[PATCH] i386: Don't use frame pointer without stack access

["H.J. Lu" <hjl dot tools at gmail dot com>]

When there is no stack access, there is no need to use frame pointer
even if -fno-omit-frame-pointer is used.

Tested on i686 and x86-64.  OK for trunk?

H.J.
---
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.

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/config/i386/i386.c                    | 26 ++++++++++++++------------
 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 +++++++++++
 5 files changed, 63 insertions(+), 12 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

diff --git a/gcc/config/i386/i386.c b/gcc/config/i386/i386.c
index a5984659eb2..fb16b5e77a3 100644
--- a/gcc/config/i386/i386.c
+++ b/gcc/config/i386/i386.c
@@ -14116,22 +14116,24 @@ 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 */
   unsigned int incoming_stack_boundary
     = (crtl->parm_stack_boundary > ix86_incoming_stack_boundary
        ? crtl->parm_stack_boundary : ix86_incoming_stack_boundary);
-  unsigned int stack_realign
+  bool stack_realign
     = (incoming_stack_boundary
        < (crtl->is_leaf && !ix86_current_function_calls_tls_descriptor
 	  ? crtl->max_used_stack_slot_alignment
 	  : crtl->stack_alignment_needed));
   bool recompute_frame_layout_p = false;
+  bool omit_frame_pointer = flag_omit_frame_pointer != 0;
 
   if (crtl->stack_realign_finalized)
     {
@@ -14142,13 +14144,13 @@ 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 == 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
@@ -14339,7 +14341,7 @@ 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));
@@ -15203,7 +15205,7 @@ 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;
@@ -15738,7 +15740,7 @@ 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/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" } } */
-- 
2.13.3