[PATCH v2] rs6000: Don't use HARD_FRAME_POINTER_REGNUM if it's not live in pro_and_epilogue (PR91518)

[luoxhu]

On 2020/4/17 08:52, Segher Boessenkool wrote:
> Hi!
> 
> On Mon, Apr 13, 2020 at 10:11:43AM +0800, luoxhu wrote:
>> frame_pointer_needed is set to true in reload pass setup_can_eliminate,
>> but regs_ever_live[31] is false, pro_and_epilogue uses it without live
>> check causing CPU2006 465.tonto segment fault of loading from invalid
>> addresses due to r31 not saved/restored.  Thus, add HARD_FRAME_POINTER_REGNUM
>> live check with frame_pointer_needed_indeed_p when generating pro_and_epilogue
>> instructions.
> 
> I see.
> 
> Can you instead make a boolean variable "frame_pointer_needed_indeed",
> that you set somewhere early in *logue processing?  So that we can be
> sure that it will not change behind our backs.


Thanks, rs6000_emit_prologue seems the proper place to set the frame_pointer_needed_indeed,
but it's strange that hard_frame_pointer_rtx will be marked USE in make_prologue_seq, also
need check here though not causing segfault? PS, this piece of code is in different file.

function.c 
static rtx_insn *
make_prologue_seq (void)
{
  if (!targetm.have_prologue ())
    return NULL;

  start_sequence ();
  rtx_insn *seq = targetm.gen_prologue ();
  emit_insn (seq);

  /* Insert an explicit USE for the frame pointer
     if the profiling is on and the frame pointer is required.  */
  if (crtl->profile && frame_pointer_needed)
    emit_use (hard_frame_pointer_rtx);
...



Any way, update the patch as below with your previous comments:



This bug is exposed by FRE refactor of r263875.  Comparing the fre
dump file shows no obvious change of the segment fault function proves
it to be a target issue.
frame_pointer_needed is set to true in reload pass setup_can_eliminate,
but regs_ever_live[31] is false, pro_and_epilogue uses it without live
check causing CPU2006 465.tonto segment fault of loading from invalid
addresses due to r31 not saved/restored.  Thus, add HARD_FRAME_POINTER_REGNUM
live check with frame_pointer_needed_indeed when generating pro_and_epilogue
instructions.

Bootstrap and regression tested pass on Power8-LE.  Backport to gcc-9
required once approved.

gcc/ChangeLog

2020-04-17  Xiong Hu Luo  <luoxhu@linux.ibm.com>

	PR target/91518
	* config/rs6000/rs6000-logue.c (frame_pointer_needed_indeed):
	New variable.
	(rs6000_emit_prologue_components):
	Check with frame_pointer_needed_indeed.
	(rs6000_emit_epilogue_components): Likewise.
	(rs6000_emit_epilogue): Likewise.
	(rs6000_emit_prologue): Set frame_pointer_needed_indeed.
---
 gcc/config/rs6000/rs6000-logue.c | 23 ++++++++++++++---------
 1 file changed, 14 insertions(+), 9 deletions(-)

diff --git a/gcc/config/rs6000/rs6000-logue.c b/gcc/config/rs6000/rs6000-logue.c
index 4cbf228eb79..2213d1fa227 100644
--- a/gcc/config/rs6000/rs6000-logue.c
+++ b/gcc/config/rs6000/rs6000-logue.c
@@ -58,6 +58,8 @@ static bool rs6000_save_toc_in_prologue_p (void);
 
 static rs6000_stack_t stack_info;
 
+/* Set if HARD_FRAM_POINTER_REGNUM is really needed.  */
+static bool frame_pointer_needed_indeed = false;
 
 /* Label number of label created for -mrelocatable, to call to so we can
    get the address of the GOT section */
@@ -2735,9 +2737,9 @@ void
 rs6000_emit_prologue_components (sbitmap components)
 {
   rs6000_stack_t *info = rs6000_stack_info ();
-  rtx ptr_reg = gen_rtx_REG (Pmode, frame_pointer_needed
-			     ? HARD_FRAME_POINTER_REGNUM
-			     : STACK_POINTER_REGNUM);
+  rtx ptr_reg = gen_rtx_REG (Pmode, frame_pointer_needed_indeed
+				      ? HARD_FRAME_POINTER_REGNUM
+				      : STACK_POINTER_REGNUM);
 
   machine_mode reg_mode = Pmode;
   int reg_size = TARGET_32BIT ? 4 : 8;
@@ -2815,9 +2817,9 @@ void
 rs6000_emit_epilogue_components (sbitmap components)
 {
   rs6000_stack_t *info = rs6000_stack_info ();
-  rtx ptr_reg = gen_rtx_REG (Pmode, frame_pointer_needed
-			     ? HARD_FRAME_POINTER_REGNUM
-			     : STACK_POINTER_REGNUM);
+  rtx ptr_reg = gen_rtx_REG (Pmode, frame_pointer_needed_indeed
+				      ? HARD_FRAME_POINTER_REGNUM
+				      : STACK_POINTER_REGNUM);
 
   machine_mode reg_mode = Pmode;
   int reg_size = TARGET_32BIT ? 4 : 8;
@@ -2996,7 +2998,10 @@ rs6000_emit_prologue (void)
                            && (lookup_attribute ("no_split_stack",
                                                  DECL_ATTRIBUTES (cfun->decl))
                                == NULL));
- 
+
+  frame_pointer_needed_indeed
+    = frame_pointer_needed && df_regs_ever_live_p (HARD_FRAME_POINTER_REGNUM);
+
   /* Offset to top of frame for frame_reg and sp respectively.  */
   HOST_WIDE_INT frame_off = 0;
   HOST_WIDE_INT sp_off = 0;
@@ -3658,7 +3663,7 @@ rs6000_emit_prologue (void)
     }
 
   /* Set frame pointer, if needed.  */
-  if (frame_pointer_needed)
+  if (frame_pointer_needed_indeed)
     {
       insn = emit_move_insn (gen_rtx_REG (Pmode, HARD_FRAME_POINTER_REGNUM),
 			     sp_reg_rtx);
@@ -4534,7 +4539,7 @@ rs6000_emit_epilogue (enum epilogue_type epilogue_type)
     }
   /* If we have a frame pointer, we can restore the old stack pointer
      from it.  */
-  else if (frame_pointer_needed)
+  else if (frame_pointer_needed_indeed)
     {
       frame_reg_rtx = sp_reg_rtx;
       if (DEFAULT_ABI == ABI_V4)
-- 
2.21.0.777.g83232e3864