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

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

[Ramana Radhakrishnan]

[-- Attachment #1: Type: text/plain, Size: 598 bytes --]

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.

Ok to commit ?


cheers
Ramana


[-- Attachment #2: data-alignment-os.txt --]
[-- Type: text/plain, Size: 1498 bytes --]

diff --git a/gcc/config/aarch64/aarch64.h b/gcc/config/aarch64/aarch64.h
index e4fb96f..95907b2 100644
--- a/gcc/config/aarch64/aarch64.h
+++ b/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
 

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

[Ramana Radhakrishnan]

Ping..

Ramana

On Tue, May 2, 2017 at 10:52 AM, Ramana Radhakrishnan
<ramana.radhakrishnan@foss.arm.com> wrote:
> 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.
>
> Ok to commit ?
>
>
> cheers
> Ramana
>

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

[James Greenhalgh]

On Tue, May 02, 2017 at 10:52:13AM +0100, Ramana Radhakrishnan wrote:
> 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.
> 
> Ok to commit ?

OK.

Thanks,
James