[PATCH 04/14] calloc, malloc: tune a bit

[Paul Eggert]

This applies mostly to non-glibc platforms, or to 32-bit
glibc before glibc 2.30 (2019).
* lib/calloc.c (rpl_calloc):
* lib/malloc.c (rpl_malloc):
Optimize away some of the code if !HAVE_MALLOC_0_NONNULL or if
!HAVE_MALLOC_PTRDIFF.
* m4/malloc.m4 (gl_FUNC_MALLOC_GNU): Define HAVE_MALLOC_0_NONNULL.
(gl_FUNC_MALLOC_PTRDIFF): Define HAVE_MALLOC_PTRDIFF.
---
 ChangeLog    | 10 ++++++++++
 lib/calloc.c |  4 ++++
 lib/malloc.c |  4 ++++
 m4/malloc.m4 | 22 ++++++++++++++--------
 4 files changed, 32 insertions(+), 8 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index f12ca64f17..5edadc4ea8 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,15 @@
 2024-11-04  Paul Eggert  <egg...@cs.ucla.edu>
 
+       calloc, malloc: tune a bit
+       This applies mostly to non-glibc platforms, or to 32-bit
+       glibc before glibc 2.30 (2019).
+       * lib/calloc.c (rpl_calloc):
+       * lib/malloc.c (rpl_malloc):
+       Optimize away some of the code if !HAVE_MALLOC_0_NONNULL or if
+       !HAVE_MALLOC_PTRDIFF.
+       * m4/malloc.m4 (gl_FUNC_MALLOC_GNU): Define HAVE_MALLOC_0_NONNULL.
+       (gl_FUNC_MALLOC_PTRDIFF): Define HAVE_MALLOC_PTRDIFF.
+
        calloc: configure more like malloc
        * m4/calloc.m4 (gl_FUNC_CALLOC_IF): Rename from _AC_FUNC_CALLOC_IF
        since this is not derived from Autoconf.  All uses changed.
diff --git a/lib/calloc.c b/lib/calloc.c
index 801b672078..124c1f9958 100644
--- a/lib/calloc.c
+++ b/lib/calloc.c
@@ -34,15 +34,19 @@
 void *
 rpl_calloc (size_t n, size_t s)
 {
+#if !HAVE_MALLOC_0_NONNULL
   if (n == 0 || s == 0)
     n = s = 1;
+#endif
 
+#if !HAVE_MALLOC_PTRDIFF
   ptrdiff_t signed_n;
   if (ckd_mul (&signed_n, n, s))
     {
       errno = ENOMEM;
       return NULL;
     }
+#endif
 
   void *result = calloc (n, s);
 
diff --git a/lib/malloc.c b/lib/malloc.c
index 90018863ea..fdb5348268 100644
--- a/lib/malloc.c
+++ b/lib/malloc.c
@@ -30,15 +30,19 @@
 void *
 rpl_malloc (size_t n)
 {
+#if !HAVE_MALLOC_0_NONNULL
   if (n == 0)
     n = 1;
+#endif
 
+#if !HAVE_MALLOC_PTRDIFF
   ptrdiff_t signed_n;
   if (ckd_add (&signed_n, n, 0))
     {
       errno = ENOMEM;
       return NULL;
     }
+#endif
 
   void *result = malloc (n);
 
diff --git a/m4/malloc.m4 b/m4/malloc.m4
index 657eed779c..deb0de24de 100644
--- a/m4/malloc.m4
+++ b/m4/malloc.m4
@@ -1,5 +1,5 @@
 # malloc.m4
-# serial 40
+# serial 41
 dnl Copyright (C) 2007, 2009-2024 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
@@ -45,6 +45,7 @@ AC_DEFUN([_AC_FUNC_MALLOC_IF],
 
 # gl_FUNC_MALLOC_GNU
 # ------------------
+# Define HAVE_MALLOC_0_NONNULL if malloc (0) returns nonnull.
 # Replace malloc if it is not compatible with GNU libc.
 AC_DEFUN([gl_FUNC_MALLOC_GNU],
 [
@@ -55,11 +56,12 @@ AC_DEFUN([gl_FUNC_MALLOC_GNU],
   dnl gets defined already before this macro gets invoked.  This helps
   dnl if !(__VEC__ || __AIXVEC), and doesn't hurt otherwise.
 
-  REPLACE_MALLOC_FOR_MALLOC_GNU="$REPLACE_MALLOC_FOR_MALLOC_POSIX"
-  if test $REPLACE_MALLOC_FOR_MALLOC_GNU = 0; then
-    _AC_FUNC_MALLOC_IF([], [REPLACE_MALLOC_FOR_MALLOC_GNU=1],
-      ["$gl_cross_guess_normal"])
-  fi
+  _AC_FUNC_MALLOC_IF(
+    [AC_DEFINE([HAVE_MALLOC_0_NONNULL], [1],
+       [Define to 1 if malloc (0) returns nonnull.])
+     REPLACE_MALLOC_FOR_MALLOC_GNU=$REPLACE_MALLOC_FOR_MALLOC_POSIX],
+    [REPLACE_MALLOC_FOR_MALLOC_GNU=1],
+    ["$gl_cross_guess_normal"])
 ])
 
 # gl_FUNC_MALLOC_PTRDIFF
@@ -70,12 +72,16 @@ AC_DEFUN([gl_FUNC_MALLOC_PTRDIFF],
 [
   AC_REQUIRE([gl_STDLIB_H_DEFAULTS])
   AC_REQUIRE([gl_CHECK_MALLOC_PTRDIFF])
-  test "$gl_cv_malloc_ptrdiff" = yes || REPLACE_MALLOC_FOR_MALLOC_POSIX=1
+  AS_IF([test "$gl_cv_malloc_ptrdiff" = yes],
+    [AC_DEFINE([HAVE_MALLOC_PTRDIFF], 1,
+       [Define to 1 if malloc-like functions do not allocate objects
+        larger than PTRDIFF_MAX bytes.])],
+    [REPLACE_MALLOC_FOR_MALLOC_POSIX=1])
 ])
 
 # Test whether malloc, realloc, calloc refuse to create objects
 # larger than what can be expressed in ptrdiff_t.
-# Set gl_cv_func_malloc_gnu to yes or no accordingly.
+# Set gl_cv_func_malloc_gnu and define MALLOC_PTRDIFF accordingly.
 AC_DEFUN([gl_CHECK_MALLOC_PTRDIFF],
 [
   AC_CACHE_CHECK([whether malloc is ptrdiff_t safe],
-- 
2.43.0