<table border="1" cellspacing="0" cellpadding="8">
<tr>
<th>Issue</th>
<td>
<a href=https://github.com/llvm/llvm-project/issues/102172>102172</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>
Alignment discrepancies between clang and avr-gcc for `short`, `long long`, and `double`
</td>
</tr>
<tr>
<th>Labels</th>
<td>
clang
</td>
</tr>
<tr>
<th>Assignees</th>
<td>
</td>
</tr>
<tr>
<th>Reporter</th>
<td>
alexrp
</td>
</tr>
</table>
<pre>
Not sure if this is intentional on the clang side, but I thought I'd at least open an issue to find out. :slightly_smiling_face:
```console
❯ avr-gcc --version
avr-gcc (GCC) 5.4.0
❯ clang --version
clang version 18.1.8
❯ avr-gcc -fsyntax-only avr.c
❯ cat avr.c
_Static_assert(sizeof(char) == 1, "sizeof(char) == 1");
_Static_assert(_Alignof(char) == 1, "_Alignof(char) == 1");
_Static_assert(__alignof(char) == 1, "__alignof(char) == 1");
_Static_assert(sizeof(short) == 2, "sizeof(short) == 2");
_Static_assert(_Alignof(short) == 1, "_Alignof(short) == 1");
_Static_assert(__alignof(short) == 1, "__alignof(short) == 1");
_Static_assert(sizeof(unsigned short) == 2, "sizeof(unsigned short) == 2");
_Static_assert(_Alignof(unsigned short) == 1, "_Alignof(unsigned short) == 1");
_Static_assert(__alignof(unsigned short) == 1, "__alignof(unsigned short) == 1");
_Static_assert(sizeof(int) == 2, "sizeof(int) == 2");
_Static_assert(_Alignof(int) == 1, "_Alignof(int) == 1");
_Static_assert(__alignof(int) == 1, "__alignof(int) == 1");
_Static_assert(sizeof(unsigned int) == 2, "sizeof(unsigned int) == 2");
_Static_assert(_Alignof(unsigned int) == 1, "_Alignof(unsigned int) == 1");
_Static_assert(__alignof(unsigned int) == 1, "__alignof(unsigned int) == 1");
_Static_assert(sizeof(long) == 4, "sizeof(long) == 4");
_Static_assert(_Alignof(long) == 1, "_Alignof(long) == 1");
_Static_assert(__alignof(long) == 1, "__alignof(long) == 1");
_Static_assert(sizeof(unsigned long) == 4, "sizeof(unsigned long) == 4");
_Static_assert(_Alignof(unsigned long) == 1, "_Alignof(unsigned long) == 1");
_Static_assert(__alignof(unsigned long) == 1, "__alignof(unsigned long) == 1");
_Static_assert(sizeof(long long) == 8, "sizeof(long long) == 8");
_Static_assert(_Alignof(long long) == 1, "_Alignof(long long) == 1");
_Static_assert(__alignof(long long) == 1, "__alignof(long long) == 1");
_Static_assert(sizeof(unsigned long long) == 8, "sizeof(unsigned long long) == 8");
_Static_assert(_Alignof(unsigned long long) == 1, "_Alignof(unsigned long long) == 1");
_Static_assert(__alignof(unsigned long long) == 1, "__alignof(unsigned long long) == 1");
_Static_assert(sizeof(float) == 4, "sizeof(float) == 4");
_Static_assert(_Alignof(float) == 1, "_Alignof(float) == 1");
_Static_assert(__alignof(float) == 1, "__alignof(float) == 1");
_Static_assert(sizeof(double) == 4, "sizeof(double) == 4");
_Static_assert(_Alignof(double) == 1, "_Alignof(double) == 1");
_Static_assert(__alignof(double) == 1, "__alignof(double) == 1");
_Static_assert(sizeof(long double) == 4, "sizeof(long double) == 4");
_Static_assert(_Alignof(long double) == 1, "_Alignof(long double) == 1");
_Static_assert(__alignof(long double) == 1, "__alignof(long double) == 1");
❯ clang --target=avr -fsyntax-only avr.c
clang: warning: no target microcontroller specified on command line, cannot link standard libraries, please pass -mmcu=<mcu name> [-Wavr-rtlib-linking-quirks]
avr.c:6:16: error: static assertion failed due to requirement '_Alignof(short) == 1': _Alignof(short) == 1
6 | _Static_assert(_Alignof(short) == 1, "_Alignof(short) == 1");
| ^~~~~~~~~~~~~~~~~~~~
avr.c:6:32: note: expression evaluates to '2 == 1'
6 | _Static_assert(_Alignof(short) == 1, "_Alignof(short) == 1");
| ~~~~~~~~~~~~~~~~^~~~
avr.c:7:16: error: static assertion failed due to requirement '__alignof(short) == 1': __alignof(short) == 1
7 | _Static_assert(__alignof(short) == 1, "__alignof(short) == 1");
| ^~~~~~~~~~~~~~~~~~~~~
avr.c:7:33: note: expression evaluates to '2 == 1'
7 | _Static_assert(__alignof(short) == 1, "__alignof(short) == 1");
| ~~~~~~~~~~~~~~~~~^~~~
avr.c:10:16: error: static assertion failed due to requirement '_Alignof(unsigned short) == 1': _Alignof(unsigned short) == 1
10 | _Static_assert(_Alignof(unsigned short) == 1, "_Alignof(unsigned short) == 1");
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
avr.c:10:41: note: expression evaluates to '2 == 1'
10 | _Static_assert(_Alignof(unsigned short) == 1, "_Alignof(unsigned short) == 1");
| ~~~~~~~~~~~~~~~~~~~~~~~~~^~~~
avr.c:11:16: error: static assertion failed due to requirement '__alignof(unsigned short) == 1': __alignof(unsigned short) == 1
11 | _Static_assert(__alignof(unsigned short) == 1, "__alignof(unsigned short) == 1");
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
avr.c:11:42: note: expression evaluates to '2 == 1'
11 | _Static_assert(__alignof(unsigned short) == 1, "__alignof(unsigned short) == 1");
| ~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~
avr.c:31:16: error: static assertion failed due to requirement '__alignof(long long) == 1': __alignof(long long) == 1
31 | _Static_assert(__alignof(long long) == 1, "__alignof(long long) == 1");
| ^~~~~~~~~~~~~~~~~~~~~~~~~
avr.c:31:37: note: expression evaluates to '8 == 1'
31 | _Static_assert(__alignof(long long) == 1, "__alignof(long long) == 1");
| ~~~~~~~~~~~~~~~~~~~~~^~~~
avr.c:35:16: error: static assertion failed due to requirement '__alignof(unsigned long long) == 1': __alignof(unsigned long long) == 1
35 | _Static_assert(__alignof(unsigned long long) == 1, "__alignof(unsigned long long) == 1");
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
avr.c:35:46: note: expression evaluates to '8 == 1'
35 | _Static_assert(__alignof(unsigned long long) == 1, "__alignof(unsigned long long) == 1");
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~
avr.c:43:16: error: static assertion failed due to requirement '__alignof(double) == 1': __alignof(double) == 1
43 | _Static_assert(__alignof(double) == 1, "__alignof(double) == 1");
| ^~~~~~~~~~~~~~~~~~~~~~
avr.c:43:34: note: expression evaluates to '4 == 1'
43 | _Static_assert(__alignof(double) == 1, "__alignof(double) == 1");
| ~~~~~~~~~~~~~~~~~~^~~~
7 errors generated.
```
</pre>
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