PATCH: Turn on -fomit-frame-pointer by default for 32bit Linux/x86
H.J. Lu
hjl.tools@gmail.com
Mon Jul 26 16:41:00 GMT 2010
On Wed, Jul 14, 2010 at 2:55 PM, H.J. Lu <hjl.tools@gmail.com> wrote:
> On Wed, Jul 14, 2010 at 6:46 AM, H.J. Lu <hjl.tools@gmail.com> wrote:
>> On Wed, Jul 14, 2010 at 1:09 AM, Richard Guenther
>> <richard.guenther@gmail.com> wrote:
>>> On Tue, Jul 13, 2010 at 11:44 PM, H.J. Lu <hjl.tools@gmail.com> wrote:
>>>> On Tue, Jul 13, 2010 at 2:02 PM, Andrew Pinski <pinskia@gmail.com> wrote:
>>>>> On Tue, Jul 13, 2010 at 2:01 PM, Andrew Pinski <pinskia@gmail.com> wrote:
>>>>>> On Tue, Jul 13, 2010 at 1:59 PM, H.J. Lu <hjl.tools@gmail.com> wrote:
>>>>>>> What will stop working when -fomit-frame-pointer is on?
>>>>>>
>>>>>> backtraces when debugging information is not turned on.
>>>>>
>>>>> See http://gcc.gnu.org/ml/gcc-patches/2004-08/msg01033.html and many
>>>>> more. This is not the first time this has been discussed.
>>>>
>>>> Most of 32bit x86 assembly codes in glibc have .eh_frame section.
>>>> If backtrace is absolutely needed, they can add -fasynchronous-unwind-tables
>>>> or -fno-omit-frame-pointer.
>>>
>>> We build opensuse with -fomit-frame-pointer -fasynchronous-unwind-tables.
>>> If you want to make -fomit-frame-pointer the default then you should enable
>>> unwind tables by default.
>>>
>>
>> I will try and make it target/OS dependent.
>>
>
> Here is a patch. How does it look?
>
Here are the updated patch and spread sheet for SPEC CPU 2000/2006 on
Intel Core i7 which shows that -fomit-frame-pointer -fasynchronous-unwind-tables
improves performance by up to 12% at -O2 and 8% at -O3. For -Os, it improves
performance by up to 20%, but also increases code by up to 36%.
This patch turns on -fomit-frame-pointer -fasynchronous-unwind-tables only if
-Os isn't used.
Tested on Linux/ia32 and Linux/x86-64 with -m32. OK for trunk?
Thanks.
--
H.J.
---
gcc/
2010-07-25 H.J. Lu <hongjiu.lu@intel.com>
* config/i386/i386.c (override_options): For 32bit, default
flag_omit_frame_pointer and flag_asynchronous_unwind_tables
to TARGET_SUBTARGET32_OMIT_FRAME_POINTER_DEFAULT and
TARGET_SUBTARGET32_ASYNCHRONOUS_UNWIND_TABLES_DEFAULT.
* config/i386/i386.h (TARGET_SUBTARGET32_OMIT_FRAME_POINTER_DEFAULT):
New.
(TARGET_SUBTARGET32_ASYNCHRONOUS_UNWIND_TABLES_DEFAULT): Likewise.
* config/i386/linux.h (TARGET_SUBTARGET32_OMIT_FRAME_POINTER_DEFAULT):
Likewise.
(TARGET_SUBTARGET32_ASYNCHRONOUS_UNWIND_TABLES_DEFAULT): Likewise.
* config/i386/linux64.h (TARGET_SUBTARGET32_OMIT_FRAME_POINTER_DEFAULT):
Likewise.
(TARGET_SUBTARGET32_ASYNCHRONOUS_UNWIND_TABLES_DEFAULT): Likewise.
gcc/testsuite/
2010-07-25 H.J. Lu <hongjiu.lu@intel.com>
* gcc.target/i386/frame-pointer-1.c: New.
* gcc.target/i386/frame-pointer-2.c: Likewise.
* gcc.target/i386/frame-pointer-3.c: Likewise.
* gcc.target/i386/frame-pointer-4.c: Likewise.
* gcc.target/i386/frame-pointer-5.c: Likewise.
-------------- next part --------------
gcc/
2010-07-25 H.J. Lu <hongjiu.lu@intel.com>
* config/i386/i386.c (override_options): For 32bit, default
flag_omit_frame_pointer and flag_asynchronous_unwind_tables
to TARGET_SUBTARGET32_OMIT_FRAME_POINTER_DEFAULT and
TARGET_SUBTARGET32_ASYNCHRONOUS_UNWIND_TABLES_DEFAULT.
* config/i386/i386.h (TARGET_SUBTARGET32_OMIT_FRAME_POINTER_DEFAULT):
New.
(TARGET_SUBTARGET32_ASYNCHRONOUS_UNWIND_TABLES_DEFAULT): Likewise.
* config/i386/linux.h (TARGET_SUBTARGET32_OMIT_FRAME_POINTER_DEFAULT):
Likewise.
(TARGET_SUBTARGET32_ASYNCHRONOUS_UNWIND_TABLES_DEFAULT): Likewise.
* config/i386/linux64.h (TARGET_SUBTARGET32_OMIT_FRAME_POINTER_DEFAULT):
Likewise.
(TARGET_SUBTARGET32_ASYNCHRONOUS_UNWIND_TABLES_DEFAULT): Likewise.
gcc/testsuite/
2010-07-25 H.J. Lu <hongjiu.lu@intel.com>
* gcc.target/i386/frame-pointer-1.c: New.
* gcc.target/i386/frame-pointer-2.c: Likewise.
* gcc.target/i386/frame-pointer-3.c: Likewise.
* gcc.target/i386/frame-pointer-4.c: Likewise.
* gcc.target/i386/frame-pointer-5.c: Likewise.
diff --git a/gcc/config/i386/i386.c b/gcc/config/i386/i386.c
index dbb8949..640243e 100644
--- a/gcc/config/i386/i386.c
+++ b/gcc/config/i386/i386.c
@@ -2985,10 +2985,27 @@ override_options (bool main_args_p)
{
if (flag_zee == 2)
flag_zee = 0;
+ /* Unwind info is not correct around the CFG unless either a
+ frame pointer is present or -maccumulate-outgoing-args is
+ set. When both -fasynchronous-unwind-tables and
+ -fomit-frame-pointer are turned on by default, turn off
+ both if -mno-accumulate-outgoing-args is used. When
+ optimizing for size, don't turn on -fomit-frame-pointer nor
+ -fasynchronous-unwind-tables by default. */
if (flag_omit_frame_pointer == 2)
- flag_omit_frame_pointer = 0;
+ flag_omit_frame_pointer
+ = (!optimize_size
+ && TARGET_SUBTARGET32_OMIT_FRAME_POINTER_DEFAULT
+ && (!TARGET_SUBTARGET32_ASYNCHRONOUS_UNWIND_TABLES_DEFAULT
+ || !(target_flags_explicit
+ & MASK_ACCUMULATE_OUTGOING_ARGS)));
if (flag_asynchronous_unwind_tables == 2)
- flag_asynchronous_unwind_tables = 0;
+ flag_asynchronous_unwind_tables
+ = (!optimize_size
+ && TARGET_SUBTARGET32_ASYNCHRONOUS_UNWIND_TABLES_DEFAULT
+ && (!TARGET_SUBTARGET32_OMIT_FRAME_POINTER_DEFAULT
+ || !(target_flags_explicit
+ & MASK_ACCUMULATE_OUTGOING_ARGS)));
if (flag_pcc_struct_return == 2)
flag_pcc_struct_return = DEFAULT_PCC_STRUCT_RETURN;
}
diff --git a/gcc/config/i386/i386.h b/gcc/config/i386/i386.h
index e153920..2bb6d3e 100644
--- a/gcc/config/i386/i386.h
+++ b/gcc/config/i386/i386.h
@@ -467,6 +467,8 @@ extern tree x86_mfence;
/* Extra bits to force on w/ 32-bit mode. */
#define TARGET_SUBTARGET32_DEFAULT 0
#define TARGET_SUBTARGET32_ISA_DEFAULT 0
+#define TARGET_SUBTARGET32_OMIT_FRAME_POINTER_DEFAULT 0
+#define TARGET_SUBTARGET32_ASYNCHRONOUS_UNWIND_TABLES_DEFAULT 0
/* Extra bits to force on w/ 64-bit mode. */
#define TARGET_SUBTARGET64_DEFAULT 0
diff --git a/gcc/config/i386/linux.h b/gcc/config/i386/linux.h
index 81dfd1e..61d53b5 100644
--- a/gcc/config/i386/linux.h
+++ b/gcc/config/i386/linux.h
@@ -219,3 +219,10 @@ along with GCC; see the file COPYING3. If not see
/* i386 glibc provides __stack_chk_guard in %gs:0x14. */
#define TARGET_THREAD_SSP_OFFSET 0x14
#endif
+
+/* Turn on -fomit-frame-pointer and -fasynchronous-unwind-tables by
+ default. */
+#undef TARGET_SUBTARGET32_OMIT_FRAME_POINTER_DEFAULT
+#define TARGET_SUBTARGET32_OMIT_FRAME_POINTER_DEFAULT 1
+#undef TARGET_SUBTARGET32_ASYNCHRONOUS_UNWIND_TABLES_DEFAULT
+#define TARGET_SUBTARGET32_ASYNCHRONOUS_UNWIND_TABLES_DEFAULT 1
diff --git a/gcc/config/i386/linux64.h b/gcc/config/i386/linux64.h
index 33b4dc9..5a02205 100644
--- a/gcc/config/i386/linux64.h
+++ b/gcc/config/i386/linux64.h
@@ -123,3 +123,10 @@ see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
x86_64 glibc provides it in %fs:0x28. */
#define TARGET_THREAD_SSP_OFFSET (TARGET_64BIT ? 0x28 : 0x14)
#endif
+
+/* Turn on -fomit-frame-pointer and -fasynchronous-unwind-tables by
+ default. */
+#undef TARGET_SUBTARGET32_OMIT_FRAME_POINTER_DEFAULT
+#define TARGET_SUBTARGET32_OMIT_FRAME_POINTER_DEFAULT 1
+#undef TARGET_SUBTARGET32_ASYNCHRONOUS_UNWIND_TABLES_DEFAULT
+#define TARGET_SUBTARGET32_ASYNCHRONOUS_UNWIND_TABLES_DEFAULT 1
diff --git a/gcc/testsuite/gcc.target/i386/frame-pointer-1.c b/gcc/testsuite/gcc.target/i386/frame-pointer-1.c
new file mode 100644
index 0000000..ed4bff6
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/frame-pointer-1.c
@@ -0,0 +1,13 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -mtune=i686" } */
+/* { dg-require-effective-target ilp32 } */
+
+void bar (int);
+
+void
+foo (void)
+{
+ bar (1);
+}
+
+/* { dg-final { scan-assembler-not "pushl\[\\t \]*%ebp" } } */
diff --git a/gcc/testsuite/gcc.target/i386/frame-pointer-2.c b/gcc/testsuite/gcc.target/i386/frame-pointer-2.c
new file mode 100644
index 0000000..b951ff4
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/frame-pointer-2.c
@@ -0,0 +1,13 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -mtune=i686 -mno-accumulate-outgoing-args" } */
+/* { dg-require-effective-target ilp32 } */
+
+void bar (int);
+
+void
+foo (void)
+{
+ bar (1);
+}
+
+/* { dg-final { scan-assembler "pushl\[\\t \]*%ebp" } } */
diff --git a/gcc/testsuite/gcc.target/i386/frame-pointer-3.c b/gcc/testsuite/gcc.target/i386/frame-pointer-3.c
new file mode 100644
index 0000000..7a1d4d1
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/frame-pointer-3.c
@@ -0,0 +1,13 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -mtune=i686 -mpush-args" } */
+/* { dg-require-effective-target ilp32 } */
+
+void bar (int);
+
+void
+foo (void)
+{
+ bar (1);
+}
+
+/* { dg-final { scan-assembler-not "pushl\[\\t \]*%ebp" } } */
diff --git a/gcc/testsuite/gcc.target/i386/frame-pointer-4.c b/gcc/testsuite/gcc.target/i386/frame-pointer-4.c
new file mode 100644
index 0000000..330a9ce
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/frame-pointer-4.c
@@ -0,0 +1,13 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -mtune=i686 -mpush-args -mno-accumulate-outgoing-args" } */
+/* { dg-require-effective-target ilp32 } */
+
+void bar (int);
+
+void
+foo (void)
+{
+ bar (1);
+}
+
+/* { dg-final { scan-assembler "pushl\[\\t \]*%ebp" } } */
diff --git a/gcc/testsuite/gcc.target/i386/frame-pointer-5.c b/gcc/testsuite/gcc.target/i386/frame-pointer-5.c
new file mode 100644
index 0000000..11240a2
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/frame-pointer-5.c
@@ -0,0 +1,13 @@
+/* { dg-do compile } */
+/* { dg-options "-Os -mtune=i686" } */
+/* { dg-require-effective-target ilp32 } */
+
+void bar (int);
+
+void
+foo (void)
+{
+ bar (1);
+}
+
+/* { dg-final { scan-assembler "pushl\[\\t \]*%ebp" } } */
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