x86 definition of cas() is wrong

On x86, cas() is defined in SMP.h as (paraphrasing)

asm ("lock\ncmpxchg %3,%1"
     :"=a"(o), "=m" (*p)
     :"0"(o), "r"(n));

But *p is both read and written to, and therefore should have the '+' constraint modifier as opposed to the '=' modifier. Otherwise, the compiler is allowed to elide an earlier write to *p because it thinks that the call to cas() will overwrite it.

Trac metadata

Trac field	Value
Version	7.7
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Runtime System
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