On 22/01/2019 15:46, Jakub Jelinek wrote:
> On Tue, Jan 22, 2019 at 02:43:38PM +0000, Richard Earnshaw (lists) wrote:
>> PR target/88469
>> * profile-count.h (profile_count): Add dummy file with 64-bit alignment
>> on arm-based systems using gcc-6/7/8.
>>
>
>> diff --git a/gcc/profile-count.h b/gcc/profile-count.h
>> index c83fa3beb8f..ddfda2cddf4 100644
>> --- a/gcc/profile-count.h
>> +++ b/gcc/profile-count.h
>> @@ -645,6 +645,12 @@ private:
>>
>> uint64_t m_val : n_bits;
>> enum profile_quality m_quality : 3;
>> +#if defined (__arm__) && (__GNUC__ >= 6 && __GNUC__ <= 8)
>> + /* Work-around for PR88469. A bug in the gcc-6/7/8 PCS layout code
>> + incorrectly detects the alignment of a structure where the only
>> + 64-bit aligned element is a bit-field. */
>> + uint64_t m_force_alignment;
>> +#endif
>
> Adding another member is very costly.
> Can't you do something like:
> #if defined (__arm__) && (__GNUC__ >= 6 && __GNUC__ <= 8)
> #define UINT64_BITFIELD_ALIGN \
> __attribute__((__aligned__ (__alignof__ (uint64_t))))
> #else
> #define UINT64_BITFIELD_ALIGN
> #endif
> and use
> uint64_t m_val UINT64_BITFIELD_ALIGN : n_bits;
> ?
>
> Jakub
>
Close. The alignment has to come before the m_val...
PR target/88469
* profile-count.h (profile_count): Force alignment of
m_val when building on Arm-based systems with gcc-6/7/8.
OK for trunk/gcc-8?
R.
diff --git a/gcc/profile-count.h b/gcc/profile-count.h
index 06564ddf4bd..63076476400 100644
--- a/gcc/profile-count.h
+++ b/gcc/profile-count.h
@@ -649,9 +649,17 @@ public:
private:
static const uint64_t uninitialized_count = ((uint64_t) 1 << n_bits) - 1;
- uint64_t m_val : n_bits;
+#if defined (__arm__) && (__GNUC__ >= 6 && __GNUC__ <= 8)
+ /* Work-around for PR88469. A bug in the gcc-7/8 PCS layout code
+ incorrectly detects the alignment of a structure where the only
+ 64-bit aligned object is a bit-field. We force the alignment
+ of the entire field to mitigate this. */
+#define UINT64_BITFIELD_ALIGN __attribute__((aligned(8)))
+#else
+#define UINT64_BITFIELD_ALIGN
+#endif
+ uint64_t UINT64_BITFIELD_ALIGN m_val : n_bits;
enum profile_quality m_quality : 3;
-
/* Return true if both values can meaningfully appear in single function
body. We have either all counters in function local or global, otherwise
operations between them are not really defined well. */
