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List:       gcc
Subject:    atomic_load: code generation 64 bit for struct
From:       "Uecker, Martin" <Martin.Uecker () med ! uni-goettingen ! de>
Date:       2020-06-28 19:00:11
Message-ID: 1593370810.3723.7.camel () med ! uni-goettingen ! de
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Hi all,

the following code compiles into a mov instruction
on x86_64.  I wonder why. The struct has alignment 4,
so a mov might not be atomic if the struct is not
alligned to its full size.  For this reason,
I expected a call to libatomic instead  
(LLVM does this).  What am I missing?

The documentation implies that this should work
for all types.


typedef struct { float re; float im; } yy_t;

yy_t bar2(yy_t* x)
{
	yy_t r;
	__atomic_load(x, &r, __ATOMIC_SEQ_CST);
	return r;
}


https://godbolt.org/z/XcDkG_

Best,
Martin
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