Created attachment 2119241 [details]
Test input image

From https://github.com/janko/image_processing/blob/8185ea61518d8cf477594505cd4b5ab478b28aea/test/fixtures/portrait.jpg

ruby test case:
https://github.com/janko/image_processing/blob/8185ea61518d8cf477594505cd4b5ab478b28aea/test/vips_test.rb#L177-L181

And in C:
resize-to-limit-test.c

```
#include <stdlib.h>
#include <stdio.h>
#include <glib.h>
#include <vips/vips.h>
#include <sys/stat.h>

#define MY_ASSERT(expr) \
do { \
	if (!(expr)) { \
		fprintf(stderr, "LINE[%d] : assertion \"" #expr "\" failed.\n", __LINE__); \
		abort(); \
	} \
} while(0)


int main(void) {
	VipsImage *normal_image, *sharpened_image, *tmp_image;
	VipsImage *sharpen_mask_image;
	int ret;

#define MASK_WIDTH  (3)
#define MASK_HEIGHT (3)
#define MASK_DIMENSION (MASK_WIDTH * MASK_HEIGHT)

	static const int sharpen_array_2d_int[MASK_WIDTH][MASK_HEIGHT] = {
		{-1, -1, -1,},
		{-1, 32, -1,},
		{-1, -1, -1},
	};
	static double sharpen_array_1d_double[MASK_DIMENSION];
	const char *input_path = "./portrait.jpg";

	ret = vips_thumbnail(
			input_path, &normal_image,
			400,
			"height", 400,
			"size", VIPS_SIZE_DOWN,
			NULL
		);
	MY_ASSERT(!ret);
	ret = vips_thumbnail(
			input_path, &tmp_image,
			400,
			"height", 400,
			"size", VIPS_SIZE_DOWN,
			NULL
		);
	MY_ASSERT(!ret);

	for (int count = 0; count < MASK_DIMENSION; count++) {
		sharpen_array_1d_double[count] = (double)(((const int *)sharpen_array_2d_int)[count]);
	}
	sharpen_mask_image = 
		vips_image_new_matrix_from_array(
			MASK_WIDTH, MASK_HEIGHT, sharpen_array_1d_double, MASK_DIMENSION
			);
	MY_ASSERT(sharpen_mask_image);

	{
		GValue value = G_VALUE_INIT;

		g_value_init(&value, G_TYPE_DOUBLE);
		g_value_set_double(&value, 24);
		vips_image_set(sharpen_mask_image, "scale", &value);
		g_value_unset(&value);
	}
	{
		GValue value = G_VALUE_INIT;

		g_value_init(&value, G_TYPE_DOUBLE);
		g_value_set_double(&value, 0);
		vips_image_set(sharpen_mask_image, "offset", &value);
		g_value_unset(&value);
	}

	ret = vips_conv(
			tmp_image, &sharpened_image,
			sharpen_mask_image,
			"precision", VIPS_PRECISION_INTEGER,
			NULL
		);
	MY_ASSERT(!ret);

	vips_image_write_to_file(normal_image, "normal.jpg", NULL);
	vips_image_write_to_file(sharpened_image, "sharpened.jpg", NULL);

	struct stat st_normal, st_sharpened;
	int size_normal, size_sharpened;

	stat("./normal.jpg", &st_normal);
	stat("./sharpened.jpg", &st_sharpened);
	size_normal = (int)st_normal.st_size;
	size_sharpened = (int)st_sharpened.st_size;

	/* On x86_64, this is "26544 28915" */
	fprintf(stdout, "%d %d\n", size_normal, size_sharpened);
	MY_ASSERT(size_sharpened > size_normal);

}
```

```
$ gcc $(rpm --eval %optflags) $(pkg-config --cflags --libs vips glib-2.0) -o resize-to-limit-test{,.c}  && ./resize-to-limit-test
```
reproduces this issue.

So C only side reproduce this. Switching to vips.

And in fact on s390x, the generated "normal.jpg" and "sharpened.jpg" are both "meaningless" images.

Reported: https://github.com/libvips/libvips/issues/4815
Workaround seems to be setting "env VIPS_NOVECTOR=1" .