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[PATCH, i386]: Avoid store forwarding stalls in assign_i386_stack_local
- From: Uros Bizjak <ubizjak at gmail dot com>
- To: GCC Patches <gcc-patches at gcc dot gnu dot org>
- Date: Sat, 22 Mar 2008 20:34:09 +0100
- Subject: [PATCH, i386]: Avoid store forwarding stalls in assign_i386_stack_local
Hello!
This patch avoids store forwarding stalls in stack slots, created by
assign_i386_stack_local. We use DImode slots to load DImode values into
x87 reg usign fildll insn through the stack. When stored value crosses
16byte boundary this causes store forwarding stall.
2008-03-22 Uros Bizjak <ubizjak@gmail.com>
* config/i386/i386.c (assign_386_stack_local): Align DImode slots
to their natural alignment to avoid store forwarding stalls.
Patch is bootstrapped and regression tested on x86_64-pc-linux-gnu,
committed to SVN.
Uros.
Index: i386.c
===================================================================
--- i386.c (revision 133445)
+++ i386.c (working copy)
@@ -16315,6 +16315,7 @@ rtx
assign_386_stack_local (enum machine_mode mode, enum ix86_stack_slot n)
{
struct stack_local_entry *s;
+ int align;
gcc_assert (n < MAX_386_STACK_LOCALS);
@@ -16325,11 +16326,19 @@ assign_386_stack_local (enum machine_mod
if (s->mode == mode && s->n == n)
return copy_rtx (s->rtl);
+ /* Align DImode slots to their natural alignment
+ to avoid store forwarding stalls. */
+ if (mode == DImode
+ && (GET_MODE_BITSIZE (mode) > GET_MODE_ALIGNMENT (mode)))
+ align = GET_MODE_BITSIZE (mode);
+ else
+ align = 0;
+
s = (struct stack_local_entry *)
ggc_alloc (sizeof (struct stack_local_entry));
s->n = n;
s->mode = mode;
- s->rtl = assign_stack_local (mode, GET_MODE_SIZE (mode), 0);
+ s->rtl = assign_stack_local (mode, GET_MODE_SIZE (mode), align);
s->next = ix86_stack_locals;
ix86_stack_locals = s;