[AArch64] Do not increase data alignment at -Os and with -fconserve-stack.

We unnecessarily align data to 8 byte alignments even when -Os is
specified. This brings the logic in the AArch64 backend more in line
with the ARM backend and helps gain some image size in a few
places. Caught by an internal report on the size of rodata sections
being high with aarch64 gcc.

* config/aarch64/aarch64.h (AARCH64_EXPAND_ALIGNMENT): New.
  (DATA_ALIGNMENT): Update to use AARCH64_EXPAND_ALIGNMENT.
  (LOCAL_ALIGNMENT): Update to use AARCH64_EXPAND_ALIGNMENT.

Bootstrapped and regression tested on aarch64-none-linux-gnu with no
regressions.

From-SVN: r249764

gcc/ChangeLog

+2017-06-28  Ramana Radhakrishnan  <ramana.radhakrishnan@arm.com>
+
+	* config/aarch64/aarch64.h (AARCH64_EXPAND_ALIGNMENT): New.
+	(DATA_ALIGNMENT): Update to use AARCH64_EXPAND_ALIGNMENT.
+	(LOCAL_ALIGNMENT): Update to use AARCH64_EXPAND_ALIGNMENT.
+
 2017-06-28  Sebastian Peryt  <sebastian.peryt@intel.com>
 
 	* config/i386/avx512vlintrin.h (_mm256_permutexvar_epi64)

gcc/config/aarch64/aarch64.h

@@ -98,14 +98,24 @@
     && (ALIGN) < BITS_PER_WORD)			\
    ? BITS_PER_WORD : ALIGN)
 
-#define DATA_ALIGNMENT(EXP, ALIGN)		\
-  ((((ALIGN) < BITS_PER_WORD)			\
-    && (TREE_CODE (EXP) == ARRAY_TYPE		\
-	|| TREE_CODE (EXP) == UNION_TYPE	\
-	|| TREE_CODE (EXP) == RECORD_TYPE))	\
-   ? BITS_PER_WORD : (ALIGN))
-
-#define LOCAL_ALIGNMENT(EXP, ALIGN) DATA_ALIGNMENT(EXP, ALIGN)
+/* Align definitions of arrays, unions and structures so that
+   initializations and copies can be made more efficient.  This is not
+   ABI-changing, so it only affects places where we can see the
+   definition.  Increasing the alignment tends to introduce padding,
+   so don't do this when optimizing for size/conserving stack space.  */
+#define AARCH64_EXPAND_ALIGNMENT(COND, EXP, ALIGN)			\
+  (((COND) && ((ALIGN) < BITS_PER_WORD)					\
+    && (TREE_CODE (EXP) == ARRAY_TYPE					\
+	|| TREE_CODE (EXP) == UNION_TYPE				\
+	|| TREE_CODE (EXP) == RECORD_TYPE)) ? BITS_PER_WORD : (ALIGN))
+
+/* Align global data.  */
+#define DATA_ALIGNMENT(EXP, ALIGN)			\
+  AARCH64_EXPAND_ALIGNMENT (!optimize_size, EXP, ALIGN)
+
+/* Similarly, make sure that objects on the stack are sensibly aligned.  */
+#define LOCAL_ALIGNMENT(EXP, ALIGN)				\
+  AARCH64_EXPAND_ALIGNMENT (!flag_conserve_stack, EXP, ALIGN)
 
 #define STRUCTURE_SIZE_BOUNDARY		8