On Wed, Aug 9, 2017 at 4:59 AM, Michael Matz <m...@suse.de> wrote:
> Hi,
>
> On Wed, 9 Aug 2017, H.J. Lu wrote:
>
>> > OK, but then both -f[no-]omit-frame-pointer do not have clearly defined
>> > semantics and thus shouldn't be exposed to the user?
>>
>> -f[no-]omit-frame-pointer apply to cases where a new stack frame
>> is needed. -fno-omit-frame-pointer allows you to unwind each
>> stack frame, not necessarily each function, via frame pointer.
>> -fno-omit-frame-pointer may not create a new stack frame for
>> each function, similar to LTO or function inlining. But you can still
>> unwind via frame pointer. We never guarantee that we will create
>> a new stack frame for each function. Some functions are inlined
>> completely. Some just use the caller's stack frame.
>
> Maybe something along these lines should be added to the docu of
> fno-omit-frame-pointer then. At least "Note that -fno-omit-frame-pointer
> doesn't force a frame for all functions if it isn't otherwise needed, and
> hence doesn't guarantee a frame pointer for all functions." .
>
Like this?
Note that @option{-fno-omit-frame-pointer} doesn't force a new stack
frame for all functions if it isn't otherwise needed, and hence doesn't
guarantee a new frame pointer for all functions.
Here is the updated patch with a note for -fno-omit-frame-pointer.
OK for trunk?
--
H.J.
From 4f6197699ab0904671919187c71d4a54594c1431 Mon Sep 17 00:00:00 2001
From: "H.J. Lu" <hjl.to...@gmail.com>
Date: Sun, 6 Aug 2017 06:24:36 -0700
Subject: [PATCH] i386: Don't use frame pointer without stack access
When there is no stack access, there is no need to use frame pointer
even if -fno-omit-frame-pointer is used and caller's frame pointer is
unchanged.
gcc/
PR target/81736
* config/i386/i386.c (ix86_finalize_stack_realign_flags): Renamed
to ...
(ix86_finalize_stack_frame_flags): This. Also clear
frame_pointer_needed if -fno-omit-frame-pointer is used without
stack access.
(ix86_expand_prologue): Replace ix86_finalize_stack_realign_flags
with ix86_finalize_stack_frame_flags.
(ix86_expand_epilogue): Likewise.
(ix86_expand_split_stack_prologue): Likewise.
* doc/invoke.texi: Add a note for -fno-omit-frame-pointer.
gcc/testsuite/
PR target/81736
* gcc.target/i386/pr81736-1.c: New test.
* gcc.target/i386/pr81736-2.c: Likewise.
* gcc.target/i386/pr81736-3.c: Likewise.
* gcc.target/i386/pr81736-4.c: Likewise.
* gcc.target/i386/pr81736-5.c: Likewise.
* gcc.target/i386/pr81736-6.c: Likewise.
* gcc.target/i386/pr81736-7.c: Likewise.
---
gcc/config/i386/i386.c | 23 ++++++++++++-----------
gcc/doc/invoke.texi | 4 ++++
gcc/testsuite/gcc.target/i386/pr81736-1.c | 13 +++++++++++++
gcc/testsuite/gcc.target/i386/pr81736-2.c | 14 ++++++++++++++
gcc/testsuite/gcc.target/i386/pr81736-3.c | 11 +++++++++++
gcc/testsuite/gcc.target/i386/pr81736-4.c | 11 +++++++++++
gcc/testsuite/gcc.target/i386/pr81736-5.c | 20 ++++++++++++++++++++
gcc/testsuite/gcc.target/i386/pr81736-6.c | 16 ++++++++++++++++
gcc/testsuite/gcc.target/i386/pr81736-7.c | 13 +++++++++++++
9 files changed, 114 insertions(+), 11 deletions(-)
create mode 100644 gcc/testsuite/gcc.target/i386/pr81736-1.c
create mode 100644 gcc/testsuite/gcc.target/i386/pr81736-2.c
create mode 100644 gcc/testsuite/gcc.target/i386/pr81736-3.c
create mode 100644 gcc/testsuite/gcc.target/i386/pr81736-4.c
create mode 100644 gcc/testsuite/gcc.target/i386/pr81736-5.c
create mode 100644 gcc/testsuite/gcc.target/i386/pr81736-6.c
create mode 100644 gcc/testsuite/gcc.target/i386/pr81736-7.c
diff --git a/gcc/config/i386/i386.c b/gcc/config/i386/i386.c
index 3f8519777f7..85aa4d4fbf5 100644
--- a/gcc/config/i386/i386.c
+++ b/gcc/config/i386/i386.c
@@ -14179,10 +14179,11 @@ output_probe_stack_range (rtx reg, rtx end)
return "";
}
-/* Finalize stack_realign_needed flag, which will guide prologue/epilogue
- to be generated in correct form. */
+/* Finalize stack_realign_needed and frame_pointer_needed flags, which
+ will guide prologue/epilogue to be generated in correct form. */
+
static void
-ix86_finalize_stack_realign_flags (void)
+ix86_finalize_stack_frame_flags (void)
{
/* Check if stack realign is really needed after reload, and
stores result in cfun */
@@ -14205,13 +14206,13 @@ ix86_finalize_stack_realign_flags (void)
}
/* If the only reason for frame_pointer_needed is that we conservatively
- assumed stack realignment might be needed, but in the end nothing that
- needed the stack alignment had been spilled, clear frame_pointer_needed
- and say we don't need stack realignment. */
- if (stack_realign
+ assumed stack realignment might be needed or -fno-omit-frame-pointer
+ is used, but in the end nothing that needed the stack alignment had
+ been spilled nor stack access, clear frame_pointer_needed and say we
+ don't need stack realignment. */
+ if ((stack_realign || !flag_omit_frame_pointer)
&& frame_pointer_needed
&& crtl->is_leaf
- && flag_omit_frame_pointer
&& crtl->sp_is_unchanging
&& !ix86_current_function_calls_tls_descriptor
&& !crtl->accesses_prior_frames
@@ -14402,7 +14403,7 @@ ix86_expand_prologue (void)
if (ix86_function_naked (current_function_decl))
return;
- ix86_finalize_stack_realign_flags ();
+ ix86_finalize_stack_frame_flags ();
/* DRAP should not coexist with stack_realign_fp */
gcc_assert (!(crtl->drap_reg && stack_realign_fp));
@@ -15266,7 +15267,7 @@ ix86_expand_epilogue (int style)
return;
}
- ix86_finalize_stack_realign_flags ();
+ ix86_finalize_stack_frame_flags ();
frame = m->frame;
m->fs.sp_realigned = stack_realign_fp;
@@ -15801,7 +15802,7 @@ ix86_expand_split_stack_prologue (void)
gcc_assert (flag_split_stack && reload_completed);
- ix86_finalize_stack_realign_flags ();
+ ix86_finalize_stack_frame_flags ();
frame = cfun->machine->frame;
allocate = frame.stack_pointer_offset - INCOMING_FRAME_SP_OFFSET;
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index cc0f5a00a4f..3753d8a992b 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -7366,6 +7366,10 @@ size) for 32-bit GNU/Linux x86 and 32-bit Darwin x86 targets is
@option{-fomit-frame-pointer}. You can configure GCC with the
@option{--enable-frame-pointer} configure option to change the default.
+Note that @option{-fno-omit-frame-pointer} doesn't force a new stack
+frame for all functions if it isn't otherwise needed, and hence doesn't
+guarantee a new frame pointer for all functions.
+
Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
@item -foptimize-sibling-calls
diff --git a/gcc/testsuite/gcc.target/i386/pr81736-1.c b/gcc/testsuite/gcc.target/i386/pr81736-1.c
new file mode 100644
index 00000000000..92c7bc97a0d
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr81736-1.c
@@ -0,0 +1,13 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fno-omit-frame-pointer" } */
+
+extern int i;
+
+int
+foo (void)
+{
+ return i;
+}
+
+/* No need to use a frame pointer. */
+/* { dg-final { scan-assembler-not "%\[re\]bp" } } */
diff --git a/gcc/testsuite/gcc.target/i386/pr81736-2.c b/gcc/testsuite/gcc.target/i386/pr81736-2.c
new file mode 100644
index 00000000000..a3720879937
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr81736-2.c
@@ -0,0 +1,14 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fno-omit-frame-pointer" } */
+
+int
+#ifndef __x86_64__
+__attribute__((regparm(3)))
+#endif
+foo (int i)
+{
+ return i;
+}
+
+/* No need to use a frame pointer. */
+/* { dg-final { scan-assembler-not "%\[re\]bp" } } */
diff --git a/gcc/testsuite/gcc.target/i386/pr81736-3.c b/gcc/testsuite/gcc.target/i386/pr81736-3.c
new file mode 100644
index 00000000000..c3bde7dd933
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr81736-3.c
@@ -0,0 +1,11 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fno-omit-frame-pointer" } */
+
+void
+foo (void)
+{
+ asm ("# " : : : "ebx");
+}
+
+/* Need to use a frame pointer. */
+/* { dg-final { scan-assembler "%\[re\]bp" } } */
diff --git a/gcc/testsuite/gcc.target/i386/pr81736-4.c b/gcc/testsuite/gcc.target/i386/pr81736-4.c
new file mode 100644
index 00000000000..25f50016a64
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr81736-4.c
@@ -0,0 +1,11 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fno-omit-frame-pointer" } */
+
+int
+foo (int i1, int i2, int i3, int i4, int i5, int i6, int i7)
+{
+ return i7;
+}
+
+/* Need to use a frame pointer. */
+/* { dg-final { scan-assembler "%\[re\]bp" } } */
diff --git a/gcc/testsuite/gcc.target/i386/pr81736-5.c b/gcc/testsuite/gcc.target/i386/pr81736-5.c
new file mode 100644
index 00000000000..e1602cf25ba
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr81736-5.c
@@ -0,0 +1,20 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fno-omit-frame-pointer -mavx" } */
+
+typedef int v8si __attribute__ ((vector_size (32)));
+
+void
+#ifndef __x86_64__
+__attribute__((regparm(3)))
+#endif
+foo (v8si *out_start, v8si *out_end, v8si *regions)
+{
+ v8si base = regions[3];
+ *out_start = base;
+ *out_end = base;
+}
+
+/* No need to use a frame pointer. */
+/* { dg-final { scan-assembler-not "%\[re\]bp" } } */
+/* Verify no dynamic realignment is performed. */
+/* { dg-final { scan-assembler-not "and\[^\n\r]*sp" } } */
diff --git a/gcc/testsuite/gcc.target/i386/pr81736-6.c b/gcc/testsuite/gcc.target/i386/pr81736-6.c
new file mode 100644
index 00000000000..6198574c8cc
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr81736-6.c
@@ -0,0 +1,16 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fno-omit-frame-pointer" } */
+
+struct foo
+{
+ int head;
+} a;
+
+int
+bar (void)
+{
+ return a.head != 0;
+}
+
+/* No need to use a frame pointer. */
+/* { dg-final { scan-assembler-not "%\[re\]bp" } } */
diff --git a/gcc/testsuite/gcc.target/i386/pr81736-7.c b/gcc/testsuite/gcc.target/i386/pr81736-7.c
new file mode 100644
index 00000000000..f947886e642
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr81736-7.c
@@ -0,0 +1,13 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fno-omit-frame-pointer" } */
+
+extern int foo (void);
+
+int
+bar (void)
+{
+ return foo ();
+}
+
+/* No need to use a frame pointer. */
+/* { dg-final { scan-assembler-not "%\[re\]bp" } } */
--
2.13.4
