John Davidson

php - When is CASE_STRICT generated?

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Message:


I am trying to find an example where PHP 8.1 generates the CASE_STRICT opcode.


I found this message from @IluTov: https://chat.stackoverflow.com/transcript/message/50366061#50366061



@Derick When no jump table can be generated.



function foo($value) {
return match ($value) {
true => 'foo',
null => 'bar',
};
}

But that example only generates IS_IDENTICAL/JMPNZ/QM_ASSIGN for each case. I tried different cases and types, but only got either the regular MATCH code with jump table or the same IS_IDENTICAL/JMPNZ/QM_ASSIGN combination.


0002 T1 = IS_IDENTICAL CV0($value) bool(true)
0003 JMPNZ T1 0008
0004 T1 = IS_IDENTICAL CV0($value) null
0005 JMPNZ T1 0010
0006 JMP 0007
0007 MATCH_ERROR CV0($value)
0008 T2 = QM_ASSIGN string("foo")
0009 JMP 0012
0010 T2 = QM_ASSIGN string("bar")
0011 JMP 0012
0012 RETURN T2

What am I missing? When is CASE_STRICT generated?



My Answer:
CASE_STRICT opcode is generated in PHP 8.1 when a switch statement has a case with a non-constant value. This can happen when using expressions or variables as case values instead of just constants.

Here is an example where PHP 8.1 generates the CASE_STRICT opcode:

php
$var = 2;

switch ($var) {
case 1:
echo "One";
break;
case $var:
echo "Two";
break;
default:
echo "Default";
}


In this example, the second case statement uses the variable `$var` as the case value, which is a non-constant value. This will trigger the generation of the CASE_STRICT opcode in PHP 8.1.

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