http://llvm.org/bugs/show_bug.cgi?id=18140
Bug ID: 18140
Summary: Clang should diagnose when parameter alignment will
not be honored due to the ABI
Product: clang
Version: unspecified
Hardware: PC
OS: Windows NT
Status: NEW
Severity: normal
Priority: P
Component: Frontend
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected]
Classification: Unclassified
$ cat t.cpp
struct S {
~S();
__declspec(align(16)) char thing[16];
};
void thing(S a, int b, S c) {}
int main() {
S s;
thing(s, 1, s);
}
$ cl -c t.cpp -nologo
t.cpp
t.cpp(5) : error C2719: 'a': formal parameter with __declspec(align('16'))
won't be aligned
t.cpp(5) : error C2719: 'c': formal parameter with __declspec(align('16'))
won't be aligned
$ clang -cc1 -triple i686-pc-win32 t.cpp -emit-llvm -o - | grep byval
define void @_Z5thing1SiS_(%struct.S* byval align 4, i32 %b, %struct.S* byval
align 4) #0 {
call void @_Z5thing1SiS_(%struct.S* byval align 4 %agg.tmp, i32 1, %struct.S*
byval align 4 %agg.tmp1)
We don't emit a diagnostic, and our use of 'byval align 4' here indicates that
we will not attempt to align the struct to more than 4 bytes. Code in
lib/CodeGen/TargetInfo.cpp implements this.
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