XDL_MAX(off1, kvdb[d]);
 				i2 = i1 - d;
-				if (i2 < off2)
-					i1 = off2 + d, i2 = off2;
+				if (i2 < off2) {
+					i1 = off2 + d;
+					i2 = off2;
+				}
 				if (i1 + i2 < bbest) {
 					bbest = i1 + i2;
 					bbest1 = i1;