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Fix GH-17868: Cannot allocate memory with tracing JIT on 8.4.4 #17869

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Fix GH-17868: Cannot allocate memory with tracing JIT on 8.4.4 #17869

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Fix GH-17868: Cannot allocate memory with tracing JIT on 8.4.4
nielsdos Feb 20, 2025
b1d0019
minimize diff
nielsdos Feb 20, 2025
b478f33
remove extra check
nielsdos Feb 21, 2025
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28 changes: 21 additions & 7 deletions ext/opcache/jit/zend_jit_ir.c
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Original file line number Diff line number Diff line change
Expand Up @@ -8676,6 +8676,7 @@ static int zend_jit_push_call_frame(zend_jit_ctx *jit, const zend_op *opline, co
ir_STORE(jit_CALL(rx, This), IR_NULL);
} else {
ir_ref object_or_called_scope, call_info, call_info2, object, if_cond;
ir_ref if_cond_user = IR_UNUSED;

if (opline->op2_type == IS_CV) {
// JIT: GC_ADDREF(closure);
Expand Down Expand Up @@ -8713,15 +8714,28 @@ static int zend_jit_push_call_frame(zend_jit_ctx *jit, const zend_op *opline, co
// JIT: Z_PTR(call->This) = object_or_called_scope;
ir_STORE(jit_CALL(rx, This.value.ptr), object_or_called_scope);

// JIT: if (closure->func.op_array.run_time_cache__ptr)
if_cond = ir_IF(ir_LOAD_A(ir_ADD_OFFSET(func_ref, offsetof(zend_closure, func.op_array.run_time_cache__ptr))));
ir_IF_FALSE(if_cond);
if (!func) {
// JIT: if (closure->func.common.type & ZEND_USER_FUNCTION)
ir_ref type = ir_LOAD_U8(ir_ADD_OFFSET(func_ref, offsetof(zend_closure, func.type)));
if_cond_user = ir_IF(ir_AND_U8(type, ir_CONST_U8(ZEND_USER_FUNCTION)));
ir_IF_TRUE(if_cond_user);
}

// JIT: zend_jit_init_func_run_time_cache_helper(closure->func);
ir_CALL_1(IR_VOID, ir_CONST_FC_FUNC(zend_jit_init_func_run_time_cache_helper),
ir_ADD_OFFSET(func_ref, offsetof(zend_closure, func)));
if (!func || func->common.type == ZEND_USER_FUNCTION) {
// JIT: if (closure->func.op_array.run_time_cache__ptr)
if_cond = ir_IF(ir_LOAD_A(ir_ADD_OFFSET(func_ref, offsetof(zend_closure, func.op_array.run_time_cache__ptr))));
ir_IF_FALSE(if_cond);
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Why do we need this additional check?
We checked !RUN_TIME_CACHE(op_array) in zend_jit_init_func_run_time_cache_helper().

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@nielsdos nielsdos Feb 21, 2025 •
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I see. The check for !RUN_TIME_CACHE(op_array) already existed and I forgot that zend_jit_init_func_run_time_cache_helper() already made this check. We can remove the !RUN_TIME_CACHE check from the generated code. I'll commit that change.

On master, I see that zend_jit_init_func_run_time_cache_helper() also checks function type (not on PHP-8.4), but I think it's preferable to check it in the generated code so that we can sometimes skip generating a call to zend_jit_init_func_run_time_cache_helper() when func is known to be an internal function.

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@nielsdos nielsdos Feb 21, 2025 •
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The function type check on master was introduced in 097edc8.
The only other place that calls zend_jit_init_func_run_time_cache_helper() already knows that this is a user function.
Perhaps it's even beneficial to create 2 helper variants of zend_jit_init_func_run_time_cache_helper(): one with a function type check and one without? Then we could use the one with the check in zend_jit_push_call_frame if !func, otherwise call the helper that skips the check if it's a user function, and generate no call if it's an internal function.

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Please check, how this affects the generated JIT code size. E.g. function/tracing JIT on Symfony demo.
I suppose, this shouldn't make a big difference.

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@nielsdos nielsdos Feb 21, 2025 •
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Symfony-demo:

On function JIT:

tracing with check in IR code: 21268045
tracing with check in helper (2 helper variants): 21268045

So no difference somehow.

On tracing JIT the difference is very very small:

tracing with check in IR code: 628824
tracing with check in helper (2 helper variants): 628808

Only a difference of 16! So probably not worth creating helper variants.


ir_MERGE_WITH_EMPTY_TRUE(if_cond);
// JIT: zend_jit_init_func_run_time_cache_helper(closure->func);
ir_CALL_1(IR_VOID, ir_CONST_FC_FUNC(zend_jit_init_func_run_time_cache_helper),
ir_ADD_OFFSET(func_ref, offsetof(zend_closure, func)));

ir_MERGE_WITH_EMPTY_TRUE(if_cond);
}

if (!func) {
ir_MERGE_WITH_EMPTY_FALSE(if_cond_user);
}
}

// JIT: ZEND_CALL_NUM_ARGS(call) = num_args;
Expand Down
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