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Fix fallback paths in fast_long_{add,sub}_function #17666

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Fix fallback paths in fast_long_{add,sub}_function #17666

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54324c9
Fix fallback paths in fast_long_{add,sub}_function
nielsdos Feb 1, 2025
54a5d2f
Not needed to change this
nielsdos Feb 2, 2025
2b762af
Perform int math once
nielsdos Feb 3, 2025
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12 changes: 9 additions & 3 deletions Zend/zend_operators.h
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Original file line number Diff line number Diff line change
Expand Up @@ -723,7 +723,7 @@ overflow: ZEND_ATTRIBUTE_COLD_LABEL
*/

if (UNEXPECTED((Z_LVAL_P(op1) & LONG_SIGN_MASK) == (Z_LVAL_P(op2) & LONG_SIGN_MASK)
&& (Z_LVAL_P(op1) & LONG_SIGN_MASK) != ((Z_LVAL_P(op1) + Z_LVAL_P(op2)) & LONG_SIGN_MASK))) {
&& (Z_LVAL_P(op1) & LONG_SIGN_MASK) != (((zend_ulong) Z_LVAL_P(op1) + (zend_ulong) Z_LVAL_P(op2)) & LONG_SIGN_MASK))) {
ZVAL_DOUBLE(result, (double) Z_LVAL_P(op1) + (double) Z_LVAL_P(op2));
} else {
ZVAL_LONG(result, Z_LVAL_P(op1) + Z_LVAL_P(op2));
Expand Down Expand Up @@ -804,11 +804,17 @@ overflow: ZEND_ATTRIBUTE_COLD_LABEL
ZVAL_LONG(result, llresult);
}
#else
ZVAL_LONG(result, Z_LVAL_P(op1) - Z_LVAL_P(op2));
/*
* 'result' may alias with op1 or op2, so we need to
* ensure that 'result' is not updated until after we
* have read the values of op1 and op2.
*/

if (UNEXPECTED((Z_LVAL_P(op1) & LONG_SIGN_MASK) != (Z_LVAL_P(op2) & LONG_SIGN_MASK)
&& (Z_LVAL_P(op1) & LONG_SIGN_MASK) != (Z_LVAL_P(result) & LONG_SIGN_MASK))) {
&& (Z_LVAL_P(op1) & LONG_SIGN_MASK) != (((zend_ulong) Z_LVAL_P(op1) - (zend_ulong) Z_LVAL_P(op2)) & LONG_SIGN_MASK))) {
ZVAL_DOUBLE(result, (double) Z_LVAL_P(op1) - (double) Z_LVAL_P(op2));
} else {
ZVAL_LONG(result, Z_LVAL_P(op1) - Z_LVAL_P(op2));
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I guess we're not actually testing this branch? Probably would only be used on some pretty esoteric platforms.

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I guess we're not actually testing this branch?

My bad (#17472) ;)

Probably would only be used on some pretty esoteric platforms.

Possibly not even that. Would require a compiler without ASM goto support, no builtins (SADDL etc.) and non Windows system. Plus, that compiler would need to support C11 (or at least the subset we're using).

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It's better to perform the integer math once, keeping the result in a temporary variable.
Otherwise C compiler may generate longer fast path code.

}
#endif
}
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