https://llvm.org/bugs/show_bug.cgi?id=28410
Bug ID: 28410
Summary: Optimized code contains illegal movaps instruction
when using aligned attribute in typedef
Product: clang
Version: trunk
Hardware: PC
OS: Linux
Status: NEW
Severity: normal
Priority: P
Component: C++
Assignee: unassignedclangb...@nondot.org
Reporter: lukasz.c...@intel.com
CC: dgre...@apple.com, llvm-bugs@lists.llvm.org
Classification: Unclassified
clang generates MOVAPS instruction with wrongly aligned operand (resulting in
SEGFAULT) when compiling following code with optimizations enabled (-O2):
#include <stdint.h>
struct Foo
{
uint32_t data[ 13 ];
};
typedef __attribute__((aligned(16))) Foo FooDef;
int counter;
struct Bar
{
FooDef array[4];
};
__attribute__ ((noinline)) void do_sth(FooDef* foo)
{
counter += ((char*)foo)[0];
}
int main()
{
Bar* bar = new Bar();
FooDef tmp = {{0}};
for (int i = 0; i < 4; i++)
{
FooDef *foo = &bar->array[i];
*foo = tmp;
do_sth(foo);
}
return 0;
}
Explanation: aligned(16) attribute is ignored when determining sizeof(FooDef)
(so sizeof(FooDef) == 52, not 64). At the other hand optimizer assumes that the
given alignment holds for all elements of bar->array which is not true due to
sizeof(FooDef) not aligned to 16 bytes.
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