Fix JIT QM_ASSIGN may be optimized out when op1 is null

[arnaud-lb]

ZVAL_COPY_CONST and its variations avoid updating Z_TYPE_P(dst_addr) when it's known to have the right value already, based on dst_info. However, when emitting code for ZEND_QM_ASSIGN, we add MAY_BE_NULL to dst_info when the SSA type and stack types disagree. I'm assuming this is done to force a type store here:

php-src/ext/opcache/jit/zend_jit_x86.dasc

Lines 959 to 963 in 88e90c6

	|| if ((dst_info & (MAY_BE_ANY|MAY_BE_UNDEF|MAY_BE_GUARD)) != MAY_BE_DOUBLE) {
	| SET_ZVAL_TYPE_INFO dst_addr, IS_DOUBLE
	|| }
	|| } else if (((dst_info & (MAY_BE_ANY|MAY_BE_UNDEF|MAY_BE_GUARD)) != (1<<Z_TYPE_P(zv))) || (dst_info & (MAY_BE_STRING|MAY_BE_ARRAY)) != 0) {
	| SET_ZVAL_TYPE_INFO dst_addr, Z_TYPE_INFO_P(zv)

Both of these conditions will be true unless Z_TYPE_P(zv) is NULL, in which case the type store is erroneously eliminated.

In this change I set res_use_info (dst_info) to 0 to force a type store. MAY_BE_ANY would also work.

This fixes #13508, but I'm not 100% confident this is correct.

ZEND_ASSIGN may have the same issue and I will look at it later.

[dstogov]

This seems already fixed in master in a better way.
Really we incorrectly narrowed res_type_info a few lines above, probably because rules for ASSIGN -> QM_ASSIGN optimization, but really QM_ASSIGN might be used in a first place.

diff --git a/ext/opcache/jit/zend_jit_trace.c b/ext/opcache/jit/zend_jit_trace.c
index f6da28375b7..c1ed5d80a66 100644
--- a/ext/opcache/jit/zend_jit_trace.c
+++ b/ext/opcache/jit/zend_jit_trace.c
@@ -5070,8 +5070,7 @@ static const void *zend_jit_trace(zend_jit_trace_rec *trace_buffer, uint32_t par
 						CHECK_OP1_TRACE_TYPE();
 						res_info = RES_INFO();
 						res_use_info = zend_jit_trace_type_to_info(
-							STACK_MEM_TYPE(stack, EX_VAR_TO_NUM(opline->result.var)))
-								& (MAY_BE_UNDEF|MAY_BE_NULL|MAY_BE_FALSE|MAY_BE_TRUE|MAY_BE_LONG|MAY_BE_DOUBLE);
+							STACK_MEM_TYPE(stack, EX_VAR_TO_NUM(opline->result.var)));
 						res_addr = RES_REG_ADDR();
 						if (Z_MODE(res_addr) != IS_REG &&
 								STACK_TYPE(stack, EX_VAR_TO_NUM(opline->result.var)) !=

Can you place take care about committing this.