Prefer signed when testing for signed overflow

* src/alloc.c (free_cons):
* src/casefiddle.c (do_casify_multibyte_string):
* src/editfns.c (styled_format):
* src/image.c (png_load_body):
Use signed arguments to INT_MULTIPLY_WRAPV etc.  This doesn’t fix
any bugs, but GCC emits better code when all args are signed.
Also, this removes the need for an if in free_cons (Bug#37006).

1 files changed, 2 insertions, 2 deletions

diff --git a/src/image.c b/src/image.c
index 81d8cb4e2b2..a59be0cd8ff 100644
--- a/src/image.c
+++ b/src/image.c
@@ -6463,7 +6463,6 @@ png_load_body (struct frame *f, struct image *img, struct png_load_context *c)
   png_uint_32 row_bytes;
   bool transparent_p;
   struct png_memory_storage tbr;  /* Data to be read */
-  ptrdiff_t nbytes;
   Emacs_Pix_Container ximg, mask_img = NULL;
 
   /* Find out what file to load.  */
@@ -6660,7 +6659,8 @@ png_load_body (struct frame *f, struct image *img, struct png_load_context *c)
   row_bytes = png_get_rowbytes (png_ptr, info_ptr);
 
   /* Allocate memory for the image.  */
-  if (INT_MULTIPLY_WRAPV (row_bytes, sizeof *pixels, &nbytes)
+  ptrdiff_t nbytes = sizeof *pixels;
+  if (INT_MULTIPLY_WRAPV (row_bytes, nbytes, &nbytes)
       || INT_MULTIPLY_WRAPV (nbytes, height, &nbytes))
     memory_full (SIZE_MAX);
   c->pixels = pixels = xmalloc (nbytes);