diff --git a/include/verify.h b/include/verify.h
index 00e78d3f8c..c3db0e3c72 100644
--- a/include/verify.h
+++ b/include/verify.h
@@ -1,2 +1,4 @@
 /* Gnulib <verify.h>, simplified by assuming GCC 4.6 or later.  */
 #define verify(R) _Static_assert (R, "verify (" #R ")")
+
+#define assume(R) ((R) ? (void) 0 : __builtin_unreachable ())
diff --git a/posix/regcomp.c b/posix/regcomp.c
index 7525355a9b..3e8f1e6107 100644
--- a/posix/regcomp.c
+++ b/posix/regcomp.c
@@ -1436,7 +1436,7 @@ link_nfa_nodes (void *extra, bin_tree_t *node)
       break;
 
     case END_OF_RE:
-      assert (node->next == NULL);
+      DEBUG_ASSERT (node->next == NULL);
       break;
 
     case OP_DUP_ASTERISK:
@@ -1452,8 +1452,8 @@ link_nfa_nodes (void *extra, bin_tree_t *node)
 	  right = node->right->first->node_idx;
 	else
 	  right = node->next->node_idx;
-	assert (left > -1);
-	assert (right > -1);
+	DEBUG_ASSERT (left > -1);
+	DEBUG_ASSERT (right > -1);
 	err = re_node_set_init_2 (dfa->edests + idx, left, right);
       }
       break;
@@ -1471,7 +1471,7 @@ link_nfa_nodes (void *extra, bin_tree_t *node)
       break;
 
     default:
-      assert (!IS_EPSILON_NODE (node->token.type));
+      DEBUG_ASSERT (!IS_EPSILON_NODE (node->token.type));
       dfa->nexts[idx] = node->next->node_idx;
       break;
     }
@@ -1653,9 +1653,7 @@ calc_eclosure (re_dfa_t *dfa)
 {
   Idx node_idx;
   bool incomplete;
-#ifdef DEBUG
-  assert (dfa->nodes_len > 0);
-#endif
+  DEBUG_ASSERT (dfa->nodes_len > 0);
   incomplete = false;
   /* For each nodes, calculate epsilon closure.  */
   for (node_idx = 0; ; ++node_idx)
@@ -1670,9 +1668,7 @@ calc_eclosure (re_dfa_t *dfa)
 	  node_idx = 0;
 	}
 
-#ifdef DEBUG
-      assert (dfa->eclosures[node_idx].nelem != -1);
-#endif
+      DEBUG_ASSERT (dfa->eclosures[node_idx].nelem != -1);
 
       /* If we have already calculated, skip it.  */
       if (dfa->eclosures[node_idx].nelem != 0)
@@ -2442,9 +2438,7 @@ parse_expression (re_string_t *regexp, regex_t *preg, re_token_t *token,
 
     default:
       /* Must not happen?  */
-#ifdef DEBUG
-      assert (0);
-#endif
+      DEBUG_ASSERT (false);
       return NULL;
     }
   fetch_token (token, regexp, syntax);
@@ -3306,7 +3300,7 @@ parse_bracket_exp (re_string_t *regexp, re_dfa_t *dfa, re_token_t *token,
 	       goto parse_bracket_exp_free_return;
 	      break;
 	    default:
-	      assert (0);
+	      DEBUG_ASSERT (false);
 	      break;
 	    }
 	}
@@ -3662,7 +3656,6 @@ build_charclass_op (re_dfa_t *dfa, RE_TRANSLATE_TYPE trans,
   Idx alloc = 0;
 #endif /* not RE_ENABLE_I18N */
   reg_errcode_t ret;
-  re_token_t br_token;
   bin_tree_t *tree;
 
   sbcset = (re_bitset_ptr_t) calloc (sizeof (bitset_t), 1);
@@ -3713,11 +3706,7 @@ build_charclass_op (re_dfa_t *dfa, RE_TRANSLATE_TYPE trans,
 #endif
 
   /* Build a tree for simple bracket.  */
-#if defined GCC_LINT || defined lint
-  memset (&br_token, 0, sizeof br_token);
-#endif
-  br_token.type = SIMPLE_BRACKET;
-  br_token.opr.sbcset = sbcset;
+  re_token_t br_token = { .type = SIMPLE_BRACKET, .opr.sbcset = sbcset };
   tree = create_token_tree (dfa, NULL, NULL, &br_token);
   if (__glibc_unlikely (tree == NULL))
     goto build_word_op_espace;
@@ -3808,11 +3797,7 @@ static bin_tree_t *
 create_tree (re_dfa_t *dfa, bin_tree_t *left, bin_tree_t *right,
 	     re_token_type_t type)
 {
-  re_token_t t;
-#if defined GCC_LINT || defined lint
-  memset (&t, 0, sizeof t);
-#endif
-  t.type = type;
+  re_token_t t = { .type = type };
   return create_token_tree (dfa, left, right, &t);
 }
 
diff --git a/posix/regex_internal.c b/posix/regex_internal.c
index 99fbb26ecb..6aa9116084 100644
--- a/posix/regex_internal.c
+++ b/posix/regex_internal.c
@@ -212,7 +212,7 @@ build_wcs_buffer (re_string_t *pstr)
 {
 #ifdef _LIBC
   unsigned char buf[MB_LEN_MAX];
-  assert (MB_LEN_MAX >= pstr->mb_cur_max);
+  DEBUG_ASSERT (MB_LEN_MAX >= pstr->mb_cur_max);
 #else
   unsigned char buf[64];
 #endif
@@ -285,7 +285,7 @@ build_wcs_upper_buffer (re_string_t *pstr)
   size_t mbclen;
 #ifdef _LIBC
   char buf[MB_LEN_MAX];
-  assert (MB_LEN_MAX >= pstr->mb_cur_max);
+  DEBUG_ASSERT (pstr->mb_cur_max <= MB_LEN_MAX);
 #else
   char buf[64];
 #endif
@@ -685,9 +685,7 @@ re_string_reconstruct (re_string_t *pstr, Idx idx, int eflags)
 			 pstr->valid_len - offset);
 	      pstr->valid_len -= offset;
 	      pstr->valid_raw_len -= offset;
-#if defined DEBUG && DEBUG
-	      assert (pstr->valid_len > 0);
-#endif
+	      DEBUG_ASSERT (pstr->valid_len > 0);
 	    }
 	}
       else
@@ -941,10 +939,7 @@ re_string_context_at (const re_string_t *input, Idx idx, int eflags)
       Idx wc_idx = idx;
       while(input->wcs[wc_idx] == WEOF)
 	{
-#if defined DEBUG && DEBUG
-	  /* It must not happen.  */
-	  assert (wc_idx >= 0);
-#endif
+	  DEBUG_ASSERT (wc_idx >= 0);
 	  --wc_idx;
 	  if (wc_idx < 0)
 	    return input->tip_context;
diff --git a/posix/regex_internal.h b/posix/regex_internal.h
index 5462419b78..06957f0fc8 100644
--- a/posix/regex_internal.h
+++ b/posix/regex_internal.h
@@ -20,7 +20,6 @@
 #ifndef _REGEX_INTERNAL_H
 #define _REGEX_INTERNAL_H 1
 
-#include <assert.h>
 #include <ctype.h>
 #include <stdio.h>
 #include <stdlib.h>
@@ -34,6 +33,14 @@
 #include <stdint.h>
 
 #include <intprops.h>
+#include <verify.h>
+
+#if defined DEBUG && DEBUG != 0
+# include <assert.h>
+# define DEBUG_ASSERT(x) assert (x)
+#else
+# define DEBUG_ASSERT(x) assume (x)
+#endif
 
 #ifdef _LIBC
 # include <libc-lock.h>
@@ -44,22 +51,7 @@
 # define lock_unlock(lock) __libc_lock_unlock (lock)
 #elif defined GNULIB_LOCK && !defined USE_UNLOCKED_IO
 # include "glthread/lock.h"
-  /* Use gl_lock_define if empty macro arguments are known to work.
-     Otherwise, fall back on less-portable substitutes.  */
-# if ((defined __GNUC__ && !defined __STRICT_ANSI__) \
-      || (defined __STDC_VERSION__ && 199901L <= __STDC_VERSION__))
-#  define lock_define(name) gl_lock_define (, name)
-# elif USE_POSIX_THREADS
-#  define lock_define(name) pthread_mutex_t name;
-# elif USE_PTH_THREADS
-#  define lock_define(name) pth_mutex_t name;
-# elif USE_SOLARIS_THREADS
-#  define lock_define(name) mutex_t name;
-# elif USE_WINDOWS_THREADS
-#  define lock_define(name) gl_lock_t name;
-# else
-#  define lock_define(name)
-# endif
+# define lock_define(name) gl_lock_define (, name)
 # define lock_init(lock) glthread_lock_init (&(lock))
 # define lock_fini(lock) glthread_lock_destroy (&(lock))
 # define lock_lock(lock) glthread_lock_lock (&(lock))
@@ -618,11 +610,7 @@ typedef struct
 {
   /* The string object corresponding to the input string.  */
   re_string_t input;
-#if defined _LIBC || (defined __STDC_VERSION__ && __STDC_VERSION__ >= 199901L)
   const re_dfa_t *const dfa;
-#else
-  const re_dfa_t *dfa;
-#endif
   /* EFLAGS of the argument of regexec.  */
   int eflags;
   /* Where the matching ends.  */
diff --git a/posix/regexec.c b/posix/regexec.c
index 4ff30a79c0..3c46ac81dd 100644
--- a/posix/regexec.c
+++ b/posix/regexec.c
@@ -443,7 +443,7 @@ re_search_stub (struct re_pattern_buffer *bufp, const char *string, Idx length,
     {
       if (ret_len)
 	{
-	  assert (pmatch[0].rm_so == start);
+	  DEBUG_ASSERT (pmatch[0].rm_so == start);
 	  rval = pmatch[0].rm_eo - start;
 	}
       else
@@ -502,9 +502,9 @@ re_copy_regs (struct re_registers *regs, regmatch_t *pmatch, Idx nregs,
     }
   else
     {
-      assert (regs_allocated == REGS_FIXED);
+      DEBUG_ASSERT (regs_allocated == REGS_FIXED);
       /* This function may not be called with REGS_FIXED and nregs too big.  */
-      assert (regs->num_regs >= nregs);
+      DEBUG_ASSERT (nregs <= regs->num_regs);
       rval = REGS_FIXED;
     }
 
@@ -597,21 +597,12 @@ re_search_internal (const regex_t *preg, const char *string, Idx length,
   Idx extra_nmatch;
   bool sb;
   int ch;
-#if defined _LIBC || (defined __STDC_VERSION__ && __STDC_VERSION__ >= 199901L)
   re_match_context_t mctx = { .dfa = dfa };
-#else
-  re_match_context_t mctx;
-#endif
   char *fastmap = ((preg->fastmap != NULL && preg->fastmap_accurate
 		    && start != last_start && !preg->can_be_null)
 		   ? preg->fastmap : NULL);
   RE_TRANSLATE_TYPE t = preg->translate;
 
-#if !(defined _LIBC || (defined __STDC_VERSION__ && __STDC_VERSION__ >= 199901L))
-  memset (&mctx, '\0', sizeof (re_match_context_t));
-  mctx.dfa = dfa;
-#endif
-
   extra_nmatch = (nmatch > preg->re_nsub) ? nmatch - (preg->re_nsub + 1) : 0;
   nmatch -= extra_nmatch;
 
@@ -622,10 +613,8 @@ re_search_internal (const regex_t *preg, const char *string, Idx length,
 			|| dfa->init_state_begbuf == NULL))
     return REG_NOMATCH;
 
-#ifdef DEBUG
   /* We assume front-end functions already check them.  */
-  assert (0 <= last_start && last_start <= length);
-#endif
+  DEBUG_ASSERT (0 <= last_start && last_start <= length);
 
   /* If initial states with non-begbuf contexts have no elements,
      the regex must be anchored.  If preg->newline_anchor is set,
@@ -677,8 +666,6 @@ re_search_internal (const regex_t *preg, const char *string, Idx length,
 	  goto free_return;
 	}
     }
-  else
-    mctx.state_log = NULL;
 
   match_first = start;
   mctx.input.tip_context = (eflags & REG_NOTBOL) ? CONTEXT_BEGBUF
@@ -838,10 +825,8 @@ re_search_internal (const regex_t *preg, const char *string, Idx length,
       match_ctx_clean (&mctx);
     }
 
-#ifdef DEBUG
-  assert (match_last != -1);
-  assert (err == REG_NOERROR);
-#endif
+  DEBUG_ASSERT (match_last != -1);
+  DEBUG_ASSERT (err == REG_NOERROR);
 
   /* Set pmatch[] if we need.  */
   if (nmatch > 0)
@@ -886,7 +871,7 @@ re_search_internal (const regex_t *preg, const char *string, Idx length,
 		   : mctx.input.offsets[pmatch[reg_idx].rm_eo]);
 	      }
 #else
-	    assert (mctx.input.offsets_needed == 0);
+	    DEBUG_ASSERT (mctx.input.offsets_needed == 0);
 #endif
 	    pmatch[reg_idx].rm_so += match_first;
 	    pmatch[reg_idx].rm_eo += match_first;
@@ -926,9 +911,7 @@ prune_impossible_nodes (re_match_context_t *mctx)
   re_dfastate_t **sifted_states;
   re_dfastate_t **lim_states = NULL;
   re_sift_context_t sctx;
-#ifdef DEBUG
-  assert (mctx->state_log != NULL);
-#endif
+  DEBUG_ASSERT (mctx->state_log != NULL);
   match_last = mctx->match_last;
   halt_node = mctx->last_node;
 
@@ -1074,7 +1057,7 @@ check_matching (re_match_context_t *mctx, bool fl_longest_match,
   /* An initial state must not be NULL (invalid).  */
   if (__glibc_unlikely (cur_state == NULL))
     {
-      assert (err == REG_ESPACE);
+      DEBUG_ASSERT (err == REG_ESPACE);
       return -2;
     }
 
@@ -1129,7 +1112,7 @@ check_matching (re_match_context_t *mctx, bool fl_longest_match,
 	  err = extend_buffers (mctx, next_char_idx + 1);
 	  if (__glibc_unlikely (err != REG_NOERROR))
 	    {
-	      assert (err == REG_ESPACE);
+	      DEBUG_ASSERT (err == REG_ESPACE);
 	      return -2;
 	    }
 	}
@@ -1212,9 +1195,7 @@ check_halt_state_context (const re_match_context_t *mctx,
 {
   Idx i;
   unsigned int context;
-#ifdef DEBUG
-  assert (state->halt);
-#endif
+  DEBUG_ASSERT (state->halt);
   context = re_string_context_at (&mctx->input, idx, mctx->eflags);
   for (i = 0; i < state->nodes.nelem; ++i)
     if (check_halt_node_context (mctx->dfa, state->nodes.elems[i], context))
@@ -1362,7 +1343,7 @@ pop_fail_stack (struct re_fail_stack_t *fs, Idx *pidx, Idx nregs,
 		regmatch_t *regs, re_node_set *eps_via_nodes)
 {
   Idx num = --fs->num;
-  assert (num >= 0);
+  DEBUG_ASSERT (num >= 0);
   *pidx = fs->stack[num].idx;
   memcpy (regs, fs->stack[num].regs, sizeof (regmatch_t) * nregs);
   re_node_set_free (eps_via_nodes);
@@ -1389,10 +1370,8 @@ set_regs (const regex_t *preg, const re_match_context_t *mctx, size_t nmatch,
   regmatch_t *prev_idx_match;
   bool prev_idx_match_malloced = false;
 
-#ifdef DEBUG
-  assert (nmatch > 1);
-  assert (mctx->state_log != NULL);
-#endif
+  DEBUG_ASSERT (nmatch > 1);
+  DEBUG_ASSERT (mctx->state_log != NULL);
   if (fl_backtrack)
     {
       fs = &fs_body;
@@ -1578,9 +1557,7 @@ sift_states_backward (const re_match_context_t *mctx, re_sift_context_t *sctx)
   Idx str_idx = sctx->last_str_idx;
   re_node_set cur_dest;
 
-#ifdef DEBUG
-  assert (mctx->state_log != NULL && mctx->state_log[str_idx] != NULL);
-#endif
+  DEBUG_ASSERT (mctx->state_log != NULL && mctx->state_log[str_idx] != NULL);
 
   /* Build sifted state_log[str_idx].  It has the nodes which can epsilon
      transit to the last_node and the last_node itself.  */
@@ -1648,11 +1625,8 @@ build_sifted_states (const re_match_context_t *mctx, re_sift_context_t *sctx,
       Idx prev_node = cur_src->elems[i];
       int naccepted = 0;
       bool ok;
+      DEBUG_ASSERT (!IS_EPSILON_NODE (dfa->nodes[prev_node].type));
 
-#ifdef DEBUG
-      re_token_type_t type = dfa->nodes[prev_node].type;
-      assert (!IS_EPSILON_NODE (type));
-#endif
 #ifdef RE_ENABLE_I18N
       /* If the node may accept "multi byte".  */
       if (dfa->nodes[prev_node].accept_mb)
@@ -2505,9 +2479,7 @@ transit_state_mb (re_match_context_t *mctx, re_dfastate_t *pstate)
       err = clean_state_log_if_needed (mctx, dest_idx);
       if (__glibc_unlikely (err != REG_NOERROR))
 	return err;
-#ifdef DEBUG
-      assert (dfa->nexts[cur_node_idx] != -1);
-#endif
+      DEBUG_ASSERT (dfa->nexts[cur_node_idx] != -1);
       new_nodes = dfa->eclosures + dfa->nexts[cur_node_idx];
 
       dest_state = mctx->state_log[dest_idx];
@@ -2571,9 +2543,7 @@ transit_state_bkref (re_match_context_t *mctx, const re_node_set *nodes)
 
       /* And add the epsilon closures (which is 'new_dest_nodes') of
 	 the backreference to appropriate state_log.  */
-#ifdef DEBUG
-      assert (dfa->nexts[node_idx] != -1);
-#endif
+      DEBUG_ASSERT (dfa->nexts[node_idx] != -1);
       for (; bkc_idx < mctx->nbkref_ents; ++bkc_idx)
 	{
 	  Idx subexp_len;
@@ -3032,10 +3002,8 @@ check_arrival_add_next_nodes (re_match_context_t *mctx, Idx str_idx,
     {
       int naccepted = 0;
       Idx cur_node = cur_nodes->elems[cur_idx];
-#ifdef DEBUG
-      re_token_type_t type = dfa->nodes[cur_node].type;
-      assert (!IS_EPSILON_NODE (type));
-#endif
+      DEBUG_ASSERT (!IS_EPSILON_NODE (dfa->nodes[cur_node].type));
+
 #ifdef RE_ENABLE_I18N
       /* If the node may accept "multi byte".  */
       if (dfa->nodes[cur_node].accept_mb)
@@ -3103,9 +3071,7 @@ check_arrival_expand_ecl (const re_dfa_t *dfa, re_node_set *cur_nodes,
   reg_errcode_t err;
   Idx idx, outside_node;
   re_node_set new_nodes;
-#ifdef DEBUG
-  assert (cur_nodes->nelem);
-#endif
+  DEBUG_ASSERT (cur_nodes->nelem);
   err = re_node_set_alloc (&new_nodes, cur_nodes->nelem);
   if (__glibc_unlikely (err != REG_NOERROR))
     return err;
@@ -3695,6 +3661,7 @@ group_nodes_into_DFAstates (const re_dfa_t *dfa, const re_dfastate_t *state,
 	  bitset_empty (accepts);
 	}
     }
+  assume (ndests <= SBC_MAX);
   return ndests;
  error_return:
   for (j = 0; j < ndests; ++j)
@@ -4272,10 +4239,8 @@ static reg_errcode_t
 __attribute_warn_unused_result__
 match_ctx_add_subtop (re_match_context_t *mctx, Idx node, Idx str_idx)
 {
-#ifdef DEBUG
-  assert (mctx->sub_tops != NULL);
-  assert (mctx->asub_tops > 0);
-#endif
+  DEBUG_ASSERT (mctx->sub_tops != NULL);
+  DEBUG_ASSERT (mctx->asub_tops > 0);
   if (__glibc_unlikely (mctx->nsub_tops == mctx->asub_tops))
     {
       Idx new_asub_tops = mctx->asub_tops * 2;
