[Bug fortran/29549] matmul slow for complex matrices

["fxcoudert at gcc dot gnu dot org" <gcc-bugzilla@gcc.gnu.org>]

------- Comment #7 from fxcoudert at gcc dot gnu dot org  2008-02-16 18:50 -------
Thomas is right: -fcx-limited-range sets flag_complex_method to 0, but already
with flag_complex_method == 1 we have some rather good figures. Here are the
execution times of 300x300 matmul on my MacBook Pro (i386-apple-darwin8.11.1):

  - a home-made triple do loop in Fortran (Janne's comment #2) is 0.1876 sec
  - unpatched matmul is 0.5499 sec
  - matmul compiled with flag_complex_method == 1 is 0.1448 sec

The following patch is what I used to benchmark: it creates a
-fcx-fortran-rules (of course, we do know that Fortran actually rules, but
hiding it in an option name is a clever way for people to slowly start
realizing it) option that sets flag_complex_method to 1, and uses it to compile
libgfortran's matmul routines.


Index: gcc/toplev.c
===================================================================
--- gcc/toplev.c        (revision 132353)
+++ gcc/toplev.c        (working copy)
@@ -2001,6 +2001,10 @@
   if (flag_cx_limited_range)
     flag_complex_method = 0;

+  /* With -fcx-fortran-rules, we do something in-between cheap and C99.  */
+  if (flag_cx_fortran_rules)
+    flag_complex_method = 1;
+
   /* Targets must be able to place spill slots at lower addresses.  If the
      target already uses a soft frame pointer, the transition is trivial.  */
   if (!FRAME_GROWS_DOWNWARD && flag_stack_protect)
Index: gcc/common.opt
===================================================================
--- gcc/common.opt      (revision 132353)
+++ gcc/common.opt      (working copy)
@@ -390,6 +390,10 @@
 Common Report Var(flag_cx_limited_range) Optimization
 Omit range reduction step when performing complex division

+fcx-fortran-rules
+Common Report Var(flag_cx_fortran_rules) Optimization
+Complex multiplication and division follow Fortran rules
+
 fdata-sections
 Common Report Var(flag_data_sections) Optimization
 Place data items into their own section
Index: libgfortran/Makefile.am
===================================================================
--- libgfortran/Makefile.am     (revision 132353)
+++ libgfortran/Makefile.am     (working copy)
@@ -636,7 +636,7 @@
 install-pdf:

 # Turn on vectorization and loop unrolling for matmul.
-$(patsubst %.c,%.lo,$(notdir $(i_matmul_c))): AM_CFLAGS += -ftree-vectorize
-fs
+$(patsubst %.c,%.lo,$(notdir $(i_matmul_c))): AM_CFLAGS += -ftree-vectorize
-fs
 # Logical matmul doesn't vectorize.
 $(patsubst %.c,%.lo,$(notdir $(i_matmull_c))): AM_CFLAGS += -funroll-loops



-- 

fxcoudert at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |fxcoudert at gcc dot gnu dot
                   |                            |org
           Keywords|                            |patch


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29549