This is the mail archive of the
gcc-patches@gcc.gnu.org
mailing list for the GCC project.
Re: [PATCH] Ignore DECL_ALIGN of SSA_NAME underlying decls for dynamic stack realignment (PR middle-end/47735)
- From: Richard Biener <richard dot guenther at gmail dot com>
- To: Jakub Jelinek <jakub at redhat dot com>,Jakub Jelinek <jakub at redhat dot com>,Richard Henderson <rth at redhat dot com>,hjl dot tools at gmail dot com
- Cc: gcc-patches at gcc dot gnu dot org
- Date: Thu, 09 Jan 2014 21:13:02 +0100
- Subject: Re: [PATCH] Ignore DECL_ALIGN of SSA_NAME underlying decls for dynamic stack realignment (PR middle-end/47735)
- Authentication-results: sourceware.org; auth=none
- References: <20140109182202 dot GJ892 at tucnak dot redhat dot com>
Jakub Jelinek <jakub@redhat.com> wrote:
>Hi!
>
>As discussed in the PR, if a var isn't addressable and has gimple reg
>type,
>I don't see any point to honor it's DECL_ALIGN, we only refer to the
>var through SSA_NAME_VAR of SSA_NAMEs, nothing is allocated on the
>stack
>immediately and the SSA_NAMEs are turned into pseudos for which we only
>care
>about their modes and corresponding alignments if they need to be
>spilled to
>stack.
>
>Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
Ok.
Thanks,
Richard.
>2014-01-09 Jakub Jelinek <jakub@redhat.com>
>
> PR middle-end/47735
> * cfgexpand.c (expand_one_var): For SSA_NAMEs, if the underlying
> var satisfies use_register_for_decl, just take into account type
> alignment, rather than decl alignment.
>
> * gcc.target/i386/pr47735.c: New test.
>
>--- gcc/cfgexpand.c.jj 2014-01-08 19:37:33.630986939 +0100
>+++ gcc/cfgexpand.c 2014-01-09 13:38:45.073324129 +0100
>@@ -1215,8 +1215,11 @@ expand_one_var (tree var, bool toplevel,
> we conservatively assume it will be on stack even if VAR is
> eventually put into register after RA pass. For non-automatic
> variables, which won't be on stack, we collect alignment of
>- type and ignore user specified alignment. */
>- if (TREE_STATIC (var) || DECL_EXTERNAL (var))
>+ type and ignore user specified alignment. Similarly for
>+ SSA_NAMEs for which use_register_for_decl returns true. */
>+ if (TREE_STATIC (var)
>+ || DECL_EXTERNAL (var)
>+ || (TREE_CODE (origvar) == SSA_NAME && use_register_for_decl
>(var)))
> align = MINIMUM_ALIGNMENT (TREE_TYPE (var),
> TYPE_MODE (TREE_TYPE (var)),
> TYPE_ALIGN (TREE_TYPE (var)));
>--- gcc/testsuite/gcc.target/i386/pr47735.c.jj 2014-01-09
>13:30:14.410941107 +0100
>+++ gcc/testsuite/gcc.target/i386/pr47735.c 2014-01-09
>13:28:45.000000000 +0100
>@@ -0,0 +1,16 @@
>+/* PR middle-end/47735 */
>+/* { dg-do compile } */
>+/* { dg-options "-O2 -fomit-frame-pointer" } */
>+
>+unsigned
>+mulh (unsigned a, unsigned b)
>+{
>+ unsigned long long l __attribute__ ((aligned (32)))
>+ = ((unsigned long long) a * (unsigned long long) b) >> 32;
>+ return l;
>+}
>+
>+/* No need to dynamically realign the stack here. */
>+/* { dg-final { scan-assembler-not "and\[^\n\r]*%\[re\]sp" } } */
>+/* Nor use a frame pointer. */
>+/* { dg-final { scan-assembler-not "%\[re\]bp" } } */
>
> Jakub