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Make specialization of x64 zend_safe_address() for nmemb==1 #19203

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Merged
merged 1 commit into from
Jul 21, 2025
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Make specialization of x64 zend_safe_address() for nmemb==1 #19203

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11 changes: 10 additions & 1 deletion Zend/zend_multiply.h
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Original file line number Diff line number Diff line change
Expand Up @@ -176,7 +176,7 @@ static zend_always_inline size_t zend_safe_address(size_t nmemb, size_t size, si

static zend_always_inline size_t zend_safe_address(size_t nmemb, size_t size, size_t offset, bool *overflow)
{
size_t res = nmemb;
size_t res;
zend_ulong m_overflow = 0;

#ifdef __ILP32__ /* x32 */
Expand All @@ -186,12 +186,21 @@ static zend_always_inline size_t zend_safe_address(size_t nmemb, size_t size, si
#endif

if (ZEND_CONST_COND(offset == 0, 0)) {
res = nmemb;
__asm__ ("mul" LP_SUFF " %3\n\t"
"adc $0,%1"
: "=&a"(res), "=&d" (m_overflow)
: "%0"(res),
"rm"(size));
} else if (ZEND_CONST_COND(nmemb == 1, 0)) {
res = size;
__asm__ ("add %2, %0\n\t"
"adc $0,%1"
: "+r"(res), "+r" (m_overflow)
: "rm"(offset)
: "cc");
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Do we not need this clobber hint for the other branches?

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This also surprised me, I think we actually do need it. I don't know why it isn't there.

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Might make sense to backport that part.

} else {
res = nmemb;
__asm__ ("mul" LP_SUFF " %3\n\t"
"add %4,%0\n\t"
"adc $0,%1"
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