On Sun, Aug 8, 2010 at 7:56 AM, Uros Bizjak <[email protected]> wrote:
> Hello!
>
> After recent discussions, I would like to propose a transition to
> -fomit-frame-pointer for x86_32.
>
> The transition should be smooth as much as possible, should have
> option to revert to old behaviour and still providing path for the
> improvement. And we have learned something from cld issues, too
> (cough, cough...).
>
> I support the idea to change x86_32 defaults w.r.t. frame pointer (and
> unwind tables) to the same defaults as x86_64 has.
>
> The patch should also introduce --enable-frame-pointer configure
> option (off by default) that would revert back to old x86_32
> behaviour. So, if there are codes that depend on FP, their users (or
> distributions) should either (re-)configure the compiler with
> --enable-frame-pointer or they should use older compiler - 4.5.x will
> still be supported for many years. OTOH, it looks that users don't
> care that much whether backtraces on x86_64 are totally accurate, so
> IMO the sky won't fall down if x86_32 misses some backtraces in the
> same way. And as I have learned from the discussion, the problem is
> fixable with some effort on the user's side, thus fixing both targets
> in one shot.
>
> Of course, this change and the option to revert to the previous
> behaviour should be announced and documented in GCC release notes for
> 4.6.0.
>
> IMO, we have to bite the bullet from time to time in order to improve
> the generated code. We should not claim that gcc is
> "no-code-left-behind compiler" - from my experience, introducing new
> compiler always means that some parts of the code have to be fixed (as
> in case of the change to -fno-strict-aliasing).
>
> Uros.
>
I tested this patch on Linux/ia32 and Linux/x86-64. There are no regressions.
I don't have good wording for document:
--
For 32-bit x86 targets, it is not enabled at @option{-Os} by default.
This option also can be disabled by default on 32-bit x86 targets by
configuring GCC with the @option{--enable-frame-pointer} configure
option.
--
isn't very accurate. Any suggestions?
Thanks.
--
H.J.
---
2010-08-09 H.J. Lu <[email protected]>
* config.gcc: Handle --enable-frame-pointer.
* configure.ac: Add --enable-frame-pointer.
* configure: Regenerated.
* config/i386/i386.c (override_options): If not optimize for
size, use -fomit-frame-pointer and -fasynchronous-unwind-tables
by default for 32-bit code unless configured with
--enable-frame-pointer.
2010-08-09 H.J. Lu <[email protected]>
* config.gcc: Handle --enable-frame-pointer.
* configure.ac: Add --enable-frame-pointer.
* configure: Regenerated.
* config/i386/i386.c (override_options): If not optimize for
size, use -fomit-frame-pointer and -fasynchronous-unwind-tables
by default for 32-bit code unless configured with
--enable-frame-pointer.
diff --git a/gcc/config.gcc b/gcc/config.gcc
index 9170fc8..62dd9f6 100644
--- a/gcc/config.gcc
+++ b/gcc/config.gcc
@@ -406,6 +406,9 @@ i[34567]86-*-*)
if test "x$enable_cld" = xyes; then
tm_defines="${tm_defines} USE_IX86_CLD=1"
fi
+ if test "x$enable_frame_pointer" = xyes; then
+ tm_defines="${tm_defines} USE_IX86_FRAME_POINTER=1"
+ fi
tm_file="vxworks-dummy.h ${tm_file}"
;;
x86_64-*-*)
@@ -413,6 +416,9 @@ x86_64-*-*)
if test "x$enable_cld" = xyes; then
tm_defines="${tm_defines} USE_IX86_CLD=1"
fi
+ if test "x$enable_frame_pointer" = xyes; then
+ tm_defines="${tm_defines} USE_IX86_FRAME_POINTER=1"
+ fi
tm_file="vxworks-dummy.h ${tm_file}"
;;
esac
diff --git a/gcc/config/i386/i386.c b/gcc/config/i386/i386.c
index 1877730..c0b657b 100644
--- a/gcc/config/i386/i386.c
+++ b/gcc/config/i386/i386.c
@@ -2979,32 +2979,6 @@ override_options (bool main_args_p)
if (TARGET_MACHO && TARGET_64BIT)
flag_pic = 2;
- /* Set the default values for switches whose default depends on TARGET_64BIT
- in case they weren't overwritten by command line options. */
- if (TARGET_64BIT)
- {
- if (flag_zee == 2)
- flag_zee = 1;
- /* Mach-O doesn't support omitting the frame pointer for now. */
- if (flag_omit_frame_pointer == 2)
- flag_omit_frame_pointer = (TARGET_MACHO ? 0 : 1);
- if (flag_asynchronous_unwind_tables == 2)
- flag_asynchronous_unwind_tables = 1;
- if (flag_pcc_struct_return == 2)
- flag_pcc_struct_return = 0;
- }
- else
- {
- if (flag_zee == 2)
- flag_zee = 0;
- if (flag_omit_frame_pointer == 2)
- flag_omit_frame_pointer = 0;
- if (flag_asynchronous_unwind_tables == 2)
- flag_asynchronous_unwind_tables = 0;
- if (flag_pcc_struct_return == 2)
- flag_pcc_struct_return = DEFAULT_PCC_STRUCT_RETURN;
- }
-
/* Need to check -mtune=generic first. */
if (ix86_tune_string)
{
@@ -3292,6 +3266,49 @@ override_options (bool main_args_p)
for (i = 0; i < X86_TUNE_LAST; ++i)
ix86_tune_features[i] = !!(initial_ix86_tune_features[i] & ix86_tune_mask);
+ if ((x86_accumulate_outgoing_args & ix86_tune_mask)
+ && !(target_flags_explicit & MASK_ACCUMULATE_OUTGOING_ARGS)
+ && !optimize_size)
+ target_flags |= MASK_ACCUMULATE_OUTGOING_ARGS;
+
+ /* Set the default values for switches whose default depends on TARGET_64BIT
+ in case they weren't overwritten by command line options. */
+ if (TARGET_64BIT)
+ {
+ if (flag_zee == 2)
+ flag_zee = 1;
+ /* Mach-O doesn't support omitting the frame pointer for now. */
+ if (flag_omit_frame_pointer == 2)
+ flag_omit_frame_pointer = (TARGET_MACHO ? 0 : 1);
+ if (flag_asynchronous_unwind_tables == 2)
+ flag_asynchronous_unwind_tables = 1;
+ if (flag_pcc_struct_return == 2)
+ flag_pcc_struct_return = 0;
+ }
+ else
+ {
+ if (flag_zee == 2)
+ flag_zee = 0;
+ /* If not optimize for size, use -fomit-frame-pointer and
+ -fasynchronous-unwind-tables by default for 32-bit code
+ unless configured with --enable-frame-pointer. */
+#ifdef USE_IX86_FRAME_POINTER
+ if (flag_omit_frame_pointer == 2)
+ flag_omit_frame_pointer = 0;
+ if (flag_asynchronous_unwind_tables == 2)
+ flag_asynchronous_unwind_tables = 0;
+#else
+ if (flag_omit_frame_pointer == 2)
+ flag_omit_frame_pointer
+ = !!(target_flags & MASK_ACCUMULATE_OUTGOING_ARGS);
+ if (flag_asynchronous_unwind_tables == 2)
+ flag_asynchronous_unwind_tables
+ = !!(target_flags & MASK_ACCUMULATE_OUTGOING_ARGS);
+#endif
+ if (flag_pcc_struct_return == 2)
+ flag_pcc_struct_return = DEFAULT_PCC_STRUCT_RETURN;
+ }
+
if (optimize_size)
ix86_cost = &ix86_size_cost;
else
@@ -3574,11 +3591,6 @@ override_options (bool main_args_p)
prefix, suffix, sw);
}
- if ((x86_accumulate_outgoing_args & ix86_tune_mask)
- && !(target_flags_explicit & MASK_ACCUMULATE_OUTGOING_ARGS)
- && !optimize_size)
- target_flags |= MASK_ACCUMULATE_OUTGOING_ARGS;
-
/* ??? Unwind info is not correct around the CFG unless either a frame
pointer is present or M_A_O_A is set. Fixing this requires rewriting
unwind info generation to be aware of the CFG and propagating states
diff --git a/gcc/configure b/gcc/configure
index aa61cd6..ad548fc 100755
--- a/gcc/configure
+++ b/gcc/configure
@@ -898,6 +898,7 @@ with_system_libunwind
enable_secureplt
enable_leading_mingw64_underscores
enable_cld
+enable_frame_pointer
enable_win32_registry
enable_static
with_pic
@@ -1597,6 +1598,7 @@ Optional Features:
--enable-leading-mingw64-underscores
Enable leading underscores on 64 bit mingw targets
--enable-cld enable -mcld by default for 32bit x86
+ --enable-frame-pointer enable -fno-omit-frame-pointer by default for 32bit
x86
--disable-win32-registry
disable lookup of installation paths in the
Registry on Windows hosts
@@ -10708,6 +10710,24 @@ else
fi
+# Check whether --enable-frame-pointer was given.
+if test "${enable_frame_pointer+set}" = set; then :
+ enableval=$enable_frame_pointer;
+else
+
+case $target_os in
+linux*)
+ # Enable -fomit-frame-pointer by default for Linux.
+ enable_frame_pointer=no
+ ;;
+*)
+ enable_frame_pointer=yes
+ ;;
+esac
+
+fi
+
+
# Windows32 Registry support for specifying GCC installation paths.
# Check whether --enable-win32-registry was given.
if test "${enable_win32_registry+set}" = set; then :
@@ -17109,7 +17129,7 @@ else
lt_dlunknown=0; lt_dlno_uscore=1; lt_dlneed_uscore=2
lt_status=$lt_dlunknown
cat > conftest.$ac_ext <<_LT_EOF
-#line 17112 "configure"
+#line 17132 "configure"
#include "confdefs.h"
#if HAVE_DLFCN_H
@@ -17215,7 +17235,7 @@ else
lt_dlunknown=0; lt_dlno_uscore=1; lt_dlneed_uscore=2
lt_status=$lt_dlunknown
cat > conftest.$ac_ext <<_LT_EOF
-#line 17218 "configure"
+#line 17238 "configure"
#include "confdefs.h"
#if HAVE_DLFCN_H
diff --git a/gcc/configure.ac b/gcc/configure.ac
index 24d38aa..dd0b198 100644
--- a/gcc/configure.ac
+++ b/gcc/configure.ac
@@ -1580,6 +1580,20 @@ AC_ARG_ENABLE(cld,
[ --enable-cld enable -mcld by default for 32bit x86], [],
[enable_cld=no])
+AC_ARG_ENABLE(frame-pointer,
+[ --enable-frame-pointer enable -fno-omit-frame-pointer by default for 32bit
x86], [],
+[
+case $target_os in
+linux*)
+ # Enable -fomit-frame-pointer by default for Linux.
+ enable_frame_pointer=no
+ ;;
+*)
+ enable_frame_pointer=yes
+ ;;
+esac
+])
+
# Windows32 Registry support for specifying GCC installation paths.
AC_ARG_ENABLE(win32-registry,
[ --disable-win32-registry
