test92: refactor and fix SLJIT_MOV_U16 atomics in higher offsets for s390x

[carenas]

while this doesn't fully fix higher offset issues with atomics in s390x (with the emulation) it is worth doing and provides enough data to discuss the different approaches that could be taken to do so long term.

[zherczeg]

What is the problem (bug?) exactly?

[carenas]

What is the problem (bug?) exactly?

to begin it truncates the memory address to a 4 byte alignment but reads 8, so it bases its calculation in invalid data, past the first integer.

indeed, the reason why I couldn't come with a "fix" is also why I decided for a full rewrite (only for SLJIT_MOV_U16 case) so we could at least compare approaches and maybe come back with a better one at the end.

[zherczeg]

It uses cs not csg so it should be a 4 byte read. It is a good idea to compare multiple approaches though.

[carenas]

to help debugging here is my ad-hoc test code:

#include "sljitLir.h"
#include <stdio.h>

#if T == 16
typedef sljit_u16 test_t;
#define M SLJIT_MOV_U16
#define D 0x1337
#else
typedef sljit_u8 test_t;
#define M SLJIT_MOV_U8
#define D 0x42
#endif

typedef long (SLJIT_FUNC *func_t)(test_t *);

static func_t generate_func(void)
{
	void *code;

	struct sljit_compiler *C = sljit_create_compiler(NULL, NULL);

	sljit_emit_enter(C, 0, SLJIT_ARGS1(W, P), 2, 1, 0, 0, 0);
	sljit_emit_atomic_load(C, M, SLJIT_R0, SLJIT_S0);
	sljit_emit_op1(C, M, SLJIT_R1, 0, SLJIT_IMM, D);
	sljit_emit_atomic_store(C, M, SLJIT_R1, SLJIT_S0, SLJIT_R0);

	sljit_emit_return(C, SLJIT_MOV, SLJIT_R0, 0);

	code = sljit_generate_code(C);

	sljit_free_compiler(C);
	return (func_t)code;

}

int main(void)
{
	sljit_uw c = 0x5566aabbdeadbeef;
	func_t func = generate_func();

	for (int i = 0; i < (int)(sizeof(c)/sizeof(test_t)); i++) {
		printf("%d: %lx %hx %lx\n", i, func((test_t *)&c + i), ((test_t *)&c)[i], c);
		c = 0x5566aabbdeadbeef;
	}

	sljit_free_code((void *)func, NULL);
	return 0;
}

and the successful output (build with -DT=16) with the proposed code:

0: 5566aabb 1337 1337aabbdeadbeef
1: 5566aabb 1337 55661337deadbeef
2: deadbeef 1337 5566aabb1337beef
3: deadbeef 1337 5566aabbdead1337