Hi,
Inspired by rs6000 and s390 port changes, this patch
enables loop unrolling for small size loop at O2 by default.
The default behavior is to unroll loop with unknown trip-count and
less than 4 insns by 1 time.
This improves 548.exchange2 by 3.5% on icelake and 6% on zen3 with
1.2% codesize increment. For other benchmarks the variants are minor
and overall codesize increased by 0.2%.
The kernel image size increased by 0.06%, and no impact on eembc.
Bootstrapped & regrtested on x86_64-pc-linux-gnu.
Ok for trunk?
gcc/ChangeLog:
* common/config/i386/i386-common.cc (ix86_optimization_table):
Enable loop unroll and small loop unroll at O2 by default.
* config/i386/i386-options.cc
(ix86_override_options_after_change):
Disable small loop unroll when funroll-loops enabled, reset
cunroll_grow_size when it is not explicitly enabled.
(ix86_option_override_internal): Call
ix86_override_options_after_change instead of calling
ix86_recompute_optlev_based_flags and ix86_default_align
separately.
* config/i386/i386.cc (ix86_loop_unroll_adjust): Adjust unroll
factor if -munroll-only-small-loops enabled.
* config/i386/i386.opt: Add -munroll-only-small-loops,
-param=x86-small-unroll-ninsns= for loop insn limit,
-param=x86-small-unroll-factor= for unroll factor.
* doc/invoke.texi: Document -munroll-only-small-loops,
x86-small-unroll-ninsns and x86-small-unroll-factor.
gcc/testsuite/ChangeLog:
* gcc.target/i386/pr86270.c: Add -mno-unroll-only-small-loops.
* gcc.target/i386/pr93002.c: Likewise.
---
gcc/common/config/i386/i386-common.cc | 6 ++++
gcc/config/i386/i386-options.cc | 40 ++++++++++++++++++++++---
gcc/config/i386/i386.cc | 13 ++++++++
gcc/config/i386/i386.opt | 13 ++++++++
gcc/doc/invoke.texi | 14 +++++++++
gcc/testsuite/gcc.target/i386/pr86270.c | 2 +-
gcc/testsuite/gcc.target/i386/pr93002.c | 2 +-
7 files changed, 84 insertions(+), 6 deletions(-)
diff --git a/gcc/common/config/i386/i386-common.cc
b/gcc/common/config/i386/i386-common.cc
index d6a68dc9b1d..0e580b39d14 100644
--- a/gcc/common/config/i386/i386-common.cc
+++ b/gcc/common/config/i386/i386-common.cc
@@ -1686,6 +1686,12 @@ static const struct default_options
ix86_option_optimization_table[] =
/* The STC algorithm produces the smallest code at -Os, for x86. */
{ OPT_LEVELS_2_PLUS, OPT_freorder_blocks_algorithm_, NULL,
REORDER_BLOCKS_ALGORITHM_STC },
+ { OPT_LEVELS_2_PLUS_SPEED_ONLY, OPT_funroll_loops, NULL, 1 },
+ { OPT_LEVELS_2_PLUS_SPEED_ONLY, OPT_munroll_only_small_loops, NULL, 1 },
+ /* Turns off -frename-registers and -fweb which are enabled by
+ funroll-loops. */
+ { OPT_LEVELS_ALL, OPT_frename_registers, NULL, 0 },
+ { OPT_LEVELS_ALL, OPT_fweb, NULL, 0 },
/* Turn off -fschedule-insns by default. It tends to make the
problem with not enough registers even worse. */
{ OPT_LEVELS_ALL, OPT_fschedule_insns, NULL, 0 },
diff --git a/gcc/config/i386/i386-options.cc b/gcc/config/i386/i386-options.cc
index acb2291e70f..6ea347c32e1 100644
--- a/gcc/config/i386/i386-options.cc
+++ b/gcc/config/i386/i386-options.cc
@@ -1819,8 +1819,43 @@ ix86_recompute_optlev_based_flags (struct gcc_options
*opts,
void
ix86_override_options_after_change (void)
{
+ /* Default align_* from the processor table. */
ix86_default_align (&global_options);
+
ix86_recompute_optlev_based_flags (&global_options, &global_options_set);
+
+ /* Disable unrolling small loops when there's explicit
+ -f{,no}unroll-loop. */
+ if ((OPTION_SET_P (flag_unroll_loops))
+ || (OPTION_SET_P (flag_unroll_all_loops)
+ && flag_unroll_all_loops))
+ {
+ if (!OPTION_SET_P (ix86_unroll_only_small_loops))
+ ix86_unroll_only_small_loops = 0;
+ /* Re-enable -frename-registers and -fweb if funroll-loops
+ enabled. */
+ if (!OPTION_SET_P (flag_web))
+ flag_web = flag_unroll_loops;
+ if (!OPTION_SET_P (flag_rename_registers))
+ flag_rename_registers = flag_unroll_loops;
+ if (!OPTION_SET_P (flag_cunroll_grow_size))
+ flag_cunroll_grow_size = flag_unroll_loops
+ || flag_peel_loops
+ || optimize >= 3;
+ }
+ else
+ {
+ if (!OPTION_SET_P (flag_cunroll_grow_size))
+ flag_cunroll_grow_size = flag_peel_loops || optimize >= 3;
+ /* Disables loop unrolling if -mno-unroll-only-small-loops is
+ explicitly set and -funroll-loops is not enabled. */
+ if (OPTION_SET_P (ix86_unroll_only_small_loops)
+ && !ix86_unroll_only_small_loops
+ && !(OPTION_SET_P (flag_unroll_loops)
+ || OPTION_SET_P (flag_unroll_all_loops)))
+ flag_unroll_loops = flag_unroll_all_loops = 0;
+ }
+
}
/* Clear stack slot assignments remembered from previous functions.
@@ -2332,7 +2367,7 @@ ix86_option_override_internal (bool main_args_p,
set_ix86_tune_features (opts, ix86_tune, opts->x_ix86_dump_tunes);
- ix86_recompute_optlev_based_flags (opts, opts_set);
+ ix86_override_options_after_change ();
ix86_tune_cost = processor_cost_table[ix86_tune];
/* TODO: ix86_cost should be chosen at instruction or function granuality
@@ -2363,9 +2398,6 @@ ix86_option_override_internal (bool main_args_p,
|| TARGET_64BIT_P (opts->x_ix86_isa_flags))
opts->x_ix86_regparm = REGPARM_MAX;
- /* Default align_* from the processor table. */
- ix86_default_align (opts);
-
/* Provide default for -mbranch-cost= value. */
SET_OPTION_IF_UNSET (opts, opts_set, ix86_branch_cost,
ix86_tune_cost->branch_cost);
diff --git a/gcc/config/i386/i386.cc b/gcc/config/i386/i386.cc
index 480db35f6cd..75829a5d0f4 100644
--- a/gcc/config/i386/i386.cc
+++ b/gcc/config/i386/i386.cc
@@ -23820,6 +23820,19 @@ ix86_loop_unroll_adjust (unsigned nunroll, class loop
*loop)
unsigned i;
unsigned mem_count = 0;
+ /* Unroll small size loop when unroll factor is not explicitly
+ specified. */
+ if (ix86_unroll_only_small_loops && !loop->unroll)
+ {
+ int small_unroll = 0;
+ if (loop->ninsns <= (unsigned) ix86_small_unroll_ninsns)
+ small_unroll = MIN ((unsigned) ix86_small_unroll_factor,
+ nunroll);
+ else
+ small_unroll = 1;
+ return small_unroll;
+ }
+
if (!TARGET_ADJUST_UNROLL)
return nunroll;
diff --git a/gcc/config/i386/i386.opt b/gcc/config/i386/i386.opt
index 0dbaacb57ed..a724c73c0c4 100644
--- a/gcc/config/i386/i386.opt
+++ b/gcc/config/i386/i386.opt
@@ -1214,3 +1214,16 @@ Do not use GOT to access external symbols.
-param=x86-stlf-window-ninsns=
Target Joined UInteger Var(x86_stlf_window_ninsns) Init(64) Param
Instructions number above which STFL stall penalty can be compensated.
+
+munroll-only-small-loops
+Target Var(ix86_unroll_only_small_loops) Init(0) Save
+Enable conservative small loop unrolling.
+
+-param=x86-small-unroll-ninsns=
+Target Joined UInteger Var(ix86_small_unroll_ninsns) Init(4) Param
+Insturctions number limit for loop to be unrolled under
+-munroll-only-small-loops.
+
+-param=x86-small-unroll-factor=
+Target Joined UInteger Var(ix86_small_unroll_factor) Init(2) Param
+Unroll factor for -munroll-only-small-loops.
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index cd4d3c1d72c..b6fa79eccc3 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -15779,6 +15779,14 @@ The following choices of @var{name} are available on
i386 and x86_64 targets:
@item x86-stlf-window-ninsns
Instructions number above which STFL stall penalty can be compensated.
+@item x86-small-unroll-ninsns
+If -munroll-only-small-loops is enabled, only unroll loops with instruction
+count less than this parameter. The default value is 4.
+
+@item x86-small-unroll-factor
+If -munroll-only-small-loops is enabled, reset the unroll factor with this
+value. The default value is 2 which means the loop will be unrolled once.
+
@end table
@end table
@@ -25186,6 +25194,12 @@ environments where no dynamic link is performed, like
firmwares, OS
kernels, executables linked with @option{-static} or @option{-static-pie}.
@option{-mdirect-extern-access} is not compatible with @option{-fPIC} or
@option{-fpic}.
+
+@item -munroll-only-small-loops
+@itemx -mno-unroll-only-small-loops
+@opindex munroll-only-small-loops
+Controls conservative small loop unrolling. It is default enbaled by
+O2, and unrolls loop with less than 4 insns by 1 time.
@end table
@node M32C Options
diff --git a/gcc/testsuite/gcc.target/i386/pr86270.c
b/gcc/testsuite/gcc.target/i386/pr86270.c
index 81841ef5bd7..cbc9fbb0450 100644
--- a/gcc/testsuite/gcc.target/i386/pr86270.c
+++ b/gcc/testsuite/gcc.target/i386/pr86270.c
@@ -1,5 +1,5 @@
/* { dg-do compile } */
-/* { dg-options "-O2" } */
+/* { dg-options "-O2 -mno-unroll-only-small-loops" } */
int *a;
long len;
diff --git a/gcc/testsuite/gcc.target/i386/pr93002.c
b/gcc/testsuite/gcc.target/i386/pr93002.c
index 0248fcc00a5..f75a847f75d 100644
--- a/gcc/testsuite/gcc.target/i386/pr93002.c
+++ b/gcc/testsuite/gcc.target/i386/pr93002.c
@@ -1,6 +1,6 @@
/* PR target/93002 */
/* { dg-do compile } */
-/* { dg-options "-O2" } */
+/* { dg-options "-O2 -mno-unroll-only-small-loops" } */
/* { dg-final { scan-assembler-not "cmp\[^\n\r]*-1" } } */
volatile int sink;
--
2.18.1
