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[Patch, fortran] PR4773 - [4.6 Regression] Unnecessary temporaries increase the runtime for channel.f90 by ~70%
- From: Paul Richard Thomas <paul dot richard dot thomas at gmail dot com>
- To: fortran at gcc dot gnu dot org, gcc-patches <gcc-patches at gcc dot gnu dot org>
- Date: Fri, 9 Jul 2010 17:04:26 +0200
- Subject: [Patch, fortran] PR4773 - [4.6 Regression] Unnecessary temporaries increase the runtime for channel.f90 by ~70%
Revision 161670 affected an optimization used for
array_lhs = array_valued_function (args...).
In order to prevent aliasing with the result, which is passed by
reference, a fairly conservative test was applied to generate a
temporary, if needed. Unfortunately, this reduced the performance of
gfortran with some code; most notably with channel.f90.
This patch tests if the 'array_lhs' has ever been host associated, on
condition that 'array_valued_function' is contained, in addition to
checking that the result is not use-associated, a pointer or a target.
If this is not the case, no temporary is generated.
Clearly some further optimization would be possible, if the
'array_lhs' were specifically not host associated to
'array_valued_function' OR ANY OF IT'S CALLEEs. This latter
condition is rather difficult to implement, which is why I have not
even tried it.
Bootstrapped and regtested on RHEL5.3/i686 - OK for trunk and.....?
2010-07-09 Paul Thomas <firstname.lastname@example.org>
* trans-expr.c (arrayfunc_assign_needs_temporary): No temporary
if the lhs has never been host associated, as well as not being
use associated, a pointer or a target.
* resolve.c (resolve_variable): Mark variables that are host
* gfortran.h: Add the host_assoc bit to the symbol_attribute
--- gcc/fortran/trans-expr.c (revision 161983)
+++ gcc/fortran/trans-expr.c (working copy)
@@ -4978,6 +4978,11 @@
+ /* A temporary is not needed if the lhs has never been host
+ associated and the procedure is contained. */
+ else if (!sym->attr.host_assoc)
+ return false;
/* A temporary is not needed if the variable is local and not
a pointer, a target or a result. */
--- gcc/fortran/gfortran.h (revision 161983)
+++ gcc/fortran/gfortran.h (working copy)
@@ -682,7 +682,8 @@
use_assoc:1, /* Symbol has been use-associated. */
use_only:1, /* Symbol has been use-associated, with ONLY. */
use_rename:1, /* Symbol has been use-associated and renamed. */
- imported:1; /* Symbol has been associated by IMPORT. */
+ imported:1, /* Symbol has been associated by IMPORT. */
+ host_assoc:1; /* Symbol has been host associated. */
unsigned in_namelist:1, in_common:1, in_equivalence:1;
unsigned function:1, subroutine:1, procedure:1;
--- gcc/fortran/resolve.c (revision 161983)
+++ gcc/fortran/resolve.c (working copy)
@@ -4772,6 +4772,15 @@
sym->entry_id = current_entry_id + 1;
+ /* If a symbol has been host_associated mark it. This is used latter,
+ to identify if aliasing is possible via host association. */
+ if (sym->attr.flavor == FL_VARIABLE
+ && gfc_current_ns->parent
+ && (gfc_current_ns->parent == sym->ns
+ || (gfc_current_ns->parent->parent
+ && gfc_current_ns->parent->parent == sym->ns)))
+ sym->attr.host_assoc = 1;
if (t == SUCCESS && resolve_procedure_expression (e) == FAILURE)
t = FAILURE;