diff mbox series

add alignment to enable store merging in strict-alignment targets

Message ID orft3f7rms.fsf@lxoliva.fsfla.org
State New
Headers show
Series add alignment to enable store merging in strict-alignment targets | expand

Commit Message

Alexandre Oliva Jan. 5, 2021, 7:46 a.m. UTC 
In g++.dg/opt/store-merging-2.C, the natural alignment of types T and
S is a single byte, so we shouldn't expect store merging on
strict-alignment platforms.  Indeed, without something like the
adjust-alignment pass to bump up the alignment of the automatic
variable, as in GCC 10, the optimization does not occur.

This patch adjusts the test so that the required alignment is
expressly stated, and so we don't rely on its accidentally being there
to get the desired optimization.

Regstrapped on x86_64-linux-gnu, also tested on x-arm-wrs-vxworks7r2.
Ok to install?


for  gcc/testsuite/ChangeLog

	* g++.dg/opt/store-merging-2.C: Add the required alignment.
---
 gcc/testsuite/g++.dg/opt/store-merging-2.C |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

Comments

Jeff Law Jan. 5, 2021, 5:16 p.m. UTC | #1 
On 1/5/21 12:46 AM, Alexandre Oliva wrote:
> In g++.dg/opt/store-merging-2.C, the natural alignment of types T and
> S is a single byte, so we shouldn't expect store merging on
> strict-alignment platforms.  Indeed, without something like the
> adjust-alignment pass to bump up the alignment of the automatic
> variable, as in GCC 10, the optimization does not occur.
>
> This patch adjusts the test so that the required alignment is
> expressly stated, and so we don't rely on its accidentally being there
> to get the desired optimization.
>
> Regstrapped on x86_64-linux-gnu, also tested on x-arm-wrs-vxworks7r2.
> Ok to install?
>
>
> for  gcc/testsuite/ChangeLog
>
> 	* g++.dg/opt/store-merging-2.C: Add the required alignment.
OK
jeff
diff mbox series

Patch

diff --git a/gcc/testsuite/g++.dg/opt/store-merging-2.C b/gcc/testsuite/g++.dg/opt/store-merging-2.C
index 3c17033764b75..b1ad7018a1789 100644
--- a/gcc/testsuite/g++.dg/opt/store-merging-2.C
+++ b/gcc/testsuite/g++.dg/opt/store-merging-2.C
@@ -4,7 +4,9 @@ 
 // { dg-options "-O2 -flifetime-dse=2 -fdump-tree-store-merging-details" }
 // { dg-final { scan-tree-dump "New sequence of 2 stores to replace old one of 3 stores" "store-merging" } }
 
-struct T { char a[128]; };
+/* The alignment is necessary for store-merging to take place on
+   strict-alignment targets.  */
+struct __attribute__ ((__aligned__ (4))) T { char a[128]; };
 struct S { S () : a () { a.a[12] = 0; a.a[13] = 1; a.a[14] = 0; a.a[15] = 6; } T a; };
 void foo (S &);
 void bar (void) { S s; foo (s); }